refactor: move calculate_text_length to domain, add build_chapter_payload to app-layer

- Create domain/text_utils.py with canonical calculate_text_length
  (strips chapter markers, voice markers, metadata tags)
- Remove calculate_text_length from utils.py and subtitle_utils.py
- Update all imports to use domain.text_utils directly
- Create application/chapter_selection.py with build_chapter_payload()
  (orchestrates preselection + character count + safety net)
- Replace manual chapter logic in form.py with build_chapter_payload()
- 22 new tests for text_utils and chapter_selection (1550 total)

.gitattributes

@@ -0,0 +1,15 @@
+*.py text eol=lf
+*.md text eol=lf
+*.yml text eol=lf
+*.yaml text eol=lf
+*.toml text eol=lf
+*.json text eol=lf
+*.txt text eol=lf
+*.html text eol=lf
+*.css text eol=lf
+*.js text eol=lf
+*.sh text eol=lf
+*.cfg text eol=lf
+*.ini text eol=lf
+*.svg text eol=lf
+*.j2 text eol=lf

.github/FUNDING.yml

@@ -1,6 +1,6 @@
 # These are supported funding model platforms
 
-github: [jborza, jeremiahsb, mohangk]
+github: [jborza, jeremiahsb, mohangk, k0sm0naft]
 patreon: # Replace with a single Patreon username
 open_collective: # Replace with a single Open Collective username
 ko_fi: # Replace with a single Ko-fi username

.github/workflows/test_pip.yml

@@ -1,7 +1,9 @@
-name: pip install
-run-name: pip install
+name: CI
+run-name: CI
+
 on:
   push:
+    branches: [main]
     paths:
       - '**.py'
       - 'pyproject.toml'
@@ -11,23 +13,41 @@ on:
       - 'pyproject.toml'
       - '.github/workflows/**'
   workflow_dispatch:
+
 jobs:
-  install-and-run:
+  test:
     strategy:
       matrix:
-        os: [ubuntu-latest, macos-latest, windows-latest]
+        os: [ubuntu-latest, macos-14, windows-latest]
         python-version: ['3.12']
       fail-fast: false
-    continue-on-error: true
     runs-on: ${{ matrix.os }}
     steps:
       - name: Checkout repository
-        uses: actions/checkout@v4
+        uses: actions/checkout@v7
+
       - name: Set up Python
-        uses: actions/setup-python@v5
+        uses: actions/setup-python@v6
         with:
           python-version: ${{ matrix.python-version }}
-      - name: Install from repository
-        run: python -m pip install .
-      #- name: Run abogen
-      #  run: abogen
+
+      - name: Install uv
+        uses: astral-sh/setup-uv@v8.3.1
+        with:
+          enable-cache: true
+          prune-cache: false
+          cache-dependency-glob: pyproject.toml
+
+      - name: Install system dependencies (Ubuntu)
+        if: runner.os == 'Linux'
+        run: sudo apt-get update && sudo apt-get install -y libegl1
+
+      - name: Install dependencies
+        run: uv pip install --system .[dev]
+        env:
+          UV_LINK_MODE: copy
+
+      - name: Run tests
+        env:
+          QT_QPA_PLATFORM: offscreen
+        run: pytest tests/ -v --tb=short

.github/workflows/test_publish.yml

@@ -18,7 +18,7 @@ jobs:
   build:
     runs-on: ubuntu-latest
     steps:
-    - uses: actions/checkout@v4
+    - uses: actions/checkout@v7
 
     - name: Login to Github Container Registry
       # Only if we need to push an image

.gitignore

@@ -39,3 +39,4 @@ dist/
 test_assets/
 dev_notes/
 .claude/
+.coverage

abogen/application/__init__.py

@@ -0,0 +1,8 @@
+"""Application layer for conversion flow unification.
+
+This package contains the application-level orchestration logic
+that bridges UI adapters (PyQt, WebUI) with domain functions.
+
+The main entry point is ConversionService.run() which coordinates
+planning, execution, and finalization of a conversion job.
+"""

abogen/application/chapter_selection.py

@@ -0,0 +1,62 @@
+"""Chapter selection helpers for the application layer.
+
+Builds chapter payloads with smart defaults (preselection based on
+supplement score) and character counts. Used by both WebUI and PyQt.
+"""
+
+from __future__ import annotations
+
+from typing import Any, Dict, List
+
+from abogen.domain.chapter_classification import (
+    ensure_at_least_one_chapter_enabled,
+    should_preselect_chapter,
+)
+from abogen.domain.text_utils import calculate_text_length
+
+
+def build_chapter_payload(
+    chapters: List[Any],
+    source_name: str = "",
+) -> List[Dict[str, Any]]:
+    """Build a chapter payload with preselection and character counts.
+
+    Args:
+        chapters: List of chapter-like objects with ``title`` and ``text`` attributes.
+        source_name: Fallback title for the placeholder chapter when *chapters* is empty.
+
+    Returns:
+        List of chapter dicts ready for ``PendingJob.chapters`` or ``ChapterChunkConfig``.
+    """
+    total = len(chapters)
+    payload: List[Dict[str, Any]] = []
+
+    for index, chapter in enumerate(chapters):
+        title = getattr(chapter, "title", "") or ""
+        text = getattr(chapter, "text", "") or ""
+        enabled = should_preselect_chapter(title, text, index, total)
+        payload.append(
+            {
+                "id": f"{index:04d}",
+                "index": index,
+                "title": title,
+                "text": text,
+                "characters": calculate_text_length(text),
+                "enabled": enabled,
+            }
+        )
+
+    if not payload:
+        payload.append(
+            {
+                "id": "0000",
+                "index": 0,
+                "title": source_name,
+                "text": "",
+                "characters": 0,
+                "enabled": True,
+            }
+        )
+
+    ensure_at_least_one_chapter_enabled(payload)
+    return payload

abogen/application/cleanup.py

@@ -0,0 +1,73 @@
+"""Application-layer cleanup — global resource disposal.
+
+Handles:
+- GPU/CUDA memory flush
+- TTS engine disposal (PluginManager)
+- UI-specific cleanup callbacks (registered by entry points)
+
+Called by shutdown.py at process exit and by run_conversion() per-conversion.
+"""
+
+from __future__ import annotations
+
+import gc
+from typing import Callable
+
+_UI_CLEANUPS: list[Callable[[], None]] = []
+
+
+def flush_cuda() -> None:
+    """Run GC and release CUDA cache. Safe to call multiple times."""
+    gc.collect()
+    try:
+        import torch
+        if torch.cuda.is_available():
+            torch.cuda.empty_cache()
+            torch.cuda.ipc_collect()
+    except Exception:
+        pass
+
+
+def dispose_engines() -> None:
+    """Dispose all cached TTS engines via PluginManager."""
+    try:
+        from abogen.tts_plugin.plugin_manager import get_plugin_manager
+        get_plugin_manager().dispose_all()
+    except Exception:
+        pass
+
+
+def _clear_global_voice_cache() -> None:
+    """Reset the global voice download cache state."""
+    try:
+        from abogen.voice_cache import clear_voice_cache
+        clear_voice_cache()
+    except Exception:
+        pass
+
+
+def register_ui_cleanup(fn: Callable[[], None]) -> None:
+    """Register a UI-specific cleanup callback (e.g. preview threads, temp files)."""
+    _UI_CLEANUPS.append(fn)
+
+
+def cleanup() -> None:
+    """Run all application-level cleanups. Idempotent."""
+    dispose_engines()
+    flush_cuda()
+    _clear_global_voice_cache()
+
+    for fn in _UI_CLEANUPS:
+        try:
+            fn()
+        except Exception:
+            pass
+    _UI_CLEANUPS.clear()
+
+
+__all__ = [
+    "flush_cuda",
+    "dispose_engines",
+    "register_ui_cleanup",
+    "cleanup",
+]

abogen/application/conversion_config.py

@@ -0,0 +1,95 @@
+"""Feature config objects for ConversionRequest.
+
+Each config object groups parameters for a specific feature.
+If the object is None, the feature is disabled.
+
+This keeps ConversionRequest clean: no boolean flags for feature toggles,
+no scattered parameters across unrelated fields.
+
+Domain config types (PronunciationConfig, SubtitleConfig) live in
+domain/config_types.py — domain defines the contract, app fills them.
+"""
+
+from __future__ import annotations
+
+from dataclasses import dataclass, field
+from pathlib import Path
+from typing import Any, Dict, List, Optional
+
+from abogen.domain.config_types import CoverConfig, PronunciationConfig, SubtitleConfig
+from abogen.domain.enums import OutputFormat, SaveMode
+
+
+@dataclass(frozen=True)
+class WordSubstitutionConfig:
+    """Word substitution settings.
+
+    When present on ConversionRequest, word substitution is applied
+    to the source text before chapter parsing.
+    """
+    substitutions_list: str = ""
+    case_sensitive: bool = False
+    replace_caps: bool = False
+    replace_numerals: bool = False
+    fix_punctuation: bool = False
+
+
+@dataclass(frozen=True)
+class SubtitleInputConfig:
+    """Subtitle file input settings.
+
+    When present on ConversionRequest, the source is treated as a
+    subtitle file (.srt/.ass/.vtt) or timestamp text, and the
+    subtitle-to-audio pipeline is used instead of normal text conversion.
+    """
+    is_timestamp_text: bool = False
+
+
+@dataclass(frozen=True)
+class Epub3ExportConfig:
+    """EPUB3 export settings.
+
+    When present on ConversionRequest, an EPUB3 package with
+    synchronized audio narration is generated after conversion.
+    """
+    book_id: str = ""
+
+
+@dataclass(frozen=True)
+class ChapterChunkConfig:
+    """Chapter and chunk configuration.
+
+    Groups chapter overrides, chunk data, and speaker settings
+    used by the planner to build segments.
+    """
+    chapter_overrides: List[Dict[str, Any]] = field(default_factory=list)
+    chunks: List[Dict[str, Any]] = field(default_factory=list)
+    chunk_level: str = "paragraph"
+    speaker_mode: str = "single"
+    speakers: Dict[str, Any] = field(default_factory=dict)
+
+    def __post_init__(self) -> None:
+        _VALID_CHUNK_LEVELS = ("paragraph", "sentence")
+        _VALID_SPEAKER_MODES = ("single", "multi")
+        if self.chunk_level not in _VALID_CHUNK_LEVELS:
+            raise ValueError(
+                f"chunk_level must be one of {_VALID_CHUNK_LEVELS}, got {self.chunk_level!r}"
+            )
+        if self.speaker_mode not in _VALID_SPEAKER_MODES:
+            raise ValueError(
+                f"speaker_mode must be one of {_VALID_SPEAKER_MODES}, got {self.speaker_mode!r}"
+            )
+
+
+@dataclass(frozen=True)
+class SaveConfig:
+    """Save/output settings.
+
+    Groups save mode, output folder, chapter splitting, and merge options.
+    """
+    mode: SaveMode = SaveMode.SAVE_NEXT_TO_INPUT
+    output_folder: Optional[Path] = None
+    save_chapters_separately: bool = False
+    merge_chapters_at_end: bool = True
+    separate_chapters_format: OutputFormat = OutputFormat.WAV
+    save_as_project: bool = False

abogen/application/conversion_executor.py

@@ -0,0 +1,660 @@
+"""Unified conversion executor.
+
+Takes a ConversionPlan and ports, executes the TTS conversion,
+and returns a ConversionResult. No UI imports allowed.
+
+This is Stage 6 of the conversion flow unification plan.
+"""
+
+from __future__ import annotations
+
+import logging
+import time
+from contextlib import ExitStack
+from typing import Any, Callable, Dict, List, Optional, Set, Tuple
+
+from abogen.application.conversion_models import (
+    ConversionPlan,
+)
+from abogen.application.conversion_ports import (
+    AudioSink,
+    ConversionEvents,
+    PipelineProvider,
+    SubtitleWriter,
+    VoiceResolver,
+)
+from abogen.application.conversion_result import ConversionResult
+from abogen.domain.audio_sink import open_audio_sink
+from abogen.domain.conversion_engine import (
+    SegmentStats,
+    SynthParams,
+    process_and_write_subtitles,
+    synthesize_text,
+)
+from abogen.domain.enums import OutputFormat, SubtitleMode
+from abogen.domain.normalization import TTSContext
+from abogen.domain.chapter_titles import (
+    apply_chapter_text_transforms,
+    headings_equivalent as _headings_equivalent,
+)
+from abogen.domain.output_paths import sanitize_filename_for_chapter
+from abogen.infrastructure.subtitle_writer import make_subtitle_writer
+
+
+# ─── MarkerCollector ───
+
+
+class MarkerCollector:
+    """Observes execution events and accumulates chapter/chunk markers.
+
+    Separates marker collection from synthesis logic.
+    """
+
+    def __init__(self) -> None:
+        self._chapter_markers: List[Dict[str, Any]] = []
+        self._chunk_markers: List[Dict[str, Any]] = []
+        self._current_chapter_voices: Set[Tuple[str, str]] = set()
+        self._current_chapter_index: int = 0
+        self._current_chapter_title: str = ""
+        self._current_chapter_start: float = 0.0
+
+    def on_chapter_start(
+        self, index: int, title: str, start_time: float
+    ) -> None:
+        """Record chapter start."""
+        self._current_chapter_index = index
+        self._current_chapter_title = title
+        self._current_chapter_start = start_time
+        self._current_chapter_voices.clear()
+
+    def on_segment(
+        self,
+        provider: str,
+        voice: Any,
+        voice_spec: str,
+        speaker_id: str = "narrator",
+    ) -> None:
+        """Record a voice used in this chapter (for multi-speaker tracking)."""
+        self._current_chapter_voices.add((provider, voice_spec))
+
+    def on_chunk(
+        self,
+        chunk_id: str,
+        chapter_index: int,
+        chunk_index: int,
+        start: float,
+        end: float,
+        speaker_id: str,
+        provider: str,
+        voice_spec: str,
+        level: str,
+        characters: int,
+    ) -> None:
+        """Record a chunk marker."""
+        self._chunk_markers.append({
+            "id": chunk_id,
+            "chapter_index": chapter_index,
+            "chunk_index": chunk_index,
+            "start": start,
+            "end": end,
+            "speaker_id": speaker_id,
+            "voice": {"provider": provider, "voice": voice_spec},
+            "level": level,
+            "characters": characters,
+        })
+
+    def on_chapter_end(self, end_time: float) -> None:
+        """Record chapter end and build chapter marker."""
+        voices = [
+            {"provider": p, "voice": v}
+            for p, v in sorted(self._current_chapter_voices)
+        ]
+        self._chapter_markers.append({
+            "chapter_index": self._current_chapter_index,
+            "index": self._current_chapter_index + 1,
+            "title": self._current_chapter_title,
+            "start": self._current_chapter_start,
+            "end": end_time,
+            "voices": voices,
+        })
+
+    def on_outro(
+        self,
+        start_time: float,
+        end_time: float,
+        provider: str,
+        voice_spec: str,
+    ) -> None:
+        """Record outro chapter marker."""
+        self._chapter_markers.append({
+            "chapter_index": len(self._chapter_markers),
+            "index": len(self._chapter_markers) + 1,
+            "title": "Outro",
+            "start": start_time,
+            "end": end_time,
+            "voices": [{"provider": provider, "voice": voice_spec}],
+        })
+
+    @property
+    def chapter_markers(self) -> List[Dict[str, Any]]:
+        return self._chapter_markers
+
+    @property
+    def chunk_markers(self) -> List[Dict[str, Any]]:
+        return self._chunk_markers
+
+
+def execute_conversion(
+    plan: ConversionPlan,
+    events: ConversionEvents,
+    pipeline_provider: PipelineProvider,
+    voice_resolver: VoiceResolver,
+    tts_context: TTSContext,
+    *,
+    check_cancelled: Optional[Callable[[], None]] = None,
+) -> ConversionResult:
+    """Execute a conversion plan and return the result.
+
+    Args:
+        plan: The conversion plan from build_conversion_plan()
+        events: UI-specific callbacks (log, progress, check_cancelled)
+        pipeline_provider: Provides TTS backends
+        voice_resolver: Resolves voice specs into loaded voices
+        tts_context: Normalization context for text processing
+        check_cancelled: Optional cancellation checker (overrides events.check_cancelled)
+
+    Returns:
+        ConversionResult with paths and markers
+
+    Raises:
+        ConversionCancelled: If conversion is cancelled
+    """
+    request = plan.request
+    result = ConversionResult(metadata=plan.metadata)
+    collector = MarkerCollector()
+
+    logging.info(
+        "[executor] Starting: chapters=%d intro=%s outro=%s merge=%s",
+        len(plan.chapters),
+        bool(plan.intro and plan.intro.enabled),
+        bool(plan.outro and plan.outro.enabled),
+        request.save.merge_chapters_at_end,
+    )
+
+    # Determine cancellation checker
+    if check_cancelled is None:
+        check_cancelled = lambda: events.check_cancelled()
+
+    # Stats for progress tracking
+    total_characters = sum(
+        len(ch.body_text) for ch in plan.chapters
+    )
+    if plan.intro and plan.intro.enabled:
+        total_characters += len(plan.intro.text)
+    if plan.outro and plan.outro.enabled:
+        total_characters += len(plan.outro.text)
+
+    stats = SegmentStats(
+        processed_chars=0,
+        current_time=0.0,
+        etr_start_time=time.time(),
+        total_characters=total_characters,
+    )
+
+    # Compute subtitle flag once (used in every synthesize_text call)
+    use_spacy = request.subtitle.mode not in (SubtitleMode.DISABLED, SubtitleMode.LINE)
+
+    # Output paths
+    output_layout = plan.output_layout
+    if not output_layout:
+        raise ValueError("ConversionPlan must have an output_layout")
+
+    # Determine if merged output is needed
+    merge_chapters = request.save.merge_chapters_at_end or not request.save.save_chapters_separately
+    if request.output_format == OutputFormat.M4B:
+        merge_chapters = True
+
+    # Resolve voices
+    base_voice_spec = request.voice or "M1"
+    logging.info("[executor] Resolving base voice: spec=%s", base_voice_spec)
+    base_provider, base_voice_choice, base_speed, base_steps = _resolve_voice(
+        voice_resolver, base_voice_spec, request,
+        log_callback=lambda msg: events.log(msg, level="warning"),
+    )
+    logging.info("[executor] Base voice resolved: provider=%s voice=%s speed=%.2f", base_provider, base_voice_choice, base_speed)
+
+    # Use ExitStack for resource management
+    with ExitStack() as stack:
+        # Open merged audio sink
+        audio_sink: Optional[AudioSink] = None
+        audio_path = None
+        if merge_chapters:
+            audio_path = output_layout.audio_dir / f"{_base_name(request)}{request.output_format.dot_ext}"
+            meta = plan.metadata if plan.metadata else None
+            audio_sink = stack.enter_context(
+                open_audio_sink(
+                    audio_path,
+                    request.output_format,
+                    metadata=meta,
+                    cancel_check=check_cancelled,
+                )
+            )
+            result.audio_path = audio_path
+
+        # Open subtitle writer if needed
+        subtitle_writer: Optional[SubtitleWriter] = None
+        if request.subtitle.mode != SubtitleMode.DISABLED and audio_sink:
+            subtitle_writer = make_subtitle_writer(
+                audio_path,
+                request.subtitle,
+            )
+            if subtitle_writer:
+                subtitle_writer.open()
+                stack.callback(subtitle_writer.close)
+                result.subtitle_paths.append(subtitle_writer.path)
+
+        effective_subtitle_mode = request.subtitle.mode if subtitle_writer else SubtitleMode.DISABLED
+
+        synth = SynthParams(
+            tts_context=tts_context,
+            stats=stats,
+            check_cancel=check_cancelled,
+            on_progress=lambda pct, etr: events.progress(pct, etr),
+            audio_sink=audio_sink,
+            subtitle_mode=effective_subtitle_mode,
+            max_subtitle_words=request.subtitle.max_words,
+            language=request.language,
+            use_spacy_segmentation=use_spacy,
+        )
+
+        # Chapter directory
+        chapter_dir = None
+        if request.save.save_chapters_separately and len(plan.chapters) > 1:
+            chapter_dir = output_layout.audio_dir / "chapters"
+            chapter_dir.mkdir(parents=True, exist_ok=True)
+
+        # Process intro
+        intro_emitted = False
+        if plan.intro and plan.intro.enabled and merge_chapters:
+            events.log(f"Title intro: {plan.intro.text[:80]}")
+            intro_provider, intro_voice, intro_speed, intro_steps = _resolve_voice(
+                voice_resolver, plan.intro.voice_spec, request,
+                log_callback=lambda msg: events.log(msg, level="warning"),
+            )
+            intro_backend = pipeline_provider.get(intro_provider, request.language, request.use_gpu)
+            synthesize_text(
+                text=plan.intro.text,
+                params=synth,
+                backend=intro_backend,
+                voice=intro_voice,
+                speed=intro_speed or request.speed,
+                total_steps=intro_steps,
+                chapter_sink=None,
+                preview_callback=lambda text: events.log(f"  {text[:80]}"),
+            )
+            intro_emitted = True
+            events.log("Intro synthesized.")
+
+        # Chapter loop
+        for chapter_idx, chapter in enumerate(plan.chapters, 1):
+            check_cancelled()
+
+            chapter_display = f"Chapter {chapter_idx}/{len(plan.chapters)}: {chapter.title}"
+            events.log(f"Processing {chapter_display}")
+            logging.info("[executor] Chapter %d/%d: %s", chapter_idx, len(plan.chapters), chapter.title)
+
+            # Resolve chapter voice
+            chapter_provider, chapter_voice, chapter_speed, chapter_steps = _resolve_voice(
+                voice_resolver, chapter.voice_spec, request,
+                log_callback=lambda msg: events.log(msg, level="warning"),
+            )
+            logging.info("[executor] Chapter %d voice: provider=%s voice=%s speed=%.2f", chapter_idx, chapter_provider, chapter_voice, chapter_speed)
+            chapter_backend = pipeline_provider.get(chapter_provider, request.language, request.use_gpu)
+
+            # Record chapter start for markers
+            collector.on_chapter_start(chapter_idx - 1, chapter.title, stats.current_time)
+
+            # Per-chapter sink
+            chapter_sink: Optional[AudioSink] = None
+            chapter_path = None
+            if chapter_dir:
+                chapter_filename = sanitize_filename_for_chapter(chapter.title, chapter_idx)
+                chapter_path = chapter_dir / f"{chapter_filename}.{request.save.separate_chapters_format}"
+                chapter_sink = stack.enter_context(
+                    open_audio_sink(
+                        chapter_path,
+                        request.save.separate_chapters_format,
+                        cancel_check=check_cancelled,
+                    )
+                )
+                result.chapter_paths.append(chapter_path)
+
+            # Per-chapter subtitle writer
+            chapter_subtitle_writer: Optional[SubtitleWriter] = None
+            if chapter_dir and request.subtitle.mode != SubtitleMode.DISABLED and chapter_sink:
+                from abogen.infrastructure.subtitle_writer import resolve_subtitle_format
+
+                chapter_filename = sanitize_filename_for_chapter(chapter.title, chapter_idx)
+                subtitle_ext, _ = resolve_subtitle_format(
+                    request.subtitle
+                )
+                chapter_subtitle_path = chapter_dir / f"{chapter_filename}.{subtitle_ext}"
+                chapter_subtitle_writer = make_subtitle_writer(
+                    chapter_subtitle_path,
+                    request.subtitle,
+                )
+                if chapter_subtitle_writer:
+                    chapter_subtitle_writer.open()
+                    result.subtitle_paths.append(chapter_subtitle_writer.path)
+
+            # Intro delay before first chapter
+            if not intro_emitted and plan.intro and plan.intro.enabled:
+                # Intro will be emitted with first chapter
+                intro_provider, intro_voice, intro_speed, intro_steps = _resolve_voice(
+                    voice_resolver, plan.intro.voice_spec, request,
+                    log_callback=lambda msg: events.log(msg, level="warning"),
+                )
+                intro_backend = pipeline_provider.get(intro_provider, request.language, request.use_gpu)
+                synthesize_text(
+                    text=plan.intro.text,
+                    params=synth,
+                    backend=intro_backend,
+                    voice=intro_voice,
+                    speed=intro_speed or request.speed,
+                    total_steps=intro_steps,
+                    chapter_sink=chapter_sink,
+                    preview_callback=lambda text: events.log(f"  Intro: {text[:80]}"),
+                )
+                intro_emitted = True
+                if request.chapter_intro_delay > 0:
+                    _append_silence(
+                        request.chapter_intro_delay,
+                        chapter_sink=chapter_sink,
+                        audio_sink=audio_sink,
+                        stats=stats,
+                    )
+
+            # Process heading
+            heading_text = ""
+            if chapter.title:
+                heading_text = _format_heading(chapter.title, chapter_idx, request)
+                if heading_text:
+                    synthesize_text(
+                        text=heading_text,
+                        params=synth,
+                        backend=chapter_backend,
+                        voice=chapter_voice,
+                        speed=chapter_speed or request.speed,
+                        chapter_sink=chapter_sink,
+                        preview_callback=lambda text: events.log(f"  Title: {text[:80]}"),
+                    )
+                    if request.chapter_intro_delay > 0:
+                        _append_silence(
+                            request.chapter_intro_delay,
+                            chapter_sink=chapter_sink,
+                            audio_sink=audio_sink,
+                            stats=stats,
+                        )
+
+            # Heading dedup: check if first line of body matches heading
+            pending_heading_strip = False
+            if heading_text and chapter.body_text:
+                first_line = next(
+                    (line.strip() for line in chapter.body_text.splitlines() if line.strip()),
+                    "",
+                )
+                if first_line and _headings_equivalent(first_line, heading_text):
+                    pending_heading_strip = True
+
+            # Process body segments
+            for seg_idx, segment in enumerate(chapter.segments):
+                check_cancelled()
+
+                # Apply heading dedup to first segment (consume-once)
+                seg_text = segment.text
+                if pending_heading_strip and seg_text.strip():
+                    seg_text, heading_removed, _ = apply_chapter_text_transforms(
+                        seg_text,
+                        heading_text=heading_text,
+                        raw_title=chapter.title,
+                        strip_heading=True,
+                        normalize_caps=False,
+                    )
+                    if heading_removed:
+                        pending_heading_strip = False
+                    if not seg_text.strip():
+                        continue
+
+                # Resolve segment voice (may differ from chapter voice)
+                if segment.voice_spec != chapter.voice_spec:
+                    seg_provider, seg_voice, seg_speed, seg_steps = _resolve_voice(
+                        voice_resolver, segment.voice_spec, request,
+                        log_callback=lambda msg: events.log(msg, level="warning"),
+                    )
+                    seg_backend = pipeline_provider.get(seg_provider, request.language, request.use_gpu)
+                else:
+                    seg_provider = chapter_provider
+                    seg_voice = chapter_voice
+                    seg_speed = chapter_speed
+                    seg_steps = chapter_steps
+                    seg_backend = chapter_backend
+
+                # Track voice for chapter marker
+                collector.on_segment(seg_provider, seg_voice, segment.voice_spec)
+
+                # spaCy pre-TTS segmentation
+                from abogen.domain.conversion_pipeline import spacy_pre_tts_segmentation
+
+                is_subtitle_input = bool(
+                    request.subtitle_input
+                )
+                spacy_segments, active_split = spacy_pre_tts_segmentation(
+                    seg_text,
+                    request.language,
+                    request.subtitle.mode,
+                    is_subtitle_input=is_subtitle_input,
+                    use_spacy_segmentation=use_spacy,
+                    log_callback=lambda msg: events.log(msg),
+                )
+
+                seg_start_time = stats.current_time
+                accumulated_tokens: List[Dict[str, Any]] = []
+                for spacy_seg in spacy_segments:
+                    if not spacy_seg.strip():
+                        continue
+                    _, seg_tokens = synthesize_text(
+                        text=spacy_seg,
+                        params=synth,
+                        backend=seg_backend,
+                        voice=seg_voice,
+                        speed=seg_speed or request.speed,
+                        total_steps=seg_steps,
+                        chapter_sink=chapter_sink,
+                        preview_callback=lambda text: events.log(f"  {text[:80]}"),
+                        split_pattern_override=active_split,
+                    )
+                    accumulated_tokens.extend(seg_tokens)
+
+                # Process subtitles
+                if audio_sink and accumulated_tokens:
+                    if subtitle_writer:
+                        process_and_write_subtitles(
+                            accumulated_tokens,
+                            subtitle_writer,
+                            subtitle=request.subtitle,
+                            language=request.language,
+                            use_spacy_segmentation=use_spacy,
+                            fallback_end_time=stats.current_time,
+                        )
+                    if chapter_subtitle_writer:
+                        process_and_write_subtitles(
+                            accumulated_tokens,
+                            chapter_subtitle_writer,
+                            subtitle=request.subtitle,
+                            language=request.language,
+                            use_spacy_segmentation=use_spacy,
+                            fallback_end_time=stats.current_time,
+                        )
+
+                # Record chunk marker
+                if segment.source in ("chunk", "voice_marker"):
+                    collector.on_chunk(
+                        chunk_id=segment.chunk_id or "",
+                        chapter_index=chapter_idx - 1,
+                        chunk_index=segment.chunk_index or seg_idx,
+                        start=seg_start_time,
+                        end=stats.current_time,
+                        speaker_id=segment.speaker_id or "narrator",
+                        provider=seg_provider,
+                        voice_spec=segment.voice_spec,
+                        level=segment.level or (request.chapter_chunk.chunk_level if request.chapter_chunk else "paragraph"),
+                        characters=len(segment.text),
+                    )
+
+            # Silence between chapters
+            if chapter_idx < len(plan.chapters) and request.silence_between_chapters > 0:
+                _append_silence(
+                    request.silence_between_chapters,
+                    chapter_sink=chapter_sink,
+                    audio_sink=audio_sink,
+                    stats=stats,
+                )
+
+            # Close chapter sink
+            if chapter_sink:
+                chapter_sink.close()
+
+            # Close chapter subtitle writer
+            if chapter_subtitle_writer:
+                chapter_subtitle_writer.close()
+
+            # Record chapter end for markers
+            collector.on_chapter_end(stats.current_time)
+            logging.info("[executor] Chapter %d/%d done: time=%.1fs", chapter_idx, len(plan.chapters), stats.current_time)
+
+        logging.info("[executor] All chapters done: total=%.1fs", stats.current_time)
+
+        # Process outro
+        if plan.outro and plan.outro.enabled and merge_chapters:
+            events.log(f"Closing outro: {plan.outro.text[:80]}")
+            outro_provider, outro_voice, outro_speed, outro_steps = _resolve_voice(
+                voice_resolver, plan.outro.voice_spec, request,
+                log_callback=lambda msg: events.log(msg, level="warning"),
+            )
+            outro_backend = pipeline_provider.get(outro_provider, request.language, request.use_gpu)
+
+            # Silence before outro
+            if request.silence_between_chapters > 0:
+                _append_silence(
+                    request.silence_between_chapters,
+                    chapter_sink=None,
+                    audio_sink=audio_sink,
+                    stats=stats,
+                )
+
+            outro_start = stats.current_time
+            synthesize_text(
+                text=plan.outro.text,
+                params=synth,
+                backend=outro_backend,
+                voice=outro_voice,
+                speed=outro_speed or request.speed,
+                total_steps=outro_steps,
+                chapter_sink=None,
+                preview_callback=lambda text: events.log(f"  {text[:80]}"),
+            )
+            # Record outro marker
+            collector.on_outro(outro_start, stats.current_time, outro_provider, plan.outro.voice_spec)
+            events.log("Outro synthesized.")
+
+    # Set result metadata
+    result.chapter_markers = collector.chapter_markers
+    result.chunk_markers = collector.chunk_markers
+    result.total_chapters = len(plan.chapters)
+    result.total_segments = sum(len(ch.segments) for ch in plan.chapters)
+    result.total_characters = total_characters
+
+    if output_layout.project_root:
+        result.project_root = output_layout.project_root
+
+    return result
+
+
+# ─── Helpers ────────────────────────────────────────────────────────
+
+
+def _resolve_voice(
+    resolver: VoiceResolver,
+    voice_spec: str,
+    request: Any,
+    *,
+    log_callback: Optional[Callable[[str], None]] = None,
+) -> Tuple[str, Any, Optional[float], Optional[int]]:
+    """Resolve a voice spec and return (provider, voice, speed, steps)."""
+    try:
+        resolved = resolver.resolve(voice_spec)
+        return (
+            resolved.provider,
+            resolved.voice,
+            resolved.speed,
+            resolved.supertonic_steps,
+        )
+    except Exception as exc:
+        # Fallback to base voice
+        base_spec = request.voice or "M1"
+        if log_callback:
+            log_callback(
+                f"Voice '{voice_spec}' failed to resolve: {exc}. "
+                f"Falling back to '{base_spec}'."
+            )
+        try:
+            resolved = resolver.resolve(base_spec)
+        except Exception as fallback_exc:
+            raise RuntimeError(
+                f"Both voice '{voice_spec}' and fallback '{base_spec}' failed to resolve. "
+                f"Primary error: {exc}; Fallback error: {fallback_exc}"
+            ) from fallback_exc
+        return (
+            resolved.provider,
+            resolved.voice,
+            resolved.speed,
+            resolved.supertonic_steps,
+        )
+
+
+def _base_name(request: Any) -> str:
+    """Get base name for output file."""
+    from abogen.domain.output_paths import sanitize_output_stem
+
+    if request.original_filename:
+        return sanitize_output_stem(request.original_filename)
+    return "output"
+
+
+def _format_heading(title: str, index: int, request: Any) -> str:
+    """Format chapter heading for TTS."""
+    from abogen.domain.chapter_titles import format_spoken_chapter_title
+
+    if request.auto_prefix_chapter_titles:
+        return format_spoken_chapter_title(title, index, apply_prefix=True)
+    return title
+
+
+def _append_silence(
+    duration: float,
+    *,
+    chapter_sink: Optional[AudioSink],
+    audio_sink: Optional[AudioSink],
+    stats: SegmentStats,
+) -> None:
+    """Append silence to sinks."""
+    from abogen.domain.audio_buffer import create_silence
+
+    silence = create_silence(duration)
+    if silence.size == 0:
+        return
+    if chapter_sink:
+        chapter_sink.write(silence)
+    if audio_sink:
+        audio_sink.write(silence)
+        stats.current_time += duration

abogen/application/conversion_models.py

@@ -0,0 +1,97 @@
+"""Core models for conversion planning.
+
+These dataclasses represent the structured plan for a conversion job.
+They are UI-agnostic and describe WHAT to convert, not HOW to do it.
+
+The planning flow:
+    ConversionRequest -> ConversionPlan -> ConversionResult
+
+    ConversionPlan contains:
+    - ChapterPlan[]: chapters with their segments
+    - SegmentPlan[]: individual text segments with voice specs
+    - OutputLayout: where to write outputs
+    - IntroOutroSpec: optional intro/outro
+"""
+
+from __future__ import annotations
+
+from dataclasses import dataclass
+from pathlib import Path
+from typing import TYPE_CHECKING, Any, Dict, List, Optional
+
+if TYPE_CHECKING:
+    from abogen.application.conversion_request import ConversionRequest
+    from abogen.text_extractor import ExtractionResult
+
+
+@dataclass
+class SegmentPlan:
+    """A single text segment with its voice specification.
+
+    This is the unified model for:
+    - Regular chapter body text
+    - PyQt voice markers (<<VOICE:F1>>)
+    - WebUI chunks with per-chunk voice/speaker
+    - Intro/outro text
+    - Chapter headings
+    """
+
+    text: str
+    voice_spec: str
+    kind: str = "body"  # intro, heading, body, outro
+    speaker_id: str = "narrator"
+    chunk_id: Optional[str] = None
+    chunk_index: Optional[int] = None
+    level: Optional[str] = None  # chunk level (paragraph, sentence, etc.)
+    source: str = "chapter"  # chapter, voice_marker, chunk
+
+
+@dataclass
+class ChapterPlan:
+    """A chapter with its metadata and segments."""
+
+    index: int
+    title: str
+    original_title: str
+    body_text: str
+    segments: List[SegmentPlan]
+    voice_spec: str  # default voice for this chapter
+
+
+@dataclass
+class OutputLayout:
+    """Resolved output paths for a conversion job."""
+
+    parent_dir: Path
+    merged_path: Optional[Path] = None
+    chapter_dir: Optional[Path] = None
+    project_root: Optional[Path] = None
+    audio_dir: Optional[Path] = None
+    subtitle_dir: Optional[Path] = None
+    metadata_dir: Optional[Path] = None
+
+
+@dataclass
+class IntroOutroSpec:
+    """Intro/outro specification with resolved text and voice."""
+
+    enabled: bool = False
+    text: str = ""
+    voice_spec: str = ""
+    kind: str = "intro"  # intro or outro
+
+
+@dataclass
+class ConversionPlan:
+    """Complete plan for a conversion job.
+
+    This is the output of the planning phase and input to the executor.
+    """
+
+    request: ConversionRequest
+    metadata: Dict[str, Any]
+    chapters: List[ChapterPlan]
+    intro: Optional[IntroOutroSpec] = None
+    outro: Optional[IntroOutroSpec] = None
+    output_layout: Optional[OutputLayout] = None
+    extraction: Optional[ExtractionResult] = None

abogen/application/conversion_planner.py

@@ -0,0 +1,393 @@
+"""Unified conversion planner.
+
+Pure functions that take a ConversionRequest and produce a ConversionPlan.
+No side effects, no I/O — all complexity from both UIs in one place.
+
+This is Stage 2 of the conversion flow unification plan.
+"""
+
+from __future__ import annotations
+
+import logging
+from typing import Any, Dict, List, Optional, Tuple
+
+from abogen.application.conversion_models import (
+    ChapterPlan,
+    ConversionPlan,
+    IntroOutroSpec,
+    SegmentPlan,
+)
+from abogen.application.conversion_request import ConversionRequest
+from abogen.application.output_layout_service import resolve_output_layout
+from abogen.domain.chapter_overrides import apply_chapter_overrides
+from abogen.domain.file_type import auto_select_relevant_chapters
+from abogen.domain.intro_outro import resolve_intro, resolve_outro
+from abogen.domain.metadata_extraction import extract_metadata_for_file
+from abogen.domain.metadata_merge import merge_metadata
+from abogen.domain.voice_markers import split_text_by_voice_markers
+
+
+def build_conversion_plan(request: ConversionRequest) -> ConversionPlan:
+    """Build a complete conversion plan from a request.
+
+    This is the single entry point that both UIs will call.
+    It handles all the planning logic that was previously duplicated
+    in both PyQt and WebUI conversion runners.
+
+    Args:
+        request: Normalized conversion request
+
+    Returns:
+        ConversionPlan with all chapters, segments, and output layout
+
+    Raises:
+        ValueError: If request is invalid (no source, no chapters, etc.)
+    """
+    # 1. Extract and validate source
+    source_text = _extract_source_text(request)
+    if not source_text or not source_text.strip():
+        raise ValueError("No text content to convert")
+
+    # 2. Extract metadata
+    metadata, extraction = _extract_metadata(request)
+
+    # 3. Parse chapters
+    raw_chapters = _parse_chapters(source_text, request)
+
+    # 4. Apply chapter selection/overrides
+    selected_chapters = _apply_selection(raw_chapters, request)
+
+    # 5. Build segments for each chapter
+    chapters = _build_chapters(selected_chapters, request)
+
+    # 6. Build intro/outro
+    intro, outro = _build_intro_outro(metadata, request)
+
+    # 7. Resolve output layout
+    output_layout = resolve_output_layout(request)
+
+    logging.info(
+        "[planner] Plan built: chapters=%d intro=%s outro=%s",
+        len(chapters),
+        bool(intro and intro.enabled),
+        bool(outro and outro.enabled),
+    )
+
+    return ConversionPlan(
+        request=request,
+        metadata=metadata,
+        chapters=chapters,
+        intro=intro,
+        outro=outro,
+        output_layout=output_layout,
+        extraction=extraction,
+    )
+
+
+def _extract_source_text(request: ConversionRequest) -> Optional[str]:
+    """Extract text from request source."""
+    from abogen.subtitle_utils import clean_text
+
+    if request.direct_text:
+        text = clean_text(request.direct_text)
+    elif request.source_path and request.source_path.exists():
+        encoding = "utf-8"
+        try:
+            with open(request.source_path, "r", encoding=encoding, errors="replace") as f:
+                text = f.read()
+        except Exception:
+            return None
+        text = clean_text(text)
+    else:
+        return None
+
+    # Apply word substitutions if configured
+    if request.word_substitution:
+        from abogen.word_substitution import apply_word_substitutions
+
+        ws = request.word_substitution
+        text = apply_word_substitutions(
+            text,
+            ws.substitutions_list,
+            ws.case_sensitive,
+            ws.replace_caps,
+            ws.replace_numerals,
+            ws.fix_punctuation,
+        )
+
+    return text
+
+
+def _extract_metadata(
+    request: ConversionRequest,
+) -> Tuple[Dict[str, Any], Optional[Any]]:
+    """Extract metadata from source file.
+
+    Returns (metadata, extraction) tuple.
+    """
+    if request.direct_text:
+        return dict(request.metadata_tags), None
+
+    if request.source_path and request.source_path.exists():
+        try:
+            extraction = extract_metadata_for_file(
+                str(request.source_path), is_direct_text=False
+            )
+            metadata = dict(extraction.metadata) if extraction.metadata else {}
+        except Exception:
+            extraction = None
+            metadata = {}
+        metadata = merge_metadata(metadata, request.metadata_tags)
+        return metadata, extraction
+
+    return dict(request.metadata_tags), None
+
+
+def _parse_chapters(
+    source_text: str, request: ConversionRequest
+) -> List[Tuple[str, str, str]]:
+    """Parse source text into raw chapters.
+
+    Returns list of (title, body_text, default_voice) tuples.
+    """
+    from abogen.domain.text_chapters import parse_chapters_from_text
+
+    # Text is already cleaned in _extract_source_text, so clean=False here
+    chapters = parse_chapters_from_text(source_text, default_title="text", clean=False)
+
+    # Default voice from request
+    default_voice = request.voice or "M1"
+
+    return [(title, text, default_voice) for title, text in chapters]
+
+
+def _apply_selection(
+    raw_chapters: List[Tuple[str, str, str]], request: ConversionRequest
+) -> List[Tuple[str, str, str]]:
+    """Apply chapter selection and overrides."""
+    from abogen.text_extractor import ExtractedChapter
+
+    # Convert to ExtractedChapter objects for auto_select_relevant_chapters
+    extracted = [
+        ExtractedChapter(title=title, text=text)
+        for title, text, _ in raw_chapters
+    ]
+
+    # If user specified chapters, apply overrides
+    chapter_chunk = request.chapter_chunk
+    if chapter_chunk and chapter_chunk.chapter_overrides:
+        selected, _, diagnostics = apply_chapter_overrides(extracted, chapter_chunk.chapter_overrides)
+        if selected:
+            # Map back to (title, text, voice) tuples
+            result = []
+            for ch in selected:
+                # Find matching original chapter to get voice
+                voice = request.voice or "M1"
+                for orig_title, orig_text, orig_voice in raw_chapters:
+                    if orig_title == ch.title:
+                        voice = orig_voice
+                        break
+                result.append((ch.title, ch.text or "", voice))
+            return result
+        # If no chapters selected, fall through to auto-selection
+
+    # Auto-select relevant chapters
+    from abogen.domain.file_type import infer_file_type
+
+    file_type = infer_file_type(request.source_path) if request.source_path else "text"
+    result = auto_select_relevant_chapters(extracted, file_type)
+    filtered = result.kept
+
+    if filtered:
+        # Map back to (title, text, voice) tuples
+        result = []
+        for ch in filtered:
+            voice = request.voice or "M1"
+            for orig_title, orig_text, orig_voice in raw_chapters:
+                if orig_title == ch.title:
+                    voice = orig_voice
+                    break
+            result.append((ch.title, ch.text or "", voice))
+        return result
+
+    # Fall back to all chapters
+    return raw_chapters
+
+
+def _build_chapters(
+    selected_chapters: List[Tuple[str, str, str]], request: ConversionRequest
+) -> List[ChapterPlan]:
+    """Build ChapterPlan with SegmentPlan for each chapter."""
+    from abogen.domain.chapter_titles import normalize_chapter_opening_caps
+
+    chapters = []
+
+    for idx, (title, body_text, default_voice) in enumerate(selected_chapters, 1):
+        # Apply caps normalization to body text if enabled
+        if request.normalize_chapter_opening_caps and body_text:
+            body_text, _ = normalize_chapter_opening_caps(body_text)
+
+        # Build segments for this chapter (idx is 1-based, chunks use 0-based)
+        segments = _build_segments(body_text, default_voice, request, chapter_index=idx - 1)
+
+        chapter = ChapterPlan(
+            index=idx,
+            title=title,
+            original_title=title,
+            body_text=body_text,
+            segments=segments,
+            voice_spec=default_voice,
+        )
+        chapters.append(chapter)
+
+    return chapters
+
+
+def _build_segments(
+    body_text: str, default_voice: str, request: ConversionRequest,
+    chapter_index: int = 0,
+) -> List[SegmentPlan]:
+    """Build SegmentPlan list for a chapter's body text.
+
+    Handles voice markers (PyQt) and chunks (WebUI).
+    """
+    segments = []
+
+    # Check for chunks (WebUI style)
+    chapter_chunk = request.chapter_chunk
+    if chapter_chunk and chapter_chunk.chunks:
+        # Group chunks by chapter index
+        from abogen.domain.chunk_utils import group_chunks_by_chapter
+
+        chunk_groups = group_chunks_by_chapter(chapter_chunk.chunks)
+        chunks_for_chapter = chunk_groups.get(chapter_index, [])
+
+        for chunk_idx, chunk in enumerate(chunks_for_chapter):
+            chunk_text = chunk.get("normalized_text") or chunk.get("text", "")
+            if not chunk_text or not chunk_text.strip():
+                continue
+
+            chunk_voice = _resolve_chunk_voice(chunk, default_voice, request)
+            speaker_id = chunk.get("speaker_id", "narrator")
+
+            segments.append(
+                SegmentPlan(
+                    text=chunk_text.strip(),
+                    voice_spec=chunk_voice,
+                    kind="body",
+                    speaker_id=speaker_id,
+                    chunk_id=chunk.get("id"),
+                    chunk_index=chunk.get("chunk_index", chunk_idx),
+                    level=chunk.get("level", chapter_chunk.chunk_level),
+                    source="chunk",
+                )
+            )
+        return segments
+
+    # Check for voice markers (PyQt style)
+    # Detect markers even if validation fails (voice names may not be loaded yet)
+    from abogen.domain.voice_markers import _VOICE_MARKER_SEARCH_PATTERN
+
+    has_voice_markers = bool(_VOICE_MARKER_SEARCH_PATTERN.search(body_text))
+    voice_segments, last_voice, valid_count, invalid_count = split_text_by_voice_markers(
+        body_text, default_voice
+    )
+
+    if has_voice_markers or (len(voice_segments) > 1):
+        # Voice markers were used
+        for voice_name, segment_text in voice_segments:
+            if not segment_text or not segment_text.strip():
+                continue
+            segments.append(
+                SegmentPlan(
+                    text=segment_text.strip(),
+                    voice_spec=voice_name,
+                    kind="body",
+                    source="voice_marker",
+                )
+            )
+        return segments
+
+    # No voice markers — single segment for entire body
+    if body_text and body_text.strip():
+        segments.append(
+            SegmentPlan(
+                text=body_text.strip(),
+                voice_spec=default_voice,
+                kind="body",
+                source="chapter",
+            )
+        )
+
+    return segments
+
+
+def _resolve_chunk_voice(
+    chunk: Dict[str, Any], default_voice: str, request: ConversionRequest
+) -> str:
+    """Resolve voice for a chunk."""
+    # Check for speaker-based voice
+    speaker_id = chunk.get("speaker_id", "narrator")
+    speakers = request.chapter_chunk.speakers if request.chapter_chunk else {}
+    if speaker_id and speaker_id != "narrator" and speakers:
+        speaker_config = speakers.get(speaker_id, {})
+        if isinstance(speaker_config, dict):
+            voice = speaker_config.get("voice")
+            if voice:
+                return voice
+
+    # Check for direct voice field
+    voice = chunk.get("voice")
+    if voice:
+        return voice
+
+    return default_voice
+
+
+def _build_intro_outro(
+    metadata: Dict[str, Any], request: ConversionRequest
+) -> Tuple[Optional[IntroOutroSpec], Optional[IntroOutroSpec]]:
+    """Build intro and outro specs."""
+    intro_spec = None
+    outro_spec = None
+
+    # Intro
+    if request.read_title_intro:
+        resolved = resolve_intro(
+            metadata,
+            request.original_filename,
+            True,
+            request.voice or "M1",
+            request.voice or "M1",
+            [],
+        )
+        if resolved.enabled:
+            intro_spec = IntroOutroSpec(
+                enabled=True,
+                text=resolved.text,
+                voice_spec=resolved.voice_spec,
+                kind="intro",
+            )
+
+    # Outro
+    if request.read_closing_outro:
+        resolved = resolve_outro(
+            metadata,
+            request.original_filename,
+            True,
+            request.voice or "M1",
+            request.voice or "M1",
+            [],
+        )
+        if resolved.enabled:
+            outro_spec = IntroOutroSpec(
+                enabled=True,
+                text=resolved.text,
+                voice_spec=resolved.voice_spec,
+                kind="outro",
+            )
+
+    return intro_spec, outro_spec
+
+
+# Output layout resolution is now in application/output_layout_service.py

abogen/application/conversion_ports.py

@@ -0,0 +1,112 @@
+"""Ports / interfaces for the conversion service.
+
+These protocols define how the conversion service communicates with
+the outside world (UI, TTS backends, voice resolvers).
+
+The service ONLY depends on these interfaces, never on concrete
+implementations (PyQt signals, Flask Job, etc.).
+"""
+
+from __future__ import annotations
+
+from dataclasses import dataclass
+from typing import Any, Protocol
+
+
+class ConversionCancelled(Exception):
+    """Raised when conversion is cancelled by user."""
+    pass
+
+
+class ConversionEvents(Protocol):
+    """UI-specific actions the conversion service delegates back to the caller.
+
+    Implementations:
+    - PyQt: emits signals (log_updated, progress_updated, etc.)
+    - WebUI: updates Job attributes (job.add_log, job.progress, etc.)
+    """
+
+    def log(self, message: str, level: str = "info") -> None:
+        """Log a message to the UI."""
+        ...
+
+    def progress(self, processed: int, total: int, etr: str) -> None:
+        """Update progress display."""
+        ...
+
+    def check_cancelled(self) -> None:
+        """Check if conversion was cancelled.
+
+        Should raise ConversionCancelled (or UI-specific exception)
+        if cancellation is requested. Normal return means "continue".
+        """
+        ...
+
+
+class PipelineProvider(Protocol):
+    """Provides access to TTS backends (Kokoro, SuperTonic, etc.).
+
+    Implementations:
+    - PyQt: wraps self.backend (single pipeline)
+    - WebUI: wraps PipelinePool (multi-provider)
+    """
+
+    def get(self, provider: str, language: str, use_gpu: bool) -> Any:
+        """Get a TTS backend instance."""
+        ...
+
+    def dispose_all(self) -> None:
+        """Dispose all backend resources."""
+        ...
+
+
+@dataclass
+class ResolvedVoice:
+    """A resolved voice ready for TTS synthesis."""
+
+    provider: str
+    resolved_spec: str
+    voice: Any  # loaded voice tensor or name
+    speed: float
+    supertonic_steps: int
+
+
+class VoiceResolver(Protocol):
+    """Resolves voice specs into loaded voice objects.
+
+    Implementations:
+    - PyQt: wraps load_voice_cached + VoiceCache
+    - WebUI: wraps resolve_voice_choice + PipelinePool + VoiceCache
+    """
+
+    def resolve(self, voice_spec: str) -> ResolvedVoice:
+        """Resolve a voice spec into a loaded voice."""
+        ...
+
+
+class SubtitleWriter(Protocol):
+    """Writes subtitle entries to a file."""
+
+    def open(self) -> None:
+        """Open the subtitle file for writing."""
+        ...
+
+    def write_entry(self, start: float, end: float, text: str) -> None:
+        """Write a single subtitle entry."""
+        ...
+
+    def close(self) -> None:
+        """Close the subtitle file."""
+        ...
+
+
+class AudioSink(Protocol):
+    """Writes audio data to a file."""
+
+    def write(self, audio: Any) -> None:
+        """Write audio samples to the sink."""
+        ...
+
+    def close(self) -> None:
+        """Close the audio file."""
+        ...

abogen/application/conversion_request.py

@@ -0,0 +1,155 @@
+"""ConversionRequest — normalized input for a conversion job.
+
+This is NOT a WebUI Job and NOT a PyQt ConversionThread state.
+It describes the TASK, not the UI.
+
+UI adapters are responsible for converting their respective state
+into a ConversionRequest before calling ConversionService.run().
+"""
+
+from __future__ import annotations
+
+import dataclasses
+from dataclasses import dataclass, field
+from pathlib import Path
+from typing import Any, Dict, List, Optional
+
+from abogen.application.conversion_config import (
+    ChapterChunkConfig,
+    CoverConfig,
+    Epub3ExportConfig,
+    PronunciationConfig,
+    SaveConfig,
+    SubtitleConfig,
+    SubtitleInputConfig,
+    WordSubstitutionConfig,
+)
+from abogen.domain.enums import Language, OutputFormat
+
+
+class ConversionRequestError(ValueError):
+    """Raised when ConversionRequest has invalid field values."""
+
+
+# Numeric field constraints: attr -> (min, max)
+_NUMERIC_CONSTRAINTS: dict[str, tuple[float, float | None]] = {
+    "speed": (0.5, 3.0),
+    "supertonic_total_steps": (2, 15),
+    "silence_between_chapters": (0.0, None),
+    "chapter_intro_delay": (0.0, None),
+}
+
+
+@dataclass
+class ConversionRequest:
+    """Normalized request for a conversion job.
+
+    Only contains fields that describe the conversion task itself.
+    UI-only fields (display, logging, user prompts) stay in adapters.
+
+    Feature toggles use config objects (None = disabled):
+    - word_substitution, subtitle_input, chapter_chunk, epub3_export
+    - pronunciation (raw data, compiled by app layer)
+    - subtitle, save, cover (grouped parameters)
+
+    Validation runs on creation via __post_init__:
+    - None values → replaced with field default (from declaration)
+    - Numeric fields → clamped to valid range
+    """
+
+    # --- Source ---
+    source_path: Optional[Path] = None
+    direct_text: Optional[str] = None
+    original_filename: str = ""
+
+    # --- TTS Settings ---
+    language: Language = Language.EN_US
+    tts_provider: str = "kokoro"
+    voice: str = "M1"
+    voice_profile: Optional[str] = None
+    speed: float = 1.0
+    use_gpu: bool = True
+    supertonic_total_steps: int = 5
+
+    # --- Output Format ---
+    output_format: OutputFormat = OutputFormat.WAV
+
+    # --- Timing ---
+    silence_between_chapters: float = 2.0
+    chapter_intro_delay: float = 0.0
+
+    # --- Content Processing ---
+    replace_single_newlines: bool = False
+    read_title_intro: bool = False
+    read_closing_outro: bool = True
+    auto_prefix_chapter_titles: bool = True
+    normalize_chapter_opening_caps: bool = False
+
+    # --- Metadata ---
+    metadata_tags: Dict[str, Any] = field(default_factory=dict)
+
+    # --- Grouped configs ---
+    subtitle: SubtitleConfig = field(default_factory=SubtitleConfig)
+    save: SaveConfig = field(default_factory=SaveConfig)
+    cover: CoverConfig = field(default_factory=CoverConfig)
+    pronunciation: PronunciationConfig = field(default_factory=PronunciationConfig)
+
+    # --- Feature configs (None = disabled) ---
+    epub3_export: Optional[Epub3ExportConfig] = None
+    word_substitution: Optional[WordSubstitutionConfig] = None
+    subtitle_input: Optional[SubtitleInputConfig] = None
+    chapter_chunk: Optional[ChapterChunkConfig] = None
+
+    def __post_init__(self) -> None:
+        """Resolve None → default, then validate and clamp."""
+        _apply_none_defaults(self)
+        if not self.tts_provider:
+            self.tts_provider = "kokoro"
+        _coerce_enums(self)
+        _clamp_numerics(self)
+
+
+def _apply_none_defaults(obj: ConversionRequest) -> None:
+    """Replace None values with field defaults from dataclass declaration."""
+    for f in dataclasses.fields(obj):
+        if getattr(obj, f.name) is not None:
+            continue
+        if f.default is not dataclasses.MISSING:
+            setattr(obj, f.name, f.default)
+        elif f.default_factory is not dataclasses.MISSING:
+            setattr(obj, f.name, f.default_factory())
+
+
+# Enum fields that accept string coercion: attr -> (enum_class, fallback)
+_ENUM_COERCIONS: dict[str, tuple[type, Any]] = {
+    "language": (Language, Language.EN_US),
+    "output_format": (OutputFormat, OutputFormat.WAV),
+}
+
+
+def _coerce_enums(obj: ConversionRequest) -> None:
+    """Coerce string values to their expected enum types."""
+    for attr, (enum_cls, fallback) in _ENUM_COERCIONS.items():
+        val = getattr(obj, attr)
+        if isinstance(val, enum_cls):
+            continue
+        try:
+            setattr(obj, attr, enum_cls.from_str(str(val)))
+        except (ValueError, AttributeError):
+            setattr(obj, attr, fallback)
+
+
+def _clamp_numerics(obj: ConversionRequest) -> None:
+    """Clamp numeric fields to valid ranges."""
+    for attr, (min_v, max_v) in _NUMERIC_CONSTRAINTS.items():
+        val = getattr(obj, attr)
+        if val is None:
+            continue
+        if not isinstance(val, (int, float)):
+            raise ConversionRequestError(
+                f"{attr} must be a number, got {type(val).__name__}"
+            )
+        clamped = max(min_v, float(val))
+        if max_v is not None:
+            clamped = min(max_v, clamped)
+        setattr(obj, attr, clamped)

abogen/application/conversion_result.py

@@ -0,0 +1,50 @@
+"""ConversionResult — output of a successful conversion.
+
+Returned by ConversionService.run() after all synthesis and finalization.
+UI adapters consume this to update their respective state (Job, signals, etc.).
+"""
+
+from __future__ import annotations
+
+from dataclasses import dataclass, field
+from pathlib import Path
+from typing import Any, Dict, List, Optional
+
+
+@dataclass
+class ConversionResult:
+    """Output of a successful conversion job."""
+
+    # --- Primary outputs ---
+    audio_path: Optional[Path] = None
+    subtitle_paths: List[Path] = field(default_factory=list)
+    chapter_paths: List[Path] = field(default_factory=list)
+
+    # --- Markers (for metadata/audiobookshelf) ---
+    chapter_markers: List[Dict[str, Any]] = field(default_factory=list)
+    chunk_markers: List[Dict[str, Any]] = field(default_factory=list)
+
+    # --- Metadata ---
+    metadata: Dict[str, Any] = field(default_factory=dict)
+
+    # --- Artifacts ---
+    artifacts: Dict[str, Path] = field(default_factory=dict)
+    project_root: Optional[Path] = None
+    epub_path: Optional[Path] = None
+
+    # --- Stats ---
+    total_chapters: int = 0
+    total_segments: int = 0
+    total_characters: int = 0
+
+    # --- Override usage tracking ---
+    usage_counter: Dict[str, int] = field(default_factory=dict)
+
+
+@dataclass
+class ConversionError:
+    """Error information when conversion fails."""
+
+    message: str
+    details: Optional[str] = None
+    is_cancelled: bool = False

abogen/application/conversion_service.py

@@ -0,0 +1,250 @@
+"""ConversionService — main orchestrator for the conversion flow.
+
+Ties together planner, executor, and finalizers into a single entry point.
+Both UIs (PyQt, WebUI) call ConversionService.run() to execute a conversion.
+
+Responsibilities:
+- Prepare TTSContext (normalization settings, pronunciation rules)
+- Build ConversionPlan via planner
+- Execute conversion via executor
+- Handle lifecycle (cleanup, error handling)
+- Return ConversionResult
+
+The service NEVER imports from PyQt or WebUI.
+"""
+
+from __future__ import annotations
+
+import logging
+from collections import defaultdict
+from typing import Any, Dict
+
+from abogen.application.conversion_executor import execute_conversion
+from abogen.application.conversion_models import ConversionPlan
+from abogen.application.conversion_planner import build_conversion_plan
+from abogen.application.conversion_ports import ConversionEvents
+from abogen.application.conversion_request import ConversionRequest
+from abogen.application.conversion_result import ConversionResult
+from abogen.domain.normalization import build_tts_context
+
+
+def run_conversion(
+    request: ConversionRequest,
+    events: ConversionEvents,
+) -> ConversionResult:
+    """Execute a conversion request and return the result.
+
+    This is the single entry point for both UIs. It orchestrates:
+    1. Voice infrastructure setup (pool, cache, resolver)
+    2. TTS context preparation
+    3. Conversion planning
+    4. Conversion execution
+    5. Resource cleanup
+
+    Args:
+        request: Normalized conversion request
+        events: UI-specific callbacks (log, progress, check_cancelled)
+
+    Returns:
+        ConversionResult with paths and markers
+
+    Raises:
+        ConversionCancelled: If conversion was cancelled
+        ValueError: If request is invalid
+        Exception: On TTS or I/O errors
+    """
+    from abogen.domain.pipeline_factory import PipelinePool
+    from abogen.domain.voice_loader import VoiceCache
+
+    pool = PipelinePool()
+    voice_cache = VoiceCache()
+
+    try:
+        # Stage 0: Create voice resolver
+        events.log("Preparing conversion pipeline")
+        logging.info(
+            "[app] run_conversion: provider=%s language=%s voice=%s speed=%.2f",
+            request.tts_provider, request.language, request.voice, request.speed,
+        )
+        resolver = _create_voice_resolver(request, pool, voice_cache)
+
+        # Stage 1: Prepare TTS context
+        usage_counter: Dict[str, int] = defaultdict(int)
+        tts_context = build_tts_context(
+            language=request.language,
+            subtitle=request.subtitle,
+            pronunciation=request.pronunciation,
+            usage_counter=usage_counter,
+            log_callback=lambda level, msg: events.log(msg, level=level),
+        )
+
+        # Stage 2: Build conversion plan
+        events.log("Building conversion plan")
+        plan = build_conversion_plan(request)
+
+        # Stage 3: Execute conversion
+        events.log("Starting conversion")
+        result = execute_conversion(
+            plan=plan,
+            events=events,
+            pipeline_provider=pool,
+            voice_resolver=resolver,
+            tts_context=tts_context,
+        )
+
+        # Propagate usage counter to result
+        result.usage_counter = dict(usage_counter)
+
+        # Stage 4: Finalize (m4b metadata embedding, EPUB3 generation)
+        _finalize(request, result, plan, events)
+
+        events.log("Conversion complete")
+        logging.info("[app] run_conversion completed successfully")
+        return result
+
+    except Exception as e:
+        events.log(f"Conversion failed: {e}", level="error")
+        logging.exception("[app] run_conversion failed: %s", e)
+        raise
+    finally:
+        pool.dispose_all()
+        voice_cache.clear()
+        from abogen.application.cleanup import flush_cuda
+        flush_cuda()
+
+
+def _create_voice_resolver(
+    request: ConversionRequest,
+    pool: Any,
+    cache: Any,
+) -> Any:
+    """Create AppVoiceResolver with loaded profiles.
+
+    Loads voice profiles from disk, normalizes them, and creates
+    an AppVoiceResolver that can resolve voice specs into loaded voices.
+    """
+    from abogen.application.voice_resolver import AppVoiceResolver
+    from abogen.voice_profiles import load_profiles, normalize_profile_entry
+
+    try:
+        profiles = load_profiles()
+    except Exception:
+        profiles = {}
+
+    normalized_profiles: Dict[str, Dict[str, Any]] = {}
+    for name, entry in (profiles or {}).items():
+        normalized = normalize_profile_entry(entry)
+        if normalized:
+            normalized_profiles[str(name)] = normalized
+
+    return AppVoiceResolver(request, normalized_profiles, pool, cache)
+
+
+def _finalize(
+    request: ConversionRequest,
+    result: ConversionResult,
+    plan: ConversionPlan,
+    events: ConversionEvents,
+) -> None:
+    """Post-conversion finalization (m4b metadata embedding, EPUB3 generation, etc.)."""
+    from abogen.domain.enums import OutputFormat
+
+    # m4b metadata embedding
+    if (
+        result.audio_path
+        and request.output_format == OutputFormat.M4B
+    ):
+
+        from abogen.infrastructure.exporters import ExportService
+
+        export_svc = ExportService()
+
+        try:
+            export_svc.embed_m4b_metadata(
+                audio_path=result.audio_path,
+                metadata=result.metadata or {},
+                chapters=result.chapter_markers or [],
+                cover=request.cover,
+                log_callback=lambda msg, level="info": events.log(msg, level=level),
+            )
+        except Exception as exc:
+            events.log(f"Failed to embed m4b metadata: {exc}", level="error")
+            raise RuntimeError(f"Failed to embed m4b metadata: {exc}") from exc
+
+    # EPUB3 generation
+    if request.epub3_export and plan.extraction:
+        audio_asset = result.audio_path
+        if not audio_asset and result.chapter_paths:
+            audio_asset = result.chapter_paths[0]
+
+        if audio_asset:
+            try:
+
+                from abogen.epub3.exporter import build_epub3_package
+
+                epub_root = result.project_root or plan.output_layout.parent_dir
+                from abogen.domain.output_paths import build_output_path
+
+                epub_output_path = build_output_path(epub_root, request.original_filename, "epub")
+                events.log("Generating EPUB 3 package...")
+                epub_path = build_epub3_package(
+                    output_path=epub_output_path,
+                    book_id=request.epub3_export.book_id,
+                    extraction=plan.extraction,
+                    metadata_tags=result.metadata or {},
+                    chapter_markers=result.chapter_markers or [],
+                    chunk_markers=result.chunk_markers or [],
+                    chunks=request.chapter_chunk.chunks if request.chapter_chunk else [],
+                    audio_path=audio_asset,
+                    speaker_mode=request.chapter_chunk.speaker_mode if request.chapter_chunk else "single",
+                    cover=request.cover,
+                )
+                result.epub_path = epub_path
+                result.artifacts["epub3"] = epub_path
+                events.log(f"EPUB 3 package created at {epub_path}")
+            except Exception as exc:
+                events.log(f"Failed to generate EPUB 3: {exc}", level="error")
+        else:
+            events.log("Skipped EPUB 3 generation: audio output unavailable.", level="warning")
+
+    # Build metadata payload and write metadata.json
+    if plan.output_layout and plan.output_layout.metadata_dir:
+        from abogen.domain.metadata_helpers import build_metadata_payload
+
+        metadata_payload = build_metadata_payload(
+            metadata=result.metadata,
+            chapter_markers=result.chapter_markers,
+            chunk_markers=result.chunk_markers,
+            chunk_level=request.chapter_chunk.chunk_level if request.chapter_chunk else None,
+            speaker_mode=request.chapter_chunk.speaker_mode if request.chapter_chunk else None,
+            speakers=request.chapter_chunk.speakers if request.chapter_chunk else None,
+            generate_epub3=bool(request.epub3_export),
+        )
+
+        metadata_dir = plan.output_layout.metadata_dir
+        metadata_dir.mkdir(parents=True, exist_ok=True)
+        metadata_file = metadata_dir / "metadata.json"
+
+        import json
+
+        metadata_file.write_text(json.dumps(metadata_payload, indent=2), encoding="utf-8")
+        result.artifacts["metadata"] = metadata_file
+        events.log(f"Metadata written to {metadata_file}")
+
+    # Record override usage
+    if result.usage_counter:
+        try:
+            from abogen.normalization_settings import record_override_usage
+
+            record_override_usage(result.usage_counter)
+        except Exception as exc:
+            events.log(f"Failed to record override usage: {exc}", level="debug")
+
+    # Post-conversion hooks (Audiobookshelf, etc.)
+    from abogen.application.integration_hooks import PostConversionHooks
+
+    hooks = PostConversionHooks()
+    hooks.run(request, result, events)
+
+
+

abogen/application/integration_hooks.py

@@ -0,0 +1,164 @@
+"""Post-conversion integration hooks.
+
+Called by ConversionService after finalization.
+Each integration is a method on PostConversionHooks — isolated, testable,
+and easy to extend with new hooks (Plex, Navidrome, etc.).
+
+The service NEVER imports from PyQt or WebUI.
+"""
+
+from __future__ import annotations
+
+import logging
+from pathlib import Path
+from typing import Any, Mapping, Optional
+
+from abogen.application.conversion_ports import ConversionEvents
+from abogen.application.conversion_request import ConversionRequest
+from abogen.application.conversion_result import ConversionResult
+from abogen.domain.metadata_helpers import (
+    build_audiobookshelf_metadata as _build_abs_metadata,
+    load_audiobookshelf_chapters as _load_abs_chapters,
+)
+from abogen.domain.settings_core import (
+    build_audiobookshelf_config,
+    coerce_bool,
+    load_audiobookshelf_config,
+    stored_integration_config,
+)
+from abogen.integrations.audiobookshelf import (
+    AudiobookshelfClient,
+    AudiobookshelfUploadError,
+)
+
+logger = logging.getLogger(__name__)
+
+
+class PostConversionHooks:
+    """Runs post-conversion integrations (Audiobookshelf, etc.).
+
+    Usage::
+
+        hooks = PostConversionHooks()
+        hooks.run(request, result, events)
+    """
+
+    def run(
+        self,
+        request: ConversionRequest,
+        result: ConversionResult,
+        events: ConversionEvents,
+    ) -> None:
+        """Run all registered post-conversion hooks."""
+        self._maybe_send_to_audiobookshelf(request, result, events)
+
+    # ------------------------------------------------------------------
+    # Audiobookshelf
+    # ------------------------------------------------------------------
+
+    def _maybe_send_to_audiobookshelf(
+        self,
+        request: ConversionRequest,
+        result: ConversionResult,
+        events: ConversionEvents,
+    ) -> None:
+        """Upload finished audiobook to Audiobookshelf if enabled."""
+        abs_settings = stored_integration_config("audiobookshelf")
+        if not abs_settings:
+            return
+
+        enabled = coerce_bool(abs_settings.get("enabled"), False)
+        auto_send = coerce_bool(abs_settings.get("auto_send"), False)
+        if not (enabled and auto_send):
+            return
+
+        config = build_audiobookshelf_config(abs_settings)
+        if config is None:
+            events.log(
+                "Audiobookshelf upload skipped: configure base URL, API token, "
+                "library ID, and folder ID first.",
+                level="warning",
+            )
+            return
+
+        audio_path = result.audio_path
+        if not audio_path or not audio_path.exists():
+            events.log(
+                "Audiobookshelf upload skipped: audio output not found.",
+                level="warning",
+            )
+            return
+
+        # Build metadata
+        filename = request.original_filename or "Audiobook"
+        lang = request.language.value if hasattr(request.language, "value") else str(request.language)
+        metadata = _build_abs_metadata(
+            result.metadata or {},
+            language=lang,
+            filename=Path(filename).stem,
+        )
+
+        # Load chapters from metadata artifact
+        chapters = None
+        if config.send_chapters:
+            metadata_artifact = result.artifacts.get("metadata")
+            if metadata_artifact:
+                metadata_path = (
+                    metadata_artifact
+                    if isinstance(metadata_artifact, Path)
+                    else Path(str(metadata_artifact))
+                )
+                chapters = _load_abs_chapters(metadata_path)
+
+        # Resolve cover
+        cover_path = None
+        if config.send_cover and request.cover and request.cover.path:
+            candidate = request.cover.path
+            if isinstance(candidate, Path) and candidate.exists():
+                cover_path = candidate
+
+        # Resolve subtitles
+        subtitles = None
+        if config.send_subtitles and result.subtitle_paths:
+            subtitles = [
+                p for p in result.subtitle_paths
+                if isinstance(p, Path) and p.exists()
+            ]
+
+        # Upload
+        client = AudiobookshelfClient(config)
+        display_title = metadata.get("title") or audio_path.stem
+
+        try:
+            existing_items = client.find_existing_items(
+                display_title, folder_id=config.folder_id,
+            )
+        except AudiobookshelfUploadError as exc:
+            events.log(f"Audiobookshelf lookup failed: {exc}", level="error")
+            return
+
+        if existing_items:
+            events.log(
+                f"Removing existing Audiobookshelf item(s) for '{display_title}'.",
+                level="info",
+            )
+            try:
+                client.delete_items(existing_items)
+            except Exception as exc:
+                events.log(
+                    f"Failed to remove existing item(s): {exc}", level="warning",
+                )
+
+        try:
+            client.upload_audiobook(
+                audio_path,
+                metadata=metadata,
+                cover_path=cover_path,
+                chapters=chapters,
+                subtitles=subtitles,
+            )
+            events.log("Audiobookshelf upload queued.", level="info")
+        except AudiobookshelfUploadError as exc:
+            events.log(f"Audiobookshelf upload failed: {exc}", level="error")
+        except Exception as exc:
+            events.log(f"Audiobookshelf integration error: {exc}", level="error")

abogen/application/output_layout_service.py

@@ -0,0 +1,149 @@
+"""Output layout resolution service.
+
+Determines where conversion outputs (audio, subtitles, metadata) should be written.
+Extracted from conversion_planner.py as a standalone service per plan Stage 5.
+
+Responsibilities:
+- Resolve base output directory from save_mode and source_path
+- Determine base filename from original_filename
+- Find unique output path to avoid overwrites
+- Resolve project layout (audio_dir, subtitle_dir, metadata_dir)
+- Force merged output for m4b format
+- Return OutputLayout dataclass
+"""
+
+from __future__ import annotations
+
+from pathlib import Path
+
+from abogen.application.conversion_models import OutputLayout
+from abogen.application.conversion_request import ConversionRequest
+from abogen.domain.enums import OutputFormat, SaveMode, SubtitleFormat
+from abogen.domain.output_paths import (
+    resolve_project_layout,
+    resolve_unique_path,
+    sanitize_output_stem,
+)
+
+
+def resolve_output_layout(request: ConversionRequest) -> OutputLayout:
+    """Resolve output paths for a conversion request.
+
+    This is the single entry point for output path resolution,
+    used by both UIs and the conversion service.
+
+    Args:
+        request: Normalized conversion request
+
+    Returns:
+        OutputLayout with resolved paths
+    """
+    # Determine base output directory
+    if request.save.mode == SaveMode.CUSTOM_FOLDER and request.save.output_folder:
+        parent_dir = Path(request.save.output_folder)
+    elif request.source_path:
+        parent_dir = request.source_path.parent
+    else:
+        parent_dir = Path.cwd()
+
+    # Determine base name
+    if request.original_filename:
+        base_name = sanitize_output_stem(request.original_filename)
+    elif request.source_path:
+        base_name = sanitize_output_stem(request.source_path.stem)
+    else:
+        base_name = "output"
+
+    # Find unique output path
+    allowed_exts = {request.output_format, SubtitleFormat.SRT, SubtitleFormat.ASS, "vtt", "mp4", OutputFormat.M4B}
+    unique_base = resolve_unique_path(
+        parent_dir, base_name, "", allowed_extensions=allowed_exts
+    )
+
+    # Resolve project layout
+    project_root = None
+    audio_dir = parent_dir
+    subtitle_dir = None
+    metadata_dir = None
+
+    if request.save.save_as_project:
+        project_root, audio_dir, subtitle_dir, metadata_dir = resolve_project_layout(
+            original_filename=request.original_filename,
+            save_as_project=True,
+            base_dir=parent_dir,
+        )
+
+    return OutputLayout(
+        parent_dir=parent_dir,
+        project_root=project_root,
+        audio_dir=audio_dir,
+        subtitle_dir=subtitle_dir,
+        metadata_dir=metadata_dir,
+    )
+
+
+def resolve_merged_path(
+    layout: OutputLayout,
+    request: ConversionRequest,
+) -> Path:
+    """Resolve the merged output audio file path.
+
+    Args:
+        layout: Resolved output layout
+        request: Conversion request
+
+    Returns:
+        Path to the merged output file
+    """
+    base_name = sanitize_output_stem(
+        request.original_filename or "output"
+    )
+    return layout.audio_dir / f"{base_name}{request.output_format.dot_ext}"
+
+
+def resolve_chapter_path(
+    layout: OutputLayout,
+    request: ConversionRequest,
+    chapter_title: str,
+    chapter_index: int,
+) -> Path:
+    """Resolve the output path for a separate chapter file.
+
+    Args:
+        layout: Resolved output layout
+        request: Conversion request
+        chapter_title: Chapter title for filename
+        chapter_index: Chapter number (1-based)
+
+    Returns:
+        Path to the chapter output file
+    """
+    import re
+
+    slug = re.sub(r'[^\w\s-]', '', chapter_title.lower())
+    slug = re.sub(r'[\s_]+', '_', slug).strip('_')
+    if not slug:
+        slug = f"chapter_{chapter_index}"
+    filename = f"{chapter_index:02d}_{slug}.{request.save.separate_chapters_format}"
+    return layout.audio_dir / "chapters" / filename
+
+
+def should_merge_output(request: ConversionRequest) -> bool:
+    """Determine if merged output is required.
+
+    Rules:
+    - m4b format always forces merged output
+    - If save_chapters_separately is False, merged is required
+    - Otherwise, use merge_chapters_at_end setting
+
+    Args:
+        request: Conversion request
+
+    Returns:
+        True if merged output should be created
+    """
+    if request.output_format == OutputFormat.M4B:
+        return True
+    if not request.save.save_chapters_separately:
+        return True
+    return request.save.merge_chapters_at_end

abogen/application/voice_resolver.py

@@ -0,0 +1,81 @@
+"""AppVoiceResolver — voice resolution inside the application layer.
+
+Resolves voice specs into loaded voices using profiles, pipeline pool,
+and voice cache. Replaces UI-specific resolvers (WebUIVoiceResolver,
+PyQtVoiceResolver) with a single app-layer implementation.
+"""
+
+from __future__ import annotations
+
+import logging
+from typing import Any, Dict, Optional
+
+from abogen.application.conversion_ports import ResolvedVoice, VoiceResolver
+from abogen.application.conversion_request import ConversionRequest
+from abogen.domain.pipeline_factory import PipelinePool
+from abogen.domain.voice_loader import VoiceCache, resolve_voice
+from abogen.domain.voice_utils import resolve_voice_target
+
+
+class AppVoiceResolver:
+    """App-layer implementation of VoiceResolver protocol.
+
+    Uses ConversionRequest instead of Job. Loads profiles, creates
+    resolver internally — UIs don't need to manage this.
+    """
+
+    def __init__(
+        self,
+        request: ConversionRequest,
+        normalized_profiles: Dict[str, Dict[str, Any]],
+        pool: PipelinePool,
+        cache: VoiceCache,
+    ):
+        self._request = request
+        self._profiles = normalized_profiles
+        self._cache = cache
+        self._pool = pool
+
+    def resolve(self, voice_spec: str) -> ResolvedVoice:
+        """Resolve a voice spec into a loaded voice."""
+        provider, resolved, speed, steps = resolve_voice_target(
+            voice_spec,
+            self._profiles,
+            job_voice=self._request.voice,
+            job_tts_provider=self._request.tts_provider,
+            job_supertonic_total_steps=self._request.supertonic_total_steps,
+            job_speed=self._request.speed,
+        )
+
+        cache_key = f"{provider}:{resolved}" if resolved else provider
+        cached = self._cache.get(cache_key)
+        if cached is not None:
+            logging.info("[resolver] Cache hit: spec=%s -> provider=%s resolved=%s", voice_spec, provider, resolved)
+            return ResolvedVoice(
+                provider=provider,
+                resolved_spec=resolved,
+                voice=cached,
+                speed=speed,
+                supertonic_steps=steps or 0,
+            )
+
+        if provider == "kokoro":
+            kokoro_backend = self._pool.get(
+                "kokoro", self._request.language, self._request.use_gpu,
+            )
+            loaded = resolve_voice(
+                resolved, kokoro_backend, self._request.use_gpu, cache=self._cache,
+            )
+        else:
+            loaded = resolved
+
+        self._cache.set(cache_key, loaded)
+        logging.info("[resolver] Resolved: spec=%s -> provider=%s resolved=%s speed=%.2f steps=%s",
+                      voice_spec, provider, resolved, speed, steps)
+        return ResolvedVoice(
+            provider=provider,
+            resolved_spec=resolved,
+            voice=loaded,
+            speed=speed,
+            supertonic_steps=steps or 0,
+        )

abogen/book_parser.py

@@ -12,7 +12,8 @@ import fitz  # PyMuPDF
 import markdown
 
 from abogen.utils import detect_encoding
-from abogen.subtitle_utils import clean_text, calculate_text_length
+from abogen.subtitle_utils import clean_text
+from abogen.domain.text_utils import calculate_text_length
 
 # Pre-compile frequently used regex patterns
 _BRACKETED_NUMBERS_PATTERN = re.compile(r"\[\s*\d+\s*\]")

abogen/constants.py

@@ -1,4 +1,5 @@
 from abogen.utils import get_version
+from abogen.domain.enums import Language
 
 # Program Information
 PROGRAM_NAME = "abogen"
@@ -16,8 +17,22 @@ SUBTITLE_FORMATS = [
     ("ass_centered_narrow", "ASS (centered narrow)"),
 ]
 
-# Language description mapping
+# Language description mapping (Language enum → human-readable label).
 LANGUAGE_DESCRIPTIONS = {
+    Language.EN_US: "American English",
+    Language.EN_GB: "British English",
+    Language.ES: "Spanish",
+    Language.FR: "French",
+    Language.HI: "Hindi",
+    Language.IT: "Italian",
+    Language.JA: "Japanese",
+    Language.PT_BR: "Brazilian Portuguese",
+    Language.ZH: "Mandarin Chinese",
+}
+
+# Display-only mapping for kokoro codes → labels.
+# Used by voice catalog and PyQt (legacy) where kokoro codes are still present.
+KOKORO_CODE_LABELS = {
     "a": "American English",
     "b": "British English",
     "e": "Spanish",
@@ -56,82 +71,22 @@ SUPPORTED_INPUT_FORMATS = [
 ]
 
 # Supported languages for subtitle generation
-# Currently, only 'a (American English)' and 'b (British English)' are supported for subtitle generation.
+# Currently, only English (EN_US, EN_GB) are supported for subtitle generation.
 # This is because tokens that contain timestamps are not generated for other languages in the Kokoro pipeline.
 # Please refer to: https://github.com/hexgrad/kokoro/blob/6d87f4ae7abc2d14dbc4b3ef2e5f19852e861ac2/kokoro/pipeline.py
-# 383 English processing (unchanged)
-# 384 if self.lang_code in 'ab':
-SUPPORTED_LANGUAGES_FOR_SUBTITLE_GENERATION = list(LANGUAGE_DESCRIPTIONS.keys())
-
-# Voice and sample text constants
-VOICES_INTERNAL = [
-    "af_alloy",
-    "af_aoede",
-    "af_bella",
-    "af_heart",
-    "af_jessica",
-    "af_kore",
-    "af_nicole",
-    "af_nova",
-    "af_river",
-    "af_sarah",
-    "af_sky",
-    "am_adam",
-    "am_echo",
-    "am_eric",
-    "am_fenrir",
-    "am_liam",
-    "am_michael",
-    "am_onyx",
-    "am_puck",
-    "am_santa",
-    "bf_alice",
-    "bf_emma",
-    "bf_isabella",
-    "bf_lily",
-    "bm_daniel",
-    "bm_fable",
-    "bm_george",
-    "bm_lewis",
-    "ef_dora",
-    "em_alex",
-    "em_santa",
-    "ff_siwis",
-    "hf_alpha",
-    "hf_beta",
-    "hm_omega",
-    "hm_psi",
-    "if_sara",
-    "im_nicola",
-    "jf_alpha",
-    "jf_gongitsune",
-    "jf_nezumi",
-    "jf_tebukuro",
-    "jm_kumo",
-    "pf_dora",
-    "pm_alex",
-    "pm_santa",
-    "zf_xiaobei",
-    "zf_xiaoni",
-    "zf_xiaoxiao",
-    "zf_xiaoyi",
-    "zm_yunjian",
-    "zm_yunxi",
-    "zm_yunxia",
-    "zm_yunyang",
-]
+SUPPORTED_LANGUAGES_FOR_SUBTITLE_GENERATION = [Language.EN_US, Language.EN_GB]
 
 # Voice and sample text mapping
 SAMPLE_VOICE_TEXTS = {
-    "a": "This is a sample of the selected voice.",
-    "b": "This is a sample of the selected voice.",
-    "e": "Este es una muestra de la voz seleccionada.",
-    "f": "Ceci est un exemple de la voix sélectionnée.",
-    "h": "यह चयनित आवाज़ का एक नमूना है।",
-    "i": "Questo è un esempio della voce selezionata.",
-    "j": "これは選択した声のサンプルです。",
-    "p": "Este é um exemplo da voz selecionada.",
-    "z": "这是所选语音的示例。",
+    Language.EN_US: "This is a sample of the selected voice.",
+    Language.EN_GB: "This is a sample of the selected voice.",
+    Language.ES: "Este es una muestra de la voz seleccionada.",
+    Language.FR: "Ceci est un exemple de la voix sélectionnée.",
+    Language.HI: "यह चयनित आवाज़ का एक नमूना है।",
+    Language.IT: "Questo è un esempio della voce selezionata.",
+    Language.JA: "これは選択した声のサンプルです。",
+    Language.PT_BR: "Este é um exemplo da voz selecionada.",
+    Language.ZH: "这是所选语音的示例。",
 }
 
 COLORS = {

abogen/domain/audio_buffer.py

@@ -0,0 +1,239 @@
+"""Audio buffer operations for audiobook generation.
+
+This module provides core audio buffer manipulation functions including:
+- Silence generation
+- Audio mixing
+- Audio normalization
+- Audio buffer resizing
+"""
+
+from __future__ import annotations
+
+from typing import Optional
+
+import numpy as np
+
+# Standard sample rate used throughout the application
+SAMPLE_RATE = 24000
+
+
+def create_silence(duration_seconds: float) -> np.ndarray:
+    """Create a silence audio buffer.
+    
+    Args:
+        duration_seconds: Duration of silence in seconds.
+        
+    Returns:
+        Numpy array of float32 zeros with length = duration_seconds * SAMPLE_RATE.
+        Returns empty array if duration is <= 0.
+    """
+    if duration_seconds <= 0:
+        return np.array([], dtype="float32")
+    
+    samples = int(round(duration_seconds * SAMPLE_RATE))
+    if samples <= 0:
+        return np.array([], dtype="float32")
+    
+    return np.zeros(samples, dtype="float32")
+
+
+def mix_audio(
+    target: np.ndarray,
+    source: np.ndarray,
+    start_sample: int,
+    end_sample: Optional[int] = None,
+) -> np.ndarray:
+    """Mix source audio into target buffer at specified position.
+    
+    This performs additive mixing (target += source). The target buffer
+    is extended if necessary to accommodate the source audio.
+    
+    Args:
+        target: The target audio buffer to mix into.
+        source: The source audio buffer to mix.
+        start_sample: Starting sample index in target buffer.
+        end_sample: Optional end sample index. If None, calculated from source length.
+        
+    Returns:
+        The target buffer (possibly extended). If target was extended, returns new array.
+    """
+    if source.size == 0:
+        return target
+    
+    if end_sample is None:
+        end_sample = start_sample + len(source)
+    
+    # Extend target buffer if needed
+    if end_sample > len(target):
+        new_length = end_sample
+        new_target = np.concatenate([
+            target,
+            np.zeros(new_length - len(target), dtype="float32")
+        ])
+        target = new_target
+    
+    # Perform the mix (additive)
+    target[start_sample:end_sample] += source
+    return target
+
+
+def normalize_audio(
+    audio: np.ndarray,
+    target_peak: float = 1.0,
+) -> np.ndarray:
+    """Normalize audio buffer to prevent clipping.
+    
+    If the audio exceeds the target peak (default 1.0), it is scaled down
+    proportionally to prevent distortion.
+    
+    Args:
+        audio: Input audio buffer.
+        target_peak: Target maximum amplitude (default 1.0).
+        
+    Returns:
+        Normalized audio buffer (new array, original is not modified).
+    """
+    if audio.size == 0:
+        return audio.copy()
+    
+    max_amplitude = float(np.abs(audio).max())
+    
+    if max_amplitude <= target_peak:
+        return audio.copy()
+    
+    # Scale down to prevent clipping
+    scale_factor = target_peak / max_amplitude
+    return (audio * scale_factor).astype("float32")
+
+
+def ensure_buffer_size(
+    buffer: np.ndarray,
+    min_samples: int,
+) -> np.ndarray:
+    """Ensure audio buffer is at least min_samples long.
+    
+    If buffer is shorter, it is extended with zeros.
+    
+    Args:
+        buffer: Input audio buffer.
+        min_samples: Minimum required length in samples.
+        
+    Returns:
+        Buffer of at least min_samples length (new array if extended).
+    """
+    if len(buffer) >= min_samples:
+        return buffer
+    
+    new_buffer = np.zeros(min_samples, dtype="float32")
+    new_buffer[:len(buffer)] = buffer
+    return new_buffer
+
+
+def concatenate_audio(*buffers: np.ndarray) -> np.ndarray:
+    """Concatenate multiple audio buffers.
+    
+    Args:
+        *buffers: Audio buffers to concatenate.
+        
+    Returns:
+        Single concatenated audio buffer.
+    """
+    non_empty = [b for b in buffers if b.size > 0]
+    if not non_empty:
+        return np.array([], dtype="float32")
+    return np.concatenate(non_empty)
+
+
+def audio_duration(audio: np.ndarray, sample_rate: int = SAMPLE_RATE) -> float:
+    """Calculate duration of audio buffer in seconds.
+    
+    Args:
+        audio: Audio buffer.
+        sample_rate: Sample rate in Hz (default SAMPLE_RATE).
+        
+    Returns:
+        Duration in seconds.
+    """
+    return len(audio) / sample_rate
+
+
+def samples_for_duration(duration_seconds: float, sample_rate: int = SAMPLE_RATE) -> int:
+    """Calculate number of samples for a given duration.
+    
+    Args:
+        duration_seconds: Duration in seconds.
+        sample_rate: Sample rate in Hz (default SAMPLE_RATE).
+        
+    Returns:
+        Number of samples (rounded to nearest integer), or 0 if duration is <= 0.
+    """
+    if duration_seconds <= 0:
+        return 0
+    return int(round(duration_seconds * sample_rate))
+
+
+def fit_audio_to_duration(
+    audio: np.ndarray,
+    target_duration: float,
+    sample_rate: int = SAMPLE_RATE,
+) -> np.ndarray:
+    """Pad or trim audio to match target duration.
+
+    Args:
+        audio: Input audio buffer.
+        target_duration: Desired duration in seconds.
+        sample_rate: Sample rate in Hz.
+
+    Returns:
+        Audio buffer of exact length target_duration * sample_rate.
+    """
+    target_samples = int(target_duration * sample_rate)
+    if len(audio) < target_samples:
+        padding = np.zeros(target_samples - len(audio), dtype="float32")
+        return np.concatenate([audio, padding])
+    return audio[:target_samples]
+
+
+def ffmpeg_time_stretch(
+    audio: np.ndarray,
+    speed_factor: float,
+    sample_rate: int = SAMPLE_RATE,
+) -> np.ndarray:
+    """Time-stretch audio using FFmpeg's atempo filter.
+
+    Args:
+        audio: Input audio buffer (float32).
+        speed_factor: Speed multiplier (>1.0 = faster).
+        sample_rate: Sample rate in Hz.
+
+    Returns:
+        Time-stretched audio buffer.
+    """
+    import math
+    import subprocess
+
+    import static_ffmpeg
+
+    if speed_factor <= 1.0 or audio.size == 0:
+        return audio
+
+    static_ffmpeg.add_paths()
+    num_stages = max(1, int(math.ceil(math.log(speed_factor) / math.log(2.0))))
+    tempo = speed_factor ** (1.0 / num_stages)
+    filter_str = ",".join([f"atempo={tempo:.6f}"] * num_stages)
+
+    proc = subprocess.Popen(
+        [
+            "ffmpeg", "-y",
+            "-f", "f32le", "-ar", str(sample_rate), "-ac", "1",
+            "-i", "pipe:0",
+            "-filter:a", filter_str,
+            "-f", "f32le", "-ar", str(sample_rate), "-ac", "1",
+            "pipe:1",
+        ],
+        stdin=subprocess.PIPE,
+        stdout=subprocess.PIPE,
+        stderr=subprocess.PIPE,
+    )
+    out, _ = proc.communicate(input=audio.tobytes())
+    return np.frombuffer(out, dtype="float32")

abogen/domain/audio_helpers.py

@@ -0,0 +1,118 @@
+"""Audio helper utilities.
+
+Functions for building ffmpeg commands, converting audio formats,
+and applying chapter metadata to MP4 files.
+"""
+
+from __future__ import annotations
+
+from pathlib import Path
+from typing import Any, Dict, List, Optional
+
+import numpy as np
+
+
+SAMPLE_RATE = 24000
+
+
+def build_ffmpeg_command(path: Path, fmt: str, metadata: Optional[Dict[str, str]] = None) -> list[str]:
+    from abogen.infrastructure.exporters import ExportService
+
+    base = [
+        "ffmpeg",
+        "-y",
+        "-f",
+        "f32le",
+        "-ar",
+        str(SAMPLE_RATE),
+        "-ac",
+        "1",
+        "-i",
+        "pipe:0",
+    ]
+    if fmt == "mp3":
+        base += ["-c:a", "libmp3lame", "-qscale:a", "2"]
+    elif fmt == "opus":
+        base += ["-c:a", "libopus", "-b:a", "24000"]
+    elif fmt == "m4b":
+        base += ["-c:a", "aac", "-q:a", "2", "-movflags", "+faststart+use_metadata_tags"]
+    else:
+        base += ["-c:a", "copy"]
+
+    if metadata:
+        svc = ExportService()
+        base.extend(svc._metadata_to_ffmpeg_args(metadata))
+    base.append(str(path))
+    return base
+
+
+def to_float32(audio_segment) -> np.ndarray:
+    if audio_segment is None:
+        return np.zeros(0, dtype="float32")
+
+    tensor = audio_segment
+    if hasattr(tensor, "detach"):
+        tensor = tensor.detach()
+    if hasattr(tensor, "cpu"):
+        try:
+            tensor = tensor.cpu()
+        except Exception:
+            pass
+    if hasattr(tensor, "numpy"):
+        return np.asarray(tensor.numpy(), dtype="float32").reshape(-1)
+    return np.asarray(tensor, dtype="float32").reshape(-1)
+
+
+def apply_m4b_chapters_with_mutagen(
+    audio_path: Path,
+    chapters: List[Dict[str, Any]],
+) -> bool:
+    """Apply chapter atoms to an MP4/M4B file using mutagen.
+
+    Returns True if chapters were written, False otherwise.
+    Raises ImportError if mutagen is not installed.
+    """
+    if not chapters:
+        return False
+
+    from fractions import Fraction
+    from mutagen.mp4 import MP4, MP4Chapter  # type: ignore[import]
+
+    mp4 = MP4(str(audio_path))
+
+    chapter_objects: List[MP4Chapter] = []
+    for index, entry in enumerate(sorted(chapters, key=lambda item: float(item.get("start") or 0.0))):
+        start_raw = entry.get("start")
+        if start_raw is None:
+            continue
+        try:
+            start_seconds = max(0.0, float(start_raw))
+        except (TypeError, ValueError):
+            continue
+
+        title_value = entry.get("title")
+        title_text = str(title_value) if title_value else f"Chapter {index + 1}"
+
+        start_fraction = Fraction(int(round(start_seconds * 1000)), 1000)
+        chapter_atom = MP4Chapter(start_fraction, title_text)
+
+        end_raw = entry.get("end")
+        if end_raw is not None:
+            try:
+                end_seconds = float(end_raw)
+            except (TypeError, ValueError):
+                end_seconds = None
+            if end_seconds is not None and end_seconds > start_seconds:
+                chapter_atom.end = Fraction(int(round(end_seconds * 1000)), 1000)
+
+        chapter_objects.append(chapter_atom)
+
+    if not chapter_objects:
+        return False
+
+    from typing import cast
+
+    mp4.chapters = cast(Any, chapter_objects)
+    mp4.save()
+
+    return True

abogen/domain/audio_sink.py

@@ -0,0 +1,131 @@
+"""Audio sink abstraction for unified audio output.
+
+Provides a context-manager-based abstraction for writing audio data
+to various output formats (WAV, FLAC via soundfile; compressed via ffmpeg).
+
+Usage:
+    with open_audio_sink(path, "wav") as sink:
+        sink.write(audio_data)
+"""
+
+from __future__ import annotations
+
+import os
+import subprocess
+import sys
+from dataclasses import dataclass
+from pathlib import Path
+from typing import Callable, Optional
+
+import numpy as np
+
+from abogen.domain.audio_buffer import SAMPLE_RATE
+from abogen.domain.audio_helpers import build_ffmpeg_command
+
+
+@dataclass(frozen=True)
+class AudioSink:
+    """Represents an open audio output target."""
+
+    write: Callable[[np.ndarray], None]
+    close: Callable[[], None]
+
+    def __enter__(self) -> AudioSink:
+        return self
+
+    def __exit__(self, exc_type, exc_val, exc_tb) -> None:
+        self.close()
+
+
+def _ensure_ffmpeg() -> None:
+    """Ensure static ffmpeg binaries are on PATH."""
+    import static_ffmpeg  # type: ignore
+
+    ffmpeg_cache_root = _get_ffmpeg_cache_root()
+    platform_cache = os.path.join(ffmpeg_cache_root, sys.platform)
+    os.makedirs(platform_cache, exist_ok=True)
+    try:
+        import static_ffmpeg.run as static_ffmpeg_run  # type: ignore
+
+        static_ffmpeg_run.LOCK_FILE = os.path.join(ffmpeg_cache_root, "lock.file")
+    except Exception:
+        pass
+    static_ffmpeg.add_paths(weak=True, download_dir=platform_cache)
+
+
+def _get_ffmpeg_cache_root() -> str:
+    from abogen.utils import get_internal_cache_path
+
+    return get_internal_cache_path("ffmpeg")
+
+
+def open_audio_sink(
+    path: Path,
+    fmt: str,
+    *,
+    metadata: Optional[dict[str, str]] = None,
+    cancel_check: Optional[Callable[[], bool]] = None,
+    extra_ffmpeg_args: Optional[list[str]] = None,
+    ffmpeg_cmd: Optional[list[str]] = None,
+) -> AudioSink:
+    """Open an audio output sink for writing raw float32 PCM samples.
+
+    Args:
+        path: Output file path.
+        fmt: Output format ("wav", "flac", "mp3", "opus", "m4b").
+        metadata: Optional metadata dict (ignored when ffmpeg_cmd is provided).
+        cancel_check: Optional callable; if it returns True, writes are silently skipped.
+        extra_ffmpeg_args: Optional extra args inserted after ffmpeg header (ignored when ffmpeg_cmd is provided).
+        ffmpeg_cmd: Optional pre-built ffmpeg command list (for m4b with cover art etc.).
+
+    Returns:
+        AudioSink with write() and close() methods.
+    """
+    fmt = fmt.lower()
+
+    if fmt in {"wav", "flac"}:
+        import soundfile as sf
+
+        soundfile_obj = sf.SoundFile(
+            path,
+            mode="w",
+            samplerate=SAMPLE_RATE,
+            channels=1,
+            format=fmt.upper(),
+        )
+
+        def _write_wav(data: np.ndarray) -> None:
+            if cancel_check and cancel_check():
+                return
+            soundfile_obj.write(data)
+
+        def _close_wav() -> None:
+            soundfile_obj.close()
+
+        return AudioSink(write=_write_wav, close=_close_wav)
+
+    # Compressed formats: pipe through ffmpeg
+    _ensure_ffmpeg()
+
+    if ffmpeg_cmd is not None:
+        cmd = list(ffmpeg_cmd)
+    else:
+        cmd = build_ffmpeg_command(path, fmt, metadata=metadata)
+        if extra_ffmpeg_args:
+            cmd[2:2] = extra_ffmpeg_args
+
+    process = subprocess.Popen(
+        cmd, stdin=subprocess.PIPE, stdout=subprocess.DEVNULL, stderr=subprocess.DEVNULL
+    )
+
+    def _write_compressed(data: np.ndarray) -> None:
+        if (cancel_check and cancel_check()) or process.stdin is None or process.stdin.closed:
+            return
+        process.stdin.write(data.tobytes())
+
+    def _close_compressed() -> None:
+        if process.stdin and not process.stdin.closed:
+            process.stdin.close()
+        process.wait()
+
+    return AudioSink(write=_write_compressed, close=_close_compressed)

abogen/domain/chapter_classification.py

@@ -0,0 +1,131 @@
+"""Heuristics for classifying chapters as content vs. supplements.
+
+A 'supplement' is any non-story material that a listener would typically
+skip: title page, copyright, table of contents, acknowledgements, etc.
+The scoring functions return a float; higher ⇒ more likely to be a
+supplement.  ``should_preselect_chapter`` turns that score into a
+boolean suitable for a web form default.
+"""
+
+from __future__ import annotations
+
+import re
+from typing import Any, Dict, List, Tuple
+
+# Compiled once at module load – these are immutable.
+
+_SUPPLEMENT_TITLE_PATTERNS: List[Tuple[re.Pattern[str], float]] = [
+    (re.compile(r"\btitle\s+page\b"), 3.0),
+    (re.compile(r"\bcopyright\b"), 2.4),
+    (re.compile(r"\btable\s+of\s+contents\b"), 2.8),
+    (re.compile(r"\bcontents\b"), 2.0),
+    (re.compile(r"\backnowledg(e)?ments?\b"), 2.0),
+    (re.compile(r"\bdedication\b"), 2.0),
+    (re.compile(r"\babout\s+the\s+author(s)?\b"), 2.4),
+    (re.compile(r"\balso\s+by\b"), 2.0),
+    (re.compile(r"\bpraise\s+for\b"), 2.0),
+    (re.compile(r"\bcolophon\b"), 2.2),
+    (re.compile(r"\bpublication\s+data\b"), 2.2),
+    (re.compile(r"\btranscriber'?s?\s+note\b"), 2.2),
+    (re.compile(r"\bglossary\b"), 2.2),
+    (re.compile(r"\bindex\b"), 2.0),
+    (re.compile(r"\bbibliograph(y|ies)\b"), 2.0),
+    (re.compile(r"\breferences\b"), 1.8),
+    (re.compile(r"\bappendix\b"), 1.9),
+]
+
+_CONTENT_TITLE_PATTERNS: List[re.Pattern[str]] = [
+    re.compile(r"\bchapter\b"),
+    re.compile(r"\bbook\b"),
+    re.compile(r"\bpart\b"),
+    re.compile(r"\bsection\b"),
+    re.compile(r"\bscene\b"),
+    re.compile(r"\bprologue\b"),
+    re.compile(r"\bepilogue\b"),
+    re.compile(r"\bintroduction\b"),
+    re.compile(r"\bstory\b"),
+]
+
+_SUPPLEMENT_TEXT_KEYWORDS: List[Tuple[str, float]] = [
+    ("copyright", 1.2),
+    ("all rights reserved", 1.1),
+    ("isbn", 0.9),
+    ("library of congress", 1.0),
+    ("table of contents", 1.0),
+    ("dedicated to", 0.8),
+    ("acknowledg", 0.8),
+    ("printed in", 0.6),
+    ("permission", 0.6),
+    ("publisher", 0.5),
+    ("praise for", 0.9),
+    ("also by", 0.9),
+    ("glossary", 0.8),
+    ("index", 0.8),
+    ("newsletter", 3.2),
+    ("mailing list", 2.6),
+    ("sign-up", 2.2),
+]
+
+
+def supplement_score(title: str, text: str, index: int) -> float:
+    """Return a score indicating how likely *title*/*text* is a supplement.
+
+    Higher values ⇒ more likely to be non-story material (title page,
+    copyright, acknowledgements, etc.).
+    """
+    normalized_title = (title or "").lower()
+    score = 0.0
+
+    for pattern, weight in _SUPPLEMENT_TITLE_PATTERNS:
+        if pattern.search(normalized_title):
+            score += weight
+
+    for pattern in _CONTENT_TITLE_PATTERNS:
+        if pattern.search(normalized_title):
+            score -= 2.0
+
+    stripped_text = (text or "").strip()
+    length = len(stripped_text)
+    if length <= 150:
+        score += 0.9
+    elif length <= 400:
+        score += 0.6
+    elif length <= 800:
+        score += 0.35
+
+    lowercase_text = stripped_text.lower()
+    for keyword, weight in _SUPPLEMENT_TEXT_KEYWORDS:
+        if keyword in lowercase_text:
+            score += weight
+
+    if index == 0 and score > 0:
+        score += 0.25
+
+    return score
+
+
+def should_preselect_chapter(
+    title: str,
+    text: str,
+    index: int,
+    total_count: int,
+) -> bool:
+    """Return True if the chapter should be *enabled* by default in the form.
+
+    A single chapter is always preselected.  For multi-chapter books, the
+    chapter is preselected when its supplement score is below 1.9.
+    """
+    if total_count <= 1:
+        return True
+    score = supplement_score(title, text, index)
+    return score < 1.9
+
+
+def ensure_at_least_one_chapter_enabled(chapters: List[Dict[str, Any]]) -> None:
+    """Mutate *chapters* in-place so that at least one has ``enabled=True``."""
+    if not chapters:
+        return
+    if any(chapter.get("enabled") for chapter in chapters):
+        return
+    best_index = max(range(len(chapters)), key=lambda idx: chapters[idx].get("characters", 0))
+    chapters[best_index]["enabled"] = True

abogen/domain/chapter_overrides.py

@@ -0,0 +1,92 @@
+from __future__ import annotations
+
+from typing import Any, Dict, List, Optional, Tuple
+
+from abogen.text_extractor import ExtractedChapter
+from abogen.domain.voice_utils import coerce_truthy
+
+
+def apply_chapter_overrides(
+    extracted: List[ExtractedChapter],
+    overrides: List[Dict[str, Any]],
+) -> Tuple[List[ExtractedChapter], Dict[str, str], List[str]]:
+    if not overrides:
+        return [], {}, []
+
+    selected: List[ExtractedChapter] = []
+    metadata_updates: Dict[str, str] = {}
+    diagnostics: List[str] = []
+
+    for position, payload in enumerate(overrides):
+        if not isinstance(payload, dict):
+            diagnostics.append(
+                f"Skipped chapter override at position {position + 1}: unsupported payload type {type(payload).__name__}."
+            )
+            continue
+
+        enabled = coerce_truthy(payload.get("enabled", True))
+        payload["enabled"] = enabled
+        if not enabled:
+            continue
+
+        metadata_payload = payload.get("metadata") or {}
+        if isinstance(metadata_payload, dict):
+            for key, value in metadata_payload.items():
+                if value is None:
+                    continue
+                metadata_updates[str(key)] = str(value)
+
+        base: Optional[ExtractedChapter] = None
+        idx_candidate = payload.get("index")
+        idx_normalized: Optional[int] = None
+        if isinstance(idx_candidate, int):
+            idx_normalized = idx_candidate
+        elif isinstance(idx_candidate, str):
+            try:
+                idx_normalized = int(idx_candidate)
+            except ValueError:
+                idx_normalized = None
+        if idx_normalized is not None and 0 <= idx_normalized < len(extracted):
+            base = extracted[idx_normalized]
+            payload["index"] = idx_normalized
+
+        if base is None:
+            source_title = payload.get("source_title")
+            if isinstance(source_title, str):
+                base = next((chapter for chapter in extracted if chapter.title == source_title), None)
+
+        if base is None:
+            candidate_title = payload.get("title")
+            if isinstance(candidate_title, str):
+                base = next((chapter for chapter in extracted if chapter.title == candidate_title), None)
+
+        text_override = payload.get("text")
+        if text_override is not None:
+            text_value = str(text_override)
+        elif base is not None:
+            text_value = base.text
+        else:
+            diagnostics.append(
+                f"Skipped chapter override at position {position + 1}: no text provided and no matching source chapter found."
+            )
+            continue
+
+        title_override = payload.get("title")
+        if title_override is not None:
+            title_value = str(title_override)
+        elif base is not None:
+            title_value = base.title
+        else:
+            title_value = f"Chapter {position + 1}"
+
+        if base and not payload.get("source_title"):
+            payload["source_title"] = base.title
+
+        payload["title"] = title_value
+        payload["text"] = text_value
+        payload["characters"] = len(text_value)
+        payload.setdefault("order", payload.get("order", position))
+
+        selected.append(ExtractedChapter(title=title_value, text=text_value))
+
+    return selected, metadata_updates, diagnostics

abogen/domain/chapter_titles.py

@@ -0,0 +1,204 @@
+from __future__ import annotations
+
+import re
+from typing import List, Tuple
+
+
+_HEADING_SANITIZE_RE = re.compile(r"[^a-z0-9]+")
+_HEADING_NUMBER_PREFIX_RE = re.compile(
+    r"^\s*(?P<number>(?:\d+|[ivxlcdm]+))(?P<suffix>(?:[\s.:;-].*)?)$",
+    re.IGNORECASE,
+)
+_ACRONYM_ALLOWLIST = {
+    "AI", "API", "CPU", "DIY", "GPU", "HTML", "HTTP", "HTTPS", "ID",
+    "JSON", "MP3", "MP4", "M4B", "NASA", "OCR", "PDF", "SQL", "TV",
+    "TTS", "UK", "UN", "UFO", "OK", "URL", "USA", "US", "VR",
+}
+_ROMAN_NUMERAL_CHARS = frozenset("IVXLCDM")
+_CAPS_WORD_RE = re.compile(r"[A-Z][A-Z0-9'\u2019-]*")
+
+
+def simplify_heading_text(text: str) -> str:
+    raw = str(text or "").strip().lower()
+    if not raw:
+        return ""
+    simplified = _HEADING_SANITIZE_RE.sub("", raw)
+    if simplified.startswith("chapter"):
+        simplified = simplified[7:]
+    return simplified
+
+
+def headings_equivalent(left: str, right: str) -> bool:
+    simple_left = simplify_heading_text(left)
+    simple_right = simplify_heading_text(right)
+    if not simple_left or not simple_right:
+        return False
+    if simple_left == simple_right:
+        return True
+    if simple_right.startswith(simple_left):
+        return True
+    if simple_left.startswith(simple_right):
+        return True
+    if len(simple_left) > 5 and simple_left in simple_right:
+        return True
+    return False
+
+
+def strip_duplicate_heading_line(text: str, heading: str) -> Tuple[str, bool]:
+    source_text = str(text or "")
+    if not source_text:
+        return source_text, False
+    normalized_heading = simplify_heading_text(heading)
+    if not normalized_heading:
+        return source_text, False
+    lines = source_text.splitlines()
+    new_lines: List[str] = []
+    removed = False
+    for line in lines:
+        stripped = line.strip()
+        if not removed and stripped:
+            if headings_equivalent(stripped, heading):
+                removed = True
+                continue
+        new_lines.append(line)
+    if not removed:
+        return source_text, False
+    while new_lines and not new_lines[0].strip():
+        new_lines.pop(0)
+    return "\n".join(new_lines), True
+
+
+def normalize_caps_word(word: str) -> str:
+    upper = word.upper()
+    letters = [char for char in upper if char.isalpha()]
+    if not letters:
+        return word
+    if upper in _ACRONYM_ALLOWLIST:
+        return word
+    if len(letters) <= 1:
+        return word
+    if all(char in _ROMAN_NUMERAL_CHARS for char in letters) and len(letters) <= 7:
+        return word
+
+    parts = re.split(r"(['\-\u2019])", word)
+    normalized_parts: List[str] = []
+    for part in parts:
+        if part in {"'", "-", "\u2019"}:
+            normalized_parts.append(part)
+            continue
+        if not part:
+            continue
+        normalized_parts.append(part[0].upper() + part[1:].lower())
+    return "".join(normalized_parts) or word
+
+
+def normalize_chapter_opening_caps(text: str) -> Tuple[str, bool]:
+    if not text:
+        return text, False
+
+    leading_len = len(text) - len(text.lstrip())
+    leading = text[:leading_len]
+    working = text[leading_len:]
+    if not working:
+        return text, False
+
+    builder: List[str] = []
+    pos = 0
+    changed = False
+
+    while pos < len(working):
+        char = working[pos]
+        if char in "\r\n":
+            builder.append(working[pos:])
+            pos = len(working)
+            break
+        if char.isspace():
+            builder.append(char)
+            pos += 1
+            continue
+        if char.islower():
+            builder.append(working[pos:])
+            pos = len(working)
+            break
+        if not char.isalpha():
+            builder.append(char)
+            pos += 1
+            continue
+
+        match = _CAPS_WORD_RE.match(working, pos)
+        if not match:
+            builder.append(char)
+            pos += 1
+            continue
+
+        word = match.group(0)
+        if any(ch.islower() for ch in word):
+            builder.append(working[pos:])
+            pos = len(working)
+            break
+
+        normalized = normalize_caps_word(word)
+        if normalized != word:
+            changed = True
+        builder.append(normalized)
+        pos = match.end()
+
+    if pos < len(working):
+        builder.append(working[pos:])
+
+    if not changed:
+        return text, False
+
+    return leading + "".join(builder), True
+
+
+def format_spoken_chapter_title(title: str, index: int, apply_prefix: bool) -> str:
+    base = str(title or "").strip()
+    if not base:
+        return f"Chapter {index}" if apply_prefix else ""
+    if not apply_prefix:
+        return base
+    lowered = base.lower()
+    if lowered.startswith("chapter") and (len(lowered) == 7 or not lowered[7].isalpha()):
+        return base
+    match = _HEADING_NUMBER_PREFIX_RE.match(base)
+    if match:
+        number = match.group("number") or ""
+        suffix = match.group("suffix") or ""
+        cleaned_suffix = suffix.lstrip(" .,:;-_ \t\u2013\u2014\u00b7\u2022")
+        if cleaned_suffix:
+            return f"Chapter {number}. {cleaned_suffix}"
+        return f"Chapter {number}"
+    return base
+
+
+def apply_chapter_text_transforms(
+    text: str,
+    *,
+    heading_text: str,
+    raw_title: str,
+    strip_heading: bool,
+    normalize_caps: bool,
+) -> Tuple[str, bool, bool]:
+    """Strip duplicate heading and normalize opening caps.
+
+    Returns ``(text, heading_removed, caps_changed)``.
+    The caller is responsible for state updates (pending flags, logging,
+    dict mutation, ``continue``).
+    """
+    heading_removed = False
+    caps_changed = False
+
+    if strip_heading and heading_text:
+        text, heading_removed = strip_duplicate_heading_line(text, heading_text)
+        if not heading_removed and raw_title:
+            match = _HEADING_NUMBER_PREFIX_RE.match(raw_title)
+            if match:
+                number = match.group("number")
+                if number:
+                    text, heading_removed = strip_duplicate_heading_line(text, number)
+
+    if normalize_caps and text:
+        text, caps_changed = normalize_chapter_opening_caps(text)
+
+    return text, heading_removed, caps_changed

abogen/domain/chunk_utils.py

@@ -0,0 +1,76 @@
+"""Chunk processing utilities.
+
+Functions for grouping chunks, recording override usage, and selecting
+text for TTS synthesis.
+"""
+
+from __future__ import annotations
+
+from collections import defaultdict
+from typing import Any, Dict, Iterable, Mapping
+
+from abogen.domain.enums import Language
+from abogen.pronunciation_store import increment_usage
+
+
+def safe_int(value: Any, default: int = 0) -> int:
+    try:
+        return int(value)
+    except (TypeError, ValueError):
+        return default
+
+
+def group_chunks_by_chapter(chunks: Iterable[Dict[str, Any]]) -> Dict[int, List[Dict[str, Any]]]:
+    grouped: Dict[int, List[Dict[str, Any]]] = defaultdict(list)
+    for entry in chunks or []:
+        if not isinstance(entry, dict):
+            continue
+        try:
+            chapter_index = int(entry.get("chapter_index", 0))
+        except (TypeError, ValueError):
+            chapter_index = 0
+        grouped[chapter_index].append(dict(entry))
+
+    for chapter_index, items in grouped.items():
+        items.sort(key=lambda payload: safe_int(payload.get("chunk_index")))
+
+    return grouped
+
+
+def record_override_usage(
+    job: Any,
+    usage_counter: Mapping[str, int],
+    token_map: Mapping[str, str],
+) -> None:
+    if not usage_counter:
+        return
+
+    language = getattr(job, "language", Language.EN_US) or Language.EN_US
+    for normalized, amount in usage_counter.items():
+        if amount <= 0:
+            continue
+        token_value = token_map.get(normalized, normalized)
+        try:
+            increment_usage(language=language, token=token_value, amount=int(amount))
+        except Exception:  # pragma: no cover - defensive logging
+            job.add_log(f"Failed to record usage for override {token_value}", level="warning")
+
+
+def chunk_text_for_tts(entry: Mapping[str, Any]) -> str:
+    """Choose the best source text for synthesis.
+
+    We must prefer the raw chunk text (``text`` / ``original_text``) so
+    manual/pronunciation overrides can match against the original tokens
+    (e.g. censored words like ``Unfu*k``).  ``normalized_text`` may have
+    already been run through ``normalize_for_pipeline``, which can remove
+    punctuation and prevent overrides from triggering.
+    """
+
+    if not isinstance(entry, Mapping):
+        return ""
+    return str(
+        entry.get("text")
+        or entry.get("original_text")
+        or entry.get("normalized_text")
+        or ""
+    ).strip()

abogen/domain/config_types.py

@@ -0,0 +1,52 @@
+"""Domain config types — shared contracts for domain functions.
+
+These dataclasses group parameters that domain functions receive.
+Domain defines them, app layer fills them.
+
+Why here (domain) and not application:
+- build_tts_context() is in domain → needs PronunciationConfig
+- make_subtitle_writer() is in infrastructure → needs SubtitleConfig
+- embed_m4b_metadata() is in infrastructure → needs CoverConfig
+- Domain should not depend on application layer (DIP)
+"""
+
+from __future__ import annotations
+
+from dataclasses import dataclass, field
+from pathlib import Path
+from typing import Any, Dict, List, Optional
+
+from abogen.domain.enums import SubtitleFormat, SubtitleMode
+
+
+@dataclass(frozen=True)
+class PronunciationConfig:
+    """Pronunciation and normalization override settings.
+
+    Used by build_tts_context() to compile override rules.
+    """
+    pronunciation_overrides: List[Dict[str, Any]] = field(default_factory=list)
+    manual_overrides: List[Dict[str, Any]] = field(default_factory=list)
+    heteronym_overrides: List[Dict[str, Any]] = field(default_factory=list)
+    normalization_overrides: Optional[Dict[str, Any]] = None
+
+
+@dataclass(frozen=True)
+class SubtitleConfig:
+    """Subtitle output settings.
+
+    Used by make_subtitle_writer() and process_and_write_subtitles().
+    """
+    mode: SubtitleMode = SubtitleMode.DISABLED
+    format: SubtitleFormat = SubtitleFormat.SRT
+    max_words: int = 50
+
+
+@dataclass(frozen=True)
+class CoverConfig:
+    """Cover image settings.
+
+    Used by embed_m4b_metadata() and build_epub3_package().
+    """
+    path: Optional[Path] = None
+    mime: Optional[str] = None

abogen/domain/conversion_engine.py

@@ -0,0 +1,241 @@
+"""Shared TTS iteration loop used by both WebUI and PyQt conversion runners.
+
+The core pattern is identical across both UIs:
+
+    for seg in tts_segments(text, backend, voice, speed, split_pattern, current_time):
+        check_cancel()
+        update_progress(seg)
+        write_audio(seg, sink)
+        accumulate_subtitles(seg)
+
+After the loop, the caller processes accumulated subtitle tokens.
+
+This module provides ``run_tts_segment_loop`` which encapsulates that
+iteration, and ``synthesize_text`` which adds normalization on top —
+the single entry point both UIs should call for text-to-speech.
+"""
+
+from __future__ import annotations
+
+import time
+from dataclasses import dataclass, field
+from typing import Any, Callable, Optional, Protocol
+
+from abogen.domain.audio_sink import AudioSink
+from abogen.domain.conversion_pipeline import tts_segments
+from abogen.domain.enums import Language, SubtitleMode
+from abogen.domain.normalization import TTSContext
+from abogen.domain.progress import calc_etr_str
+from abogen.domain.subtitle_generation import process_subtitle_tokens
+
+
+class CancelChecker(Protocol):
+    """Returns True if conversion has been cancelled."""
+    def __call__(self) -> bool: ...
+
+
+@dataclass
+class SegmentStats:
+    """Running statistics updated per TTS segment."""
+    processed_chars: int = 0
+    current_time: float = 0.0
+    etr_start_time: float = field(default_factory=time.time)
+    total_characters: int = 0
+
+
+@dataclass
+class SegmentInfo:
+    """Read-only info about a TTS segment, passed to on_segment callback."""
+    graphemes: str
+    audio: Any
+    tokens: list
+    duration: float
+    chunk_start: float
+
+
+def run_tts_segment_loop(
+    *,
+    text: str,
+    params: SynthParams,
+    backend: Any,
+    voice: Any,
+    speed: float,
+    split_pattern: str,
+    total_steps: Optional[int] = None,
+    chapter_sink: Optional[AudioSink] = None,
+    preview_callback: Optional[Callable[[str], None]] = None,
+    on_segment: Optional[Callable[[SegmentInfo], None]] = None,
+) -> tuple[int, list]:
+    """Run the core TTS segment iteration loop.
+
+    Args:
+        text: Normalized text to synthesize.
+        params: Common synthesis parameters (stats, callbacks, sinks, etc.).
+        backend: TTS pipeline instance (Kokoro or Supertonic).
+        voice: Voice name/id for the backend.
+        speed: Speech speed multiplier.
+        split_pattern: Regex pattern used by the TTS engine for sentence splitting.
+        total_steps: Inference quality steps (Supertonic only, ignored by Kokoro).
+        preview_callback: Called with a short preview string per segment.
+        on_segment: Called with a SegmentInfo for each segment *before*
+            audio is written.  Useful for callers that need per-segment
+            subtitle processing (e.g. PyQt dual-writer pattern).
+            When provided, the default subtitle accumulation is skipped.
+
+    Returns:
+        Tuple of (segment_count, accumulated_subtitle_tokens).
+        The caller is responsible for processing subtitle tokens via
+        ``process_subtitle_tokens`` and writing entries to subtitle writers.
+    """
+    local_segments = 0
+    accumulated_tokens: list[dict] = []
+
+    for seg in tts_segments(
+        text,
+        backend=backend,
+        voice=voice,
+        speed=speed,
+        split_pattern=split_pattern,
+        current_time=params.stats.current_time,
+        total_steps=total_steps,
+    ):
+        if params.check_cancel():
+            break
+
+        local_segments += 1
+        params.stats.processed_chars += len(seg.graphemes)
+
+        # Progress
+        if params.stats.total_characters:
+            percent = min(int(params.stats.processed_chars / params.stats.total_characters * 100), 99)
+        else:
+            percent = 0 if params.stats.processed_chars == 0 else 99
+
+        etr_str = calc_etr_str(
+            time.time() - params.stats.etr_start_time,
+            params.stats.processed_chars,
+            params.stats.total_characters,
+        )
+        params.on_progress(percent, etr_str)
+
+        # Preview / log
+        if preview_callback:
+            preview_callback(seg.graphemes or "[silence]")
+
+        # Per-segment callback (for callers needing segment-level access)
+        if on_segment:
+            info = SegmentInfo(
+                graphemes=seg.graphemes,
+                audio=seg.audio,
+                tokens=list(seg.tokens) if seg.tokens else [],
+                duration=seg.duration,
+                chunk_start=getattr(seg, "chunk_start", params.stats.current_time),
+            )
+            on_segment(info)
+
+        # Write audio
+        if chapter_sink:
+            chapter_sink.write(seg.audio)
+        if params.audio_sink:
+            params.audio_sink.write(seg.audio)
+
+        # Accumulate subtitle tokens (default path; skipped if on_segment handles it)
+        if not on_segment and params.subtitle_mode != SubtitleMode.DISABLED and seg.tokens:
+            accumulated_tokens.extend(seg.tokens)
+
+        # Update timing
+        if params.audio_sink:
+            params.stats.current_time += seg.duration
+
+    return local_segments, accumulated_tokens
+
+
+def process_and_write_subtitles(
+    accumulated_tokens: list[dict],
+    subtitle_writer: Any,
+    *,
+    subtitle: "SubtitleConfig | str",
+    max_subtitle_words: int | None = None,
+    language: Language,
+    use_spacy_segmentation: bool,
+    fallback_end_time: float,
+) -> None:
+    """Process accumulated subtitle tokens and write entries to a subtitle writer.
+
+    Accepts a SubtitleConfig object or a subtitle mode string
+    for backward compatibility.
+    """
+    from abogen.domain.config_types import SubtitleConfig
+
+    if isinstance(subtitle, SubtitleConfig):
+        mode_str = subtitle.mode.value
+        words = subtitle.max_words
+    else:
+        mode_str = subtitle
+        words = max_subtitle_words or 50
+
+    if not accumulated_tokens or not subtitle_writer:
+        return
+    new_entries: list[tuple] = []
+    process_subtitle_tokens(
+        accumulated_tokens,
+        new_entries,
+        words,
+        mode_str,
+        language,
+        use_spacy_segmentation=use_spacy_segmentation,
+        fallback_end_time=fallback_end_time,
+    )
+    for start, end, text in new_entries:
+        subtitle_writer.write_entry(start=start, end=end, text=text)
+
+
+@dataclass(frozen=True)
+class SynthParams:
+    """Common parameters for synthesize_text calls.
+
+    Packed once by the executor to avoid repeating identical kwargs.
+    When adding new common params, change only this dataclass.
+    """
+    tts_context: TTSContext
+    stats: SegmentStats
+    check_cancel: CancelChecker
+    on_progress: Callable[[int, str], None]
+    audio_sink: Optional[AudioSink] = None
+    subtitle_mode: str = "Disabled"
+    max_subtitle_words: int = 50
+    language: Language = Language.EN_US
+    use_spacy_segmentation: bool = False
+
+
+def synthesize_text(
+    *,
+    text: str,
+    params: SynthParams,
+    backend: Any,
+    voice: Any,
+    speed: float,
+    total_steps: Optional[int] = None,
+    chapter_sink: Optional[AudioSink] = None,
+    preview_callback: Optional[Callable[[str], None]] = None,
+    on_segment: Optional[Callable[[SegmentInfo], None]] = None,
+    split_pattern_override: Optional[str] = None,
+) -> tuple[int, list]:
+    """Normalize text and run TTS — the single entry point for both UIs.
+
+    Combines TTSContext.normalize() + run_tts_segment_loop() into one call.
+    UI-specific concerns (provider resolution, progress display) stay in the UI.
+    """
+    normalized = params.tts_context.normalize(text)
+    return run_tts_segment_loop(
+        text=normalized,
+        params=params,
+        backend=backend,
+        voice=voice,
+        speed=speed,
+        total_steps=total_steps,
+        split_pattern=split_pattern_override or params.tts_context.split_pattern,
+        chapter_sink=chapter_sink,
+        preview_callback=preview_callback,
+        on_segment=on_segment,
+    )

abogen/domain/conversion_pipeline.py

@@ -0,0 +1,357 @@
+"""Shared TTS emission pipeline.
+
+Provides the core TTS emission loop used by both WebUI and PyQt conversion runners.
+The caller handles audio I/O, progress reporting, and subtitle writing.
+"""
+
+from __future__ import annotations
+
+import logging
+from dataclasses import dataclass, field
+
+from abogen.domain.enums import Language, SubtitleMode
+from typing import Any, Callable, Dict, Iterator, List, Optional, Tuple
+
+import numpy as np
+
+from abogen.domain.audio_helpers import to_float32
+from abogen.domain.normalization import prepare_text_for_tts
+from abogen.domain.tokens import FakeToken
+from abogen.domain.audio_buffer import SAMPLE_RATE
+
+logger = logging.getLogger(__name__)
+
+# Languages where spaCy is used for pre-TTS segmentation
+# English ("a", "b") is excluded — spaCy only used for post-TTS subtitles
+_SPACY_EXCLUDED_LANGS = {Language.EN_US, Language.EN_GB}
+
+# CJK languages — different spacing pattern
+_CJK_LANGS = {Language.ZH, Language.JA}
+
+
+def spacy_pre_tts_segmentation(
+    text: str,
+    lang_code: Any,
+    subtitle_mode: Any,
+    *,
+    is_subtitle_input: bool = False,
+    use_spacy_segmentation: bool = True,
+    log_callback: Optional[Callable[[str], None]] = None,
+) -> Tuple[List[str], str]:
+    """Segment text using spaCy before TTS, with split_pattern override.
+
+    For non-English languages, spaCy sentence segmentation produces better
+    sentence boundaries than regex. This function:
+    1. Checks if spaCy should be used (toggle on, not disabled mode, not subtitle input)
+    2. For non-English: runs spaCy segmentation, computes split_pattern override
+    3. For English: returns single segment with default pattern (spaCy only for subtitles)
+    4. If spaCy fails: falls back to default pattern
+
+    Args:
+        text: Text to segment.
+        lang_code: Language code (Language enum or string like "a", "de", "fr").
+        subtitle_mode: SubtitleMode enum or string.
+        is_subtitle_input: True if source is .srt/.ass/.vtt file.
+        use_spacy_segmentation: User toggle for spaCy segmentation.
+        log_callback: Optional logging function.
+
+    Returns:
+        Tuple of (text_segments, active_split_pattern).
+        text_segments is a list of sentences (always at least one element).
+        active_split_pattern is the regex to use for TTS backend splitting.
+    """
+    from abogen.domain.split_pattern import PUNCTUATION_COMMAS, get_split_pattern
+
+    def _log(msg: str) -> None:
+        if log_callback:
+            log_callback(msg)
+
+    # Normalize language
+    lang_enum = _to_language_enum(lang_code)
+
+    # Default split pattern
+    default_split = get_split_pattern(lang_code, subtitle_mode)
+
+    # Check conditions
+    if not use_spacy_segmentation:
+        return [text], default_split
+
+    subtitle_mode_str = _to_subtitle_mode_str(subtitle_mode)
+    if subtitle_mode_str in ("Disabled", "Line"):
+        return [text], default_split
+
+    if is_subtitle_input:
+        return [text], default_split
+
+    # English: spaCy only for post-TTS subtitles, not pre-TTS
+    if lang_enum in _SPACY_EXCLUDED_LANGS:
+        return [text], default_split
+
+    # Non-English: run spaCy pre-TTS segmentation
+    from abogen.spacy_utils import segment_sentences
+
+    _log("Using spaCy for sentence segmentation (pre-TTS)...")
+    spacy_sentences = segment_sentences(text, lang_code, log_callback=log_callback)
+
+    if not spacy_sentences:
+        _log("spaCy: Fallback to default segmentation...")
+        return [text], default_split
+
+    _log(f"spaCy: Text segmented into {len(spacy_sentences)} sentences...")
+
+    # Compute split_pattern override based on subtitle mode
+    spacing_pattern = r"\s*" if lang_enum in _CJK_LANGS else r"\s+"
+
+    if subtitle_mode_str == "Sentence + Comma":
+        active_split = r"(?<=[{}]){}|\n+".format(PUNCTUATION_COMMAS, spacing_pattern)
+    else:
+        # Sentence mode: spaCy already split, only split on newlines
+        active_split = "\n"
+
+    return spacy_sentences, active_split
+
+
+def _to_language_enum(lang_code: Any) -> Language:
+    """Convert lang_code to Language enum."""
+    if isinstance(lang_code, Language):
+        return lang_code
+    try:
+        return Language.from_str(str(lang_code))
+    except (ValueError, AttributeError):
+        return Language.EN_US
+
+
+def _to_subtitle_mode_str(subtitle_mode: Any) -> str:
+    """Convert subtitle_mode to string."""
+    if isinstance(subtitle_mode, SubtitleMode):
+        return subtitle_mode.value
+    return str(subtitle_mode)
+
+
+@dataclass
+class SegmentResult:
+    """One TTS segment emitted by the pipeline."""
+    graphemes: str
+    audio: np.ndarray
+    duration: float
+    chunk_start: float
+    tokens: List[Dict[str, Any]] = field(default_factory=list)
+
+
+def tts_segments(
+    text: str,
+    *,
+    backend: Any,
+    voice: Any,
+    speed: float,
+    split_pattern: str,
+    current_time: float = 0.0,
+    total_steps: Optional[int] = None,
+) -> Iterator[SegmentResult]:
+    """Invoke TTS backend on (already normalized) text and yield SegmentResults.
+
+    Use this when you've already normalized the text yourself (e.g. after
+    spaCy sentence segmentation). For raw text, use emit_text_segments() instead.
+
+    Args:
+        text: Already-normalized text to synthesize.
+        backend: TTS pipeline callable.
+        voice: Resolved voice.
+        speed: TTS speed multiplier.
+        split_pattern: Regex pattern for sentence splitting.
+        current_time: Current position in the audio timeline (seconds).
+        total_steps: Inference quality steps (Supertonic only, ignored by Kokoro).
+
+    Yields:
+        SegmentResult for each non-empty TTS segment.
+    """
+    kwargs: dict[str, Any] = dict(
+        voice=voice,
+        speed=speed,
+        split_pattern=split_pattern,
+    )
+    if total_steps is not None:
+        kwargs["total_steps"] = total_steps
+
+    segment_iter = backend(text, **kwargs)
+
+    chunk_start = current_time
+
+    for segment in segment_iter:
+        graphemes_raw = getattr(segment, "graphemes", "") or ""
+        graphemes = graphemes_raw.strip()
+
+        audio = to_float32(getattr(segment, "audio", None))
+        if audio.size == 0:
+            continue
+
+        duration = len(audio) / SAMPLE_RATE
+
+        tokens_list = getattr(segment, "tokens", [])
+        if not tokens_list and graphemes:
+            tokens_list = [FakeToken(graphemes, 0, duration)]
+
+        tokens = [
+            {
+                "start": chunk_start + (tok.start_ts or 0),
+                "end": chunk_start + (tok.end_ts or 0),
+                "text": tok.text,
+                "whitespace": tok.whitespace,
+            }
+            for tok in tokens_list
+        ]
+
+        yield SegmentResult(
+            graphemes=graphemes,
+            audio=audio,
+            duration=duration,
+            chunk_start=chunk_start,
+            tokens=tokens,
+        )
+
+        chunk_start += duration
+
+
+def emit_text_segments(
+    text: str,
+    *,
+    backend: Any,
+    voice: Any,
+    speed: float,
+    split_pattern: str,
+    current_time: float = 0.0,
+    total_steps: Optional[int] = None,
+    # normalization
+    heteronym_rules: Any = None,
+    pronunciation_rules: Any = None,
+    normalization_overrides: Any = None,
+    usage_counter: Optional[Dict[str, int]] = None,
+) -> Iterator[SegmentResult]:
+    """Normalize text and yield SegmentResults from the TTS backend.
+
+    This is the innermost TTS emission loop shared by both UIs. It handles:
+    1. Text normalization (heteronym + pronunciation rules)
+    2. TTS backend invocation
+    3. Segment iteration with token extraction
+
+    The caller is responsible for:
+    - Writing audio to sinks
+    - Accumulating tokens for subtitle processing
+    - Progress tracking and cancellation
+    - Error handling
+
+    Args:
+        text: Raw text to synthesize.
+        backend: TTS pipeline callable (kokoro or supertonic).
+        voice: Resolved voice for TTS.
+        speed: TTS speed multiplier.
+        split_pattern: Regex pattern for sentence splitting.
+        current_time: Current position in the audio timeline (seconds).
+        heteronym_rules: Compiled heteronym rules.
+        pronunciation_rules: Compiled pronunciation rules.
+        normalization_overrides: User normalization overrides.
+        usage_counter: Counter for normalization statistics.
+
+    Yields:
+        SegmentResult for each non-empty TTS segment.
+    """
+    source_text = str(text or "")
+    normalized = prepare_text_for_tts(
+        source_text,
+        heteronym_rules=heteronym_rules,
+        pronunciation_rules=pronunciation_rules,
+        normalization_overrides=normalization_overrides,
+        usage_counter=usage_counter,
+    )
+
+    yield from tts_segments(
+        normalized,
+        backend=backend,
+        voice=voice,
+        speed=speed,
+        split_pattern=split_pattern,
+        current_time=current_time,
+        total_steps=total_steps,
+    )
+
+
+def emit_text_to_sinks(
+    text: str,
+    *,
+    backend: Any,
+    voice: Any,
+    speed: float,
+    split_pattern: str,
+    current_time: float = 0.0,
+    # sinks
+    audio_sink: Any = None,
+    chapter_sink: Any = None,
+    # subtitle
+    subtitle_writer: Any = None,
+    subtitle_mode: str = "Disabled",
+    subtitle_lang: Language = Language.EN_US,
+    max_subtitle_words: int = 50,
+    use_spacy_segmentation: bool = True,
+    # normalization
+    heteronym_rules: Any = None,
+    pronunciation_rules: Any = None,
+    normalization_overrides: Any = None,
+    usage_counter: Optional[Dict[str, int]] = None,
+) -> tuple[int, float, List[Dict[str, Any]]]:
+    """Emit TTS audio for text, writing to sinks and collecting subtitle tokens.
+
+    Convenience wrapper around emit_text_segments() that handles audio writing
+    and token accumulation. Returns stats for the caller to update progress.
+
+    Returns:
+        Tuple of (segments_emitted, new_current_time, accumulated_tokens).
+    """
+    from abogen.domain.subtitle_generation import process_subtitle_tokens
+
+    segments_emitted = 0
+    accumulated_tokens: List[Dict[str, Any]] = []
+
+    for seg in emit_text_segments(
+        text,
+        backend=backend,
+        voice=voice,
+        speed=speed,
+        split_pattern=split_pattern,
+        current_time=current_time,
+        heteronym_rules=heteronym_rules,
+        pronunciation_rules=pronunciation_rules,
+        normalization_overrides=normalization_overrides,
+        usage_counter=usage_counter,
+    ):
+        segments_emitted += 1
+
+        # Write audio
+        if chapter_sink:
+            chapter_sink.write(seg.audio)
+        if audio_sink:
+            audio_sink.write(seg.audio)
+
+        # Collect tokens
+        accumulated_tokens.extend(seg.tokens)
+
+    # Flush subtitle tokens
+    if subtitle_writer and accumulated_tokens:
+        _use_spacy = subtitle_mode not in (SubtitleMode.DISABLED, SubtitleMode.LINE)
+        new_entries: List[tuple] = []
+        process_subtitle_tokens(
+            accumulated_tokens,
+            new_entries,
+            max_subtitle_words,
+            subtitle_mode,
+            subtitle_lang,
+            use_spacy_segmentation=_use_spacy,
+            fallback_end_time=current_time + sum(t["end"] - t["start"] for t in accumulated_tokens if accumulated_tokens),
+        )
+        for start, end, text_entry in new_entries:
+            subtitle_writer.write_entry(start=start, end=end, text=text_entry)
+
+    new_time = current_time
+    if accumulated_tokens:
+        new_time = max(t["end"] for t in accumulated_tokens)
+
+    return segments_emitted, new_time, accumulated_tokens

abogen/domain/device.py

@@ -0,0 +1,31 @@
+from __future__ import annotations
+
+import platform as _platform
+
+
+def select_device() -> str:
+    """Return the best available compute device (``"mps"``, ``"cuda"``, or ``"cpu"``).
+
+    Checks ``torch`` availability at runtime so this can be called from
+    any context without requiring torch at import time.
+    """
+    try:
+        import torch  # type: ignore[import-not-found]
+    except Exception:
+        return "cpu"
+
+    system = _platform.system()
+    if system == "Darwin" and _platform.processor() == "arm":
+        try:
+            if torch.backends.mps.is_available():  # type: ignore[union-attr]
+                return "mps"
+        except Exception:
+            pass
+        return "cpu"
+
+    try:
+        if torch.cuda.is_available():  # type: ignore[union-attr]
+            return "cuda"
+    except Exception:
+        pass
+    return "cpu"

abogen/domain/enums.py

@@ -0,0 +1,227 @@
+"""Domain enums — typed constants for values tied to business logic.
+
+Using Enum instead of bare strings ensures:
+- Invalid values are caught at construction time
+- IDE autocomplete and type checking work
+- Adding new values is explicit (must update Enum)
+"""
+
+from __future__ import annotations
+
+from enum import Enum
+from pathlib import Path
+
+
+class SubtitleMode(str, Enum):
+    """Subtitle generation mode."""
+    DISABLED = "Disabled"
+    LINE = "Line"
+    SENTENCE = "Sentence"
+    SENTENCE_COMMA = "Sentence + Comma"
+    SENTENCE_HIGHLIGHT = "Sentence + Highlighting"
+
+    @classmethod
+    def from_str(cls, value: str) -> SubtitleMode:
+        """Parse from user input: case-insensitive, strips whitespace."""
+        normalized = value.strip()
+        for member in cls:
+            if member.value.lower() == normalized.lower():
+                return member
+        raise ValueError(f"Invalid SubtitleMode: {value!r}. Valid: {[m.value for m in cls]}")
+
+
+class OutputFormat(str, Enum):
+    """Audio output format."""
+    WAV = "wav"
+    MP3 = "mp3"
+    FLAC = "flac"
+    OPUS = "opus"
+    M4B = "m4b"
+
+    @property
+    def dot_ext(self) -> str:
+        """File extension with dot: '.wav', '.mp3', etc."""
+        return f".{self.value}"
+
+    @property
+    def is_lossless(self) -> bool:
+        """True for lossless formats."""
+        return self in (self.WAV, self.FLAC)
+
+    @classmethod
+    def from_str(cls, value: str) -> OutputFormat:
+        """Parse from user input: strips dot prefix, case-insensitive."""
+        normalized = value.strip().lstrip(".").lower()
+        for member in cls:
+            if member.value == normalized:
+                return member
+        raise ValueError(f"Invalid OutputFormat: {value!r}. Valid: {[m.value for m in cls]}")
+
+
+class SaveMode(str, Enum):
+    """Where to save the output file."""
+    SAVE_NEXT_TO_INPUT = "save_next_to_input"
+    SAVE_TO_DESKTOP = "save_to_desktop"
+    CHOOSE_OUTPUT_FOLDER = "choose_output_folder"
+    DEFAULT_OUTPUT = "default_output"
+    CUSTOM_FOLDER = "custom_folder"
+
+
+class SubtitleFormat(str, Enum):
+    """Subtitle file format."""
+    SRT = "srt"
+    ASS = "ass"
+    VTT = "vtt"
+
+    @property
+    def dot_ext(self) -> str:
+        """File extension with dot: '.srt', '.ass'."""
+        return f".{self.value}"
+
+    @classmethod
+    def from_str(cls, value: str) -> SubtitleFormat:
+        """Parse from user input: strips dot prefix, case-insensitive."""
+        normalized = value.strip().lstrip(".").lower()
+        for member in cls:
+            if member.value == normalized:
+                return member
+        raise ValueError(f"Invalid SubtitleFormat: {value!r}. Valid: {[m.value for m in cls]}")
+
+
+class InputFormat(str, Enum):
+    """Input file format."""
+    EPUB = "epub"
+    PDF = "pdf"
+    TXT = "txt"
+    MD = "md"
+    SRT = "srt"
+    ASS = "ass"
+    VTT = "vtt"
+
+    @property
+    def is_book(self) -> bool:
+        """True for book/document formats (epub, pdf, txt, md)."""
+        return self in (self.EPUB, self.PDF, self.TXT, self.MD)
+
+    @property
+    def is_subtitle(self) -> bool:
+        """True for subtitle formats (srt, ass, vtt)."""
+        return self in (self.SRT, self.ASS, self.VTT)
+
+    @property
+    def dot_ext(self) -> str:
+        """File extension with dot: '.epub', '.srt', etc."""
+        return f".{self.value}"
+
+    @classmethod
+    def from_path(cls, path: Path) -> InputFormat:
+        """Detect format from file path extension."""
+        suffix = path.suffix.lower().lstrip(".")
+        if suffix == "markdown":
+            return cls.MD
+        try:
+            return cls(suffix)
+        except ValueError:
+            raise ValueError(f"Unsupported input format: {path.suffix!r}. Supported: {[m.value for m in cls]}")
+
+
+class Language(str, Enum):
+    """TTS language code (ISO 639-1 with region where needed).
+
+    Each engine maps these to its own internal language identifiers.
+    Engines report which languages they support via ``supported_languages()``.
+    """
+    EN_US = "en-US"
+    EN_GB = "en-GB"
+    ES = "es"
+    FR = "fr"
+    HI = "hi"
+    IT = "it"
+    JA = "ja"
+    PT_BR = "pt-BR"
+    ZH = "zh"
+    AR = "ar"
+    BG = "bg"
+    CS = "cs"
+    DA = "da"
+    DE = "de"
+    EL = "el"
+    ET = "et"
+    FI = "fi"
+    HR = "hr"
+    HU = "hu"
+    ID = "id"
+    KO = "ko"
+    LT = "lt"
+    LV = "lv"
+    NL = "nl"
+    PL = "pl"
+    RO = "ro"
+    RU = "ru"
+    SK = "sk"
+    SL = "sl"
+    SV = "sv"
+    TR = "tr"
+    UK = "uk"
+    VI = "vi"
+
+    @property
+    def display_name(self) -> str:
+        """Human-readable language name."""
+        _names = {
+            "en-US": "American English",
+            "en-GB": "British English",
+            "es": "Spanish",
+            "fr": "French",
+            "hi": "Hindi",
+            "it": "Italian",
+            "ja": "Japanese",
+            "pt-BR": "Brazilian Portuguese",
+            "zh": "Mandarin Chinese",
+            "ar": "Arabic",
+            "bg": "Bulgarian",
+            "cs": "Czech",
+            "da": "Danish",
+            "de": "German",
+            "el": "Greek",
+            "et": "Estonian",
+            "fi": "Finnish",
+            "hr": "Croatian",
+            "hu": "Hungarian",
+            "id": "Indonesian",
+            "ko": "Korean",
+            "lt": "Lithuanian",
+            "lv": "Latvian",
+            "nl": "Dutch",
+            "pl": "Polish",
+            "ro": "Romanian",
+            "ru": "Russian",
+            "sk": "Slovak",
+            "sl": "Slovenian",
+            "sv": "Swedish",
+            "tr": "Turkish",
+            "uk": "Ukrainian",
+            "vi": "Vietnamese",
+        }
+        return _names[self.value]
+
+    @property
+    def is_cjk(self) -> bool:
+        """True for CJK languages (Chinese, Japanese, Korean)."""
+        return self in (self.ZH, self.JA, self.KO)
+
+    @property
+    def supports_subtitle_tokens(self) -> bool:
+        """True if this language generates timestamped tokens for subtitles."""
+        return self in (self.EN_US, self.EN_GB)
+
+    @classmethod
+    def from_str(cls, value: str) -> Language:
+        """Parse from user input: ISO code, case-insensitive."""
+        if isinstance(value, Language):
+            return value
+        normalized = value.strip()
+        for member in cls:
+            if member.value.lower() == normalized.lower():
+                return member
+        raise ValueError(f"Invalid Language: {value!r}. Valid: {[m.value for m in cls]}")

abogen/domain/file_type.py

@@ -0,0 +1,136 @@
+from __future__ import annotations
+
+import re
+from dataclasses import dataclass
+from pathlib import Path
+from typing import Any, Dict, List, Tuple
+
+from abogen.text_extractor import ExtractedChapter
+
+
+_SIGNIFICANT_LENGTH_THRESHOLDS: Dict[str, int] = {"epub": 1000, "markdown": 500}
+_MIN_SHORT_CONTENT: Dict[str, int] = {"epub": 240, "markdown": 160}
+_STRUCTURAL_KEYWORDS = (
+    "preface",
+    "prologue",
+    "introduction",
+    "foreword",
+    "epilogue",
+    "afterword",
+    "appendix",
+    "acknowledgment",
+    "acknowledgement",
+)
+_STRUCTURAL_MIN_LENGTH = 120
+_MAX_SHORT_CHAPTERS = 2
+
+
+@dataclass
+class ChapterFilterResult:
+    kept: List[ExtractedChapter]
+    skipped: List[Tuple[str, int]]
+
+
+def infer_file_type(path: Path) -> str:
+    suffix = path.suffix.lower()
+    if suffix == ".epub":
+        return "epub"
+    if suffix in {".md", ".markdown"}:
+        return "markdown"
+    if suffix == ".pdf":
+        return "pdf"
+    if suffix == ".txt":
+        return "text"
+    return suffix.lstrip(".") or "text"
+
+
+def looks_structural(title: str) -> bool:
+    lowered = title.strip().lower()
+    if not lowered:
+        return False
+    return any(keyword in lowered for keyword in _STRUCTURAL_KEYWORDS)
+
+
+def chapter_label(file_type: str) -> str:
+    return "chapters" if file_type.lower() in {"epub", "markdown"} else "pages"
+
+
+def auto_select_relevant_chapters(
+    chapters: List[ExtractedChapter],
+    file_type: str,
+) -> ChapterFilterResult:
+    if not chapters:
+        return ChapterFilterResult(kept=[], skipped=[])
+
+    normalized = file_type.lower()
+    threshold = _SIGNIFICANT_LENGTH_THRESHOLDS.get(normalized, 0)
+    min_short = _MIN_SHORT_CONTENT.get(normalized, 0)
+
+    kept: List[ExtractedChapter] = []
+    skipped: List[Tuple[str, int]] = []
+    short_kept = 0
+
+    for chapter in chapters:
+        stripped = chapter.text.strip()
+        length = len(stripped)
+        if length == 0:
+            skipped.append((chapter.title, length))
+            continue
+
+        keep = False
+        if threshold == 0:
+            keep = True
+        elif length >= threshold:
+            keep = True
+        elif not kept:
+            keep = True
+        elif min_short and length >= min_short and short_kept < _MAX_SHORT_CHAPTERS:
+            keep = True
+            short_kept += 1
+        elif looks_structural(chapter.title) and length >= _STRUCTURAL_MIN_LENGTH:
+            keep = True
+
+        if keep:
+            kept.append(chapter)
+        else:
+            skipped.append((chapter.title, length))
+
+    if kept:
+        return ChapterFilterResult(kept=kept, skipped=skipped)
+
+    longest_idx = None
+    longest_length = 0
+    for idx, chapter in enumerate(chapters):
+        stripped = chapter.text.strip()
+        if stripped and len(stripped) > longest_length:
+            longest_length = len(stripped)
+            longest_idx = idx
+
+    if longest_idx is not None:
+        longest = chapters[longest_idx]
+        fallback_skipped = [
+            (chapter.title, len(chapter.text.strip()))
+            for idx, chapter in enumerate(chapters)
+            if idx != longest_idx and chapter.text.strip()
+        ]
+        return ChapterFilterResult(kept=[longest], skipped=fallback_skipped)
+
+    return ChapterFilterResult(kept=[], skipped=skipped)
+
+
+def update_metadata_for_chapter_count(
+    metadata: Dict[str, Any], count: int, file_type: str
+) -> None:
+    if not metadata or count <= 0:
+        return
+
+    label = "Chapters" if file_type.lower() in {"epub", "markdown"} else "Pages"
+    metadata["chapter_count"] = str(count)
+
+    pattern = re.compile(r"\(\d+\s+(Chapters?|Pages?)\)")
+    replacement = f"({count} {label})"
+    for key in ("album", "ALBUM"):
+        value = metadata.get(key)
+        if not isinstance(value, str):
+            continue
+        metadata[key] = pattern.sub(replacement, value)

abogen/domain/intro_outro.py

@@ -0,0 +1,83 @@
+"""Intro/outro text building and voice resolution for audiobook conversion.
+
+Both UIs (WebUI and Desktop) need to:
+1. Build intro/outro text from book metadata
+2. Resolve which voice to use for intro/outro synthesis
+
+This module provides the shared domain logic. The actual TTS synthesis
+and audio writing remain UI-specific.
+"""
+
+from __future__ import annotations
+
+from dataclasses import dataclass
+from typing import Any, Dict, Optional
+
+from abogen.domain.title_builder import build_title_intro_text, build_outro_text
+from abogen.domain.voice_resolution import resolve_fallback_voice_spec
+
+
+@dataclass
+class IntroOutroSpec:
+    """Resolved intro or outro specification ready for TTS synthesis."""
+    text: str
+    voice_spec: str
+    enabled: bool
+
+
+def resolve_intro(
+    metadata: Optional[Dict[str, Any]],
+    original_filename: str,
+    read_title_intro: bool,
+    base_voice_spec: str,
+    job_voice: str,
+    voice_cache_keys: list[str],
+) -> IntroOutroSpec:
+    """Resolve the intro specification from job settings and metadata.
+
+    Returns an IntroOutroSpec with text and voice_spec populated,
+    or enabled=False if intro is disabled or text cannot be built.
+    """
+    if not read_title_intro:
+        return IntroOutroSpec(text="", voice_spec="", enabled=False)
+
+    text = build_title_intro_text(metadata, original_filename)
+    if not text:
+        return IntroOutroSpec(text="", voice_spec="", enabled=False)
+
+    voice_spec = resolve_fallback_voice_spec(
+        base_voice_spec, job_voice, voice_cache_keys
+    )
+    if not voice_spec:
+        return IntroOutroSpec(text=text, voice_spec="", enabled=False)
+
+    return IntroOutroSpec(text=text, voice_spec=voice_spec, enabled=True)
+
+
+def resolve_outro(
+    metadata: Optional[Dict[str, Any]],
+    original_filename: str,
+    read_closing_outro: bool,
+    base_voice_spec: str,
+    job_voice: str,
+    voice_cache_keys: list[str],
+) -> IntroOutroSpec:
+    """Resolve the outro specification from job settings and metadata.
+
+    Returns an IntroOutroSpec with text and voice_spec populated,
+    or enabled=False if outro is disabled or text cannot be built.
+    """
+    if not read_closing_outro:
+        return IntroOutroSpec(text="", voice_spec="", enabled=False)
+
+    text = build_outro_text(metadata, original_filename)
+    if not text:
+        return IntroOutroSpec(text="", voice_spec="", enabled=False)
+
+    voice_spec = resolve_fallback_voice_spec(
+        base_voice_spec, job_voice, voice_cache_keys
+    )
+    if not voice_spec:
+        return IntroOutroSpec(text=text, voice_spec="", enabled=False)
+
+    return IntroOutroSpec(text=text, voice_spec=voice_spec, enabled=True)

abogen/domain/metadata_extraction.py

@@ -0,0 +1,503 @@
+"""Metadata extraction and processing utilities.
+
+This module provides functions for extracting metadata from text content,
+formatting metadata tags for TTS embedding, and generating ffmpeg metadata arguments.
+"""
+
+from __future__ import annotations
+
+import datetime
+import logging
+import os
+import re
+import uuid
+from typing import Any, Dict, List, Optional, Tuple
+
+logger = logging.getLogger(__name__)
+
+
+def extract_metadata_from_text(text: str) -> Dict[str, Optional[str]]:
+    """Extract metadata tags from text content.
+    
+    Looks for tags in format: <<METADATA_KEY:value>>
+    
+    Supported tags:
+    - TITLE, ARTIST, ALBUM, YEAR
+    - ALBUM_ARTIST, COMPOSER, GENRE
+    - COVER_PATH
+    
+    Args:
+        text: Text content to search for metadata tags.
+        
+    Returns:
+        Dictionary with extracted metadata values (None if not found).
+    """
+    metadata = {}
+    
+    patterns = {
+        "title": r"<<METADATA_TITLE:([^>]*)>>",
+        "artist": r"<<METADATA_ARTIST:([^>]*)>>",
+        "album": r"<<METADATA_ALBUM:([^>]*)>>",
+        "year": r"<<METADATA_YEAR:([^>]*)>>",
+        "album_artist": r"<<METADATA_ALBUM_ARTIST:([^>]*)>>",
+        "composer": r"<<METADATA_COMPOSER:([^>]*)>>",
+        "genre": r"<<METADATA_GENRE:([^>]*)>>",
+        "cover_path": r"<<METADATA_COVER_PATH:([^>]*)>>",
+    }
+    
+    for key, pattern in patterns.items():
+        match = re.search(pattern, text)
+        if match:
+            metadata[key] = match.group(1).strip()
+        else:
+            metadata[key] = None
+    
+    return metadata
+
+
+def get_filename_from_path(
+    file_path: str,
+    display_path: Optional[str] = None,
+    from_queue: bool = False,
+) -> str:
+    """Extract filename (without extension) from path.
+    
+    Args:
+        file_path: The file path to extract from.
+        display_path: Optional display path (used if from_queue is False).
+        from_queue: Whether the file is from queue.
+        
+    Returns:
+        Filename without extension.
+    """
+    if from_queue:
+        base_path = file_path
+    else:
+        base_path = display_path if display_path else file_path
+    
+    filename = os.path.splitext(os.path.basename(base_path))[0]
+    return filename
+
+
+def build_ffmpeg_metadata_args(
+    metadata: Dict[str, Optional[str]],
+    filename: str,
+) -> List[str]:
+    """Build ffmpeg metadata arguments from metadata dictionary.
+    
+    Args:
+        metadata: Dictionary with metadata keys and values.
+        filename: Fallback filename for title/album if not specified.
+        
+    Returns:
+        List of ffmpeg metadata arguments.
+    """
+    args = []
+    
+    # Default values
+    defaults = {
+        "title": filename,
+        "artist": "Unknown",
+        "album": filename,
+        "date": str(datetime.datetime.now().year),
+        "album_artist": "Unknown",
+        "composer": "Narrator",
+        "genre": "Audiobook",
+    }
+    
+    # Map of metadata keys to ffmpeg metadata keys
+    key_mapping = {
+        "title": "title",
+        "artist": "artist",
+        "album": "album",
+        "year": "date",  # year -> date for ffmpeg
+        "album_artist": "album_artist",
+        "composer": "composer",
+        "genre": "genre",
+    }
+    
+    for metadata_key, ffmpeg_key in key_mapping.items():
+        value = metadata.get(metadata_key)
+        if value is None:
+            value = defaults.get(metadata_key, "")
+        if value:
+            args.extend(["-metadata", f"{ffmpeg_key}={value}"])
+    
+    return args
+
+
+def extract_metadata_and_build_args(
+    text: str,
+    filename: str,
+    display_path: Optional[str] = None,
+    from_queue: bool = False,
+) -> Tuple[List[str], Optional[str]]:
+    """Extract metadata from text and build ffmpeg arguments.
+    
+    Convenience function that combines extract_metadata_from_text and
+    build_ffmpeg_metadata_args.
+    
+    Args:
+        text: Text content to search for metadata tags.
+        filename: Fallback filename for title/album.
+        display_path: Optional display path.
+        from_queue: Whether the file is from queue.
+        
+    Returns:
+        Tuple of (ffmpeg_metadata_args, cover_path).
+    """
+    metadata = extract_metadata_from_text(text)
+    cover_path = metadata.get("cover_path")
+    
+    # Get actual filename from path
+    actual_filename = get_filename_from_path(
+        file_path=filename,
+        display_path=display_path,
+        from_queue=from_queue,
+    )
+    
+    args = build_ffmpeg_metadata_args(metadata, actual_filename)
+    return args, cover_path
+
+
+def read_text_for_metadata(
+    file_path: str,
+    is_direct_text: bool,
+    direct_text: Optional[str] = None,
+    encoding: Optional[str] = None,
+) -> str:
+    """Read text content for metadata extraction.
+    
+    Args:
+        file_path: Path to file (or text if is_direct_text).
+        is_direct_text: Whether file_path contains direct text.
+        direct_text: Optional direct text (used if is_direct_text).
+        encoding: File encoding (detected if not provided).
+        
+    Returns:
+        Text content for metadata extraction.
+    """
+    if is_direct_text:
+        return direct_text or file_path
+    
+    # Read from file
+    actual_path = direct_text if direct_text else file_path
+    
+    try:
+        if encoding is None:
+            from abogen.utils import detect_encoding
+            encoding = detect_encoding(actual_path)
+        
+        with open(actual_path, "r", encoding=encoding, errors="replace") as f:
+            return f.read()
+    except Exception:
+        return ""
+
+
+def extract_metadata_for_file(
+    file_path: str,
+    is_direct_text: bool = False,
+) -> Dict[str, Optional[str]]:
+    """Extract metadata dict from a file or direct text.
+
+    Convenience function combining read_text_for_metadata + extract_metadata_from_text.
+    Returns empty dict on any error.
+    """
+    try:
+        text = read_text_for_metadata(
+            file_path=file_path,
+            is_direct_text=is_direct_text,
+            direct_text=file_path if is_direct_text else None,
+        )
+        if text:
+            return extract_metadata_from_text(text) or {}
+    except Exception:
+        pass
+    return {}
+
+
+def format_metadata_tags(
+    metadata: Dict[str, Any],
+    filename: str,
+    chapter_count: int,
+    file_type: str,
+    cover_bytes: Optional[bytes] = None,
+    cache_dir: Optional[str] = None,
+) -> str:
+    """Format metadata tags for insertion into TTS text.
+
+    Builds <<METADATA_KEY:value>> tags that are later parsed by
+    extract_metadata_from_text() and fed to ffmpeg.
+
+    Args:
+        metadata: Dict with keys like 'title', 'authors' (list),
+            'publication_year', 'description', 'cover_image' (bytes).
+        filename: Fallback filename (without extension) for title/album.
+        chapter_count: Number of chapters/pages.
+        file_type: 'epub', 'pdf', or 'markdown'.
+        cover_bytes: Optional cover image bytes to save to cache.
+        cache_dir: Directory for cover cache (uses default if None).
+
+    Returns:
+        Newline-joined string of <<METADATA_KEY:value>> tags.
+    """
+    title = metadata.get("title") or filename
+    authors = metadata.get("authors") or ["Unknown"]
+    authors_text = ", ".join(authors) if isinstance(authors, list) else str(authors)
+    year = metadata.get("publication_year") or str(datetime.datetime.now().year)
+
+    chapter_label = "Chapters" if file_type in ("epub", "markdown") else "Pages"
+    chapter_text = f"{chapter_count} {chapter_label}"
+
+    tags = [
+        f"<<METADATA_TITLE:{title}>>",
+        f"<<METADATA_ARTIST:{authors_text}>>",
+        f"<<METADATA_ALBUM:{title} ({chapter_text})>>",
+        f"<<METADATA_YEAR:{year}>>",
+        f"<<METADATA_ALBUM_ARTIST:{authors_text}>>",
+        f"<<METADATA_COMPOSER:Narrator>>",
+        f"<<METADATA_GENRE:Audiobook>>",
+    ]
+
+    cover_path = _save_cover_to_cache(cover_bytes, cache_dir)
+    if cover_path:
+        tags.append(f"<<METADATA_COVER_PATH:{cover_path}>>")
+
+    return "\n".join(tags)
+
+
+def _save_cover_to_cache(
+    cover_bytes: Optional[bytes],
+    cache_dir: Optional[str] = None,
+) -> Optional[str]:
+    """Save cover image bytes to cache directory.
+
+    Args:
+        cover_bytes: Raw image bytes (e.g. JPEG/PNG).
+        cache_dir: Directory to save to. If None, returns None.
+
+    Returns:
+        Normalized path to saved cover file, or None on failure.
+    """
+    if not cover_bytes:
+        return None
+    if cache_dir is None:
+        return None
+
+    try:
+        cover_path = os.path.join(cache_dir, f"cover_{uuid.uuid4()}.jpg")
+        cover_path = os.path.normpath(cover_path)
+        with open(cover_path, "wb") as f:
+            f.write(cover_bytes)
+        return cover_path
+    except Exception as e:
+        logger.warning("Failed to save cover image: %s", e)
+        return None
+
+
+def extract_book_metadata_epub(book: Any) -> Dict[str, Any]:
+    """Extract metadata from an opened ebooklib EPUB book.
+
+    Args:
+        book: An opened ebooklib EPUB book object.
+
+    Returns:
+        Dict with keys: title, authors, description, publisher,
+        publication_year, cover_image (bytes or None).
+    """
+    import ebooklib
+
+    metadata: Dict[str, Any] = {
+        "title": None,
+        "authors": [],
+        "description": None,
+        "cover_image": None,
+        "publisher": None,
+        "publication_year": None,
+    }
+
+    try:
+        title_items = book.get_metadata("DC", "title")
+        if title_items and len(title_items) > 0:
+            metadata["title"] = title_items[0][0]
+    except Exception as e:
+        logger.warning("Error extracting title metadata: %s", e)
+
+    try:
+        author_items = book.get_metadata("DC", "creator")
+        if author_items:
+            metadata["authors"] = [
+                author[0] for author in author_items if len(author) > 0
+            ]
+    except Exception as e:
+        logger.warning("Error extracting author metadata: %s", e)
+
+    try:
+        desc_items = book.get_metadata("DC", "description")
+        if desc_items and len(desc_items) > 0:
+            metadata["description"] = desc_items[0][0]
+    except Exception as e:
+        logger.warning("Error extracting description metadata: %s", e)
+
+    try:
+        publisher_items = book.get_metadata("DC", "publisher")
+        if publisher_items and len(publisher_items) > 0:
+            metadata["publisher"] = publisher_items[0][0]
+    except Exception as e:
+        logger.warning("Error extracting publisher metadata: %s", e)
+
+    try:
+        date_items = book.get_metadata("DC", "date")
+        if date_items and len(date_items) > 0:
+            date_str = date_items[0][0]
+            year_match = re.search(r"\b(19|20)\d{2}\b", date_str)
+            if year_match:
+                metadata["publication_year"] = year_match.group(0)
+            else:
+                metadata["publication_year"] = date_str
+    except Exception as e:
+        logger.warning("Error extracting publication date metadata: %s", e)
+
+    for item in book.get_items_of_type(ebooklib.ITEM_COVER):
+        metadata["cover_image"] = item.get_content()
+        break
+
+    if not metadata["cover_image"]:
+        for item in book.get_items_of_type(ebooklib.ITEM_IMAGE):
+            if "cover" in item.get_name().lower():
+                metadata["cover_image"] = item.get_content()
+                break
+
+    return metadata
+
+
+def extract_book_metadata_pdf(pdf_doc: Any) -> Dict[str, Any]:
+    """Extract metadata from an opened PyMuPDF document.
+
+    Args:
+        pdf_doc: An opened fitz.Document object.
+
+    Returns:
+        Dict with keys: title, authors, description, publisher,
+        publication_year, cover_image (bytes or None).
+    """
+    metadata: Dict[str, Any] = {
+        "title": None,
+        "authors": [],
+        "description": None,
+        "cover_image": None,
+        "publisher": None,
+        "publication_year": None,
+    }
+
+    pdf_info = pdf_doc.metadata
+    if pdf_info:
+        metadata["title"] = pdf_info.get("title", None)
+        author = pdf_info.get("author", None)
+        if author:
+            metadata["authors"] = [author]
+        metadata["description"] = pdf_info.get("subject", None)
+        keywords = pdf_info.get("keywords", None)
+        if keywords:
+            if metadata["description"]:
+                metadata["description"] += f"\n\nKeywords: {keywords}"
+            else:
+                metadata["description"] = f"Keywords: {keywords}"
+        metadata["publisher"] = pdf_info.get("creator", None)
+
+        if "creationDate" in pdf_info:
+            date_str = pdf_info["creationDate"]
+            year_match = re.search(r"D:(\d{4})", date_str)
+            if year_match:
+                metadata["publication_year"] = year_match.group(1)
+        elif "modDate" in pdf_info:
+            date_str = pdf_info["modDate"]
+            year_match = re.search(r"D:(\d{4})", date_str)
+            if year_match:
+                metadata["publication_year"] = year_match.group(1)
+
+    if len(pdf_doc) > 0:
+        try:
+            import fitz
+            pix = pdf_doc[0].get_pixmap(matrix=fitz.Matrix(2, 2))
+            metadata["cover_image"] = pix.tobytes("png")
+        except Exception:
+            pass
+
+    return metadata
+
+
+def extract_book_metadata_markdown(
+    markdown_text: str,
+    markdown_toc: Optional[List[Dict[str, Any]]] = None,
+) -> Dict[str, Any]:
+    """Extract metadata from markdown frontmatter and first heading.
+
+    Args:
+        markdown_text: Raw markdown text content.
+        markdown_toc: Optional table of contents list (each item has
+            'level' and 'name' keys).
+
+    Returns:
+        Dict with keys: title, authors, description, publication_year.
+        cover_image is always None for markdown.
+    """
+    metadata: Dict[str, Any] = {
+        "title": None,
+        "authors": [],
+        "description": None,
+        "cover_image": None,
+        "publisher": None,
+        "publication_year": None,
+    }
+
+    if not markdown_text:
+        return metadata
+
+    frontmatter_match = re.match(
+        r"^---\s*\n(.*?)\n---\s*\n", markdown_text, re.DOTALL
+    )
+    if frontmatter_match:
+        try:
+            frontmatter = frontmatter_match.group(1)
+            title_match = re.search(
+                r"^title:\s*(.+)$", frontmatter, re.MULTILINE | re.IGNORECASE
+            )
+            if title_match:
+                metadata["title"] = title_match.group(1).strip().strip("\"'")
+
+            author_match = re.search(
+                r"^author:\s*(.+)$", frontmatter, re.MULTILINE | re.IGNORECASE
+            )
+            if author_match:
+                metadata["authors"] = [
+                    author_match.group(1).strip().strip("\"'")
+                ]
+
+            desc_match = re.search(
+                r"^description:\s*(.+)$", frontmatter, re.MULTILINE | re.IGNORECASE
+            )
+            if desc_match:
+                metadata["description"] = (
+                    desc_match.group(1).strip().strip("\"'")
+                )
+
+            date_match = re.search(
+                r"^date:\s*(.+)$", frontmatter, re.MULTILINE | re.IGNORECASE
+            )
+            if date_match:
+                date_str = date_match.group(1).strip().strip("\"'")
+                year_match = re.search(r"\b(19|20)\d{2}\b", date_str)
+                if year_match:
+                    metadata["publication_year"] = year_match.group(0)
+        except Exception as e:
+            logger.warning("Error parsing markdown frontmatter: %s", e)
+
+    if not metadata["title"] and markdown_toc:
+        first_h1 = next(
+            (h for h in markdown_toc if h.get("level") == 1), None
+        )
+        if first_h1:
+            metadata["title"] = first_h1.get("name")
+
+    return metadata

abogen/domain/metadata_helpers.py

@@ -0,0 +1,496 @@
+from __future__ import annotations
+
+import json
+import math
+import re
+from pathlib import Path
+from typing import Any, Dict, List, Mapping, Optional, Tuple
+
+
+_SERIES_NAME_KEYS = (
+    "series",
+    "series_name",
+    "series_title",
+)
+_SERIES_NUMBER_KEYS = (
+    "series_index",
+    "series_position",
+    "series_sequence",
+    "book_number",
+    "series_number",
+)
+_SERIES_NUMBER_RE = re.compile(r"\d+(?:\.\d+)?")
+
+_SERIES_NAME_ALIASES = ("series", "series_name", "seriesname", "series_title", "seriestitle")
+_SERIES_INDEX_ALIASES = ("series_index", "series_sequence", "series_position", "book_number")
+_AUTHOR_ALIASES = ("author", "authors")
+_DESCRIPTION_ALIASES = ("description", "summary")
+_TAGS_ALIASES = ("tags", "keywords", "genre")
+
+
+def expand_metadata_aliases(tags: Mapping[str, Any]) -> Dict[str, Any]:
+    """Expand concept aliases so each concept has all canonical keys set.
+
+    One input concept fans out to multiple keys so that downstream consumers
+    can look up any variant and find the value.
+
+    Expanded concepts:
+        series     -> series, series_name, seriesname, series_title, seriestitle
+        series_index -> series_index, series_sequence, series_position, book_number
+        author     -> author, authors
+        description -> description, summary
+        tags       -> tags, keywords, genre
+    """
+    if not tags:
+        return {}
+
+    result: Dict[str, Any] = {}
+    for key, value in tags.items():
+        if value is None:
+            continue
+        text = str(value).strip() if not isinstance(value, (list, tuple, set)) else value
+        if not text:
+            continue
+        key_lower = str(key).strip().lower()
+        if not key_lower:
+            continue
+
+        if key_lower in _SERIES_NAME_ALIASES:
+            for alias in _SERIES_NAME_ALIASES:
+                result[alias] = text
+        elif key_lower in _SERIES_INDEX_ALIASES:
+            for alias in _SERIES_INDEX_ALIASES:
+                result[alias] = text
+        elif key_lower in _AUTHOR_ALIASES:
+            for alias in _AUTHOR_ALIASES:
+                result[alias] = text
+        elif key_lower in _DESCRIPTION_ALIASES:
+            for alias in _DESCRIPTION_ALIASES:
+                result[alias] = text
+        elif key_lower in _TAGS_ALIASES:
+            for alias in _TAGS_ALIASES:
+                result[alias] = text
+        else:
+            result[key_lower] = text
+
+    return result
+
+
+def normalize_metadata_map(values: Optional[Mapping[str, Any]]) -> Dict[str, str]:
+    normalized: Dict[str, str] = {}
+    if not values:
+        return normalized
+    for key, value in values.items():
+        if value is None:
+            continue
+        text = str(value).strip()
+        if not text:
+            continue
+        normalized[str(key).casefold()] = text
+    return normalized
+
+
+def format_author_sentence(raw: Optional[str]) -> str:
+    if raw is None:
+        return ""
+    normalized = str(raw).strip()
+    if not normalized:
+        return ""
+    lowered = normalized.casefold()
+    if lowered in {"unknown", "various"}:
+        return ""
+
+    working = normalized.replace("&", " and ")
+    segments = [segment.strip() for segment in working.split(",") if segment.strip()]
+    tokens: List[str] = []
+
+    if segments:
+        for segment in segments:
+            parts = [part.strip() for part in re.split(r"\band\b", segment, flags=re.IGNORECASE) if part.strip()]
+            if parts:
+                tokens.extend(parts)
+            else:
+                tokens.append(segment)
+    else:
+        parts = [part.strip() for part in re.split(r"\band\b", working, flags=re.IGNORECASE) if part.strip()]
+        tokens.extend(parts or [normalized])
+
+    cleaned = [token for token in tokens if token and token.casefold() not in {"unknown", "various"}]
+    if not cleaned:
+        return ""
+    if len(cleaned) == 1:
+        return f"By {cleaned[0]}"
+    if len(cleaned) == 2:
+        return f"By {cleaned[0]} and {cleaned[1]}"
+    return f"By {', '.join(cleaned[:-1])}, and {cleaned[-1]}"
+
+
+def ensure_sentence(text: str) -> str:
+    cleaned = text.strip()
+    if not cleaned:
+        return ""
+    if cleaned[-1] in ".!?":
+        return cleaned
+    return f"{cleaned}."
+
+
+def normalize_series_number(value: Any) -> Optional[str]:
+    text = str(value or "").strip()
+    if not text:
+        return None
+    candidate = text.replace(",", ".")
+    if candidate.replace(".", "", 1).isdigit():
+        if "." in candidate:
+            normalized = candidate.rstrip("0").rstrip(".")
+            return normalized or "0"
+        try:
+            return str(int(candidate))
+        except ValueError:
+            pass
+    match = _SERIES_NUMBER_RE.search(candidate)
+    if not match:
+        return None
+    normalized = match.group(0)
+    if "." in normalized:
+        normalized = normalized.rstrip("0").rstrip(".")
+        return normalized or "0"
+    try:
+        return str(int(normalized))
+    except ValueError:
+        return normalized
+
+
+def extract_series_metadata(values: Mapping[str, str]) -> Tuple[Optional[str], Optional[str]]:
+    series_name: Optional[str] = None
+    for key in _SERIES_NAME_KEYS:
+        raw = values.get(key)
+        if raw:
+            cleaned = str(raw).strip()
+            if cleaned:
+                series_name = cleaned
+                break
+
+    series_number: Optional[str] = None
+    for key in _SERIES_NUMBER_KEYS:
+        raw = values.get(key)
+        if raw is None:
+            continue
+        normalized = normalize_series_number(raw)
+        if normalized:
+            series_number = normalized
+            break
+
+    return series_name, series_number
+
+
+def format_series_sentence(series_name: Optional[str], series_number: Optional[str]) -> str:
+    if not series_name or not series_number:
+        return ""
+    name = series_name.strip()
+    number = series_number.strip()
+    if not name or not number:
+        return ""
+    article = "the " if not name.lower().startswith("the ") else ""
+    phrase = f"Book {number} of {article}{name}"
+    return re.sub(r"\s+", " ", phrase).strip()
+
+
+_PEOPLE_SPLIT_RE = re.compile(r"[;,/&]|\band\b", re.IGNORECASE)
+_LIST_SPLIT_RE = re.compile(r"[;,\n]")
+_SERIES_SEQUENCE_TAG_KEYS: Tuple[str, ...] = (
+    "series_index",
+    "series_position",
+    "series_sequence",
+    "series_number",
+    "seriesnumber",
+    "book_number",
+    "booknumber",
+)
+
+
+def normalize_metadata_casefold(values: Optional[Mapping[str, Any]]) -> Dict[str, Any]:
+    normalized: Dict[str, Any] = {}
+    if not values:
+        return normalized
+    for key, value in values.items():
+        if value is None:
+            continue
+        key_text = str(key).strip().lower()
+        if not key_text:
+            continue
+        if isinstance(value, (list, tuple, set)):
+            normalized[key_text] = value
+        else:
+            text = str(value).strip()
+            if text:
+                normalized[key_text] = text
+    return normalized
+
+
+def split_people_field(raw: Any) -> List[str]:
+    if raw is None:
+        return []
+    if isinstance(raw, (list, tuple, set)):
+        results: List[str] = []
+        for item in raw:
+            results.extend(split_people_field(item))
+        return results
+    text = str(raw or "").strip()
+    if not text:
+        return []
+    tokens = [_token.strip() for _token in _PEOPLE_SPLIT_RE.split(text) if _token.strip()]
+    seen: set[str] = set()
+    ordered: List[str] = []
+    for token in tokens:
+        key = token.casefold()
+        if key in seen:
+            continue
+        seen.add(key)
+        ordered.append(token)
+    return ordered
+
+
+def split_simple_list(raw: Any) -> List[str]:
+    if raw is None:
+        return []
+    if isinstance(raw, (list, tuple, set)):
+        results: List[str] = []
+        for item in raw:
+            results.extend(split_simple_list(item))
+        return results
+    text = str(raw or "").strip()
+    if not text:
+        return []
+    tokens = [_token.strip() for _token in _LIST_SPLIT_RE.split(text) if _token.strip()]
+    seen: set[str] = set()
+    ordered: List[str] = []
+    for token in tokens:
+        key = token.casefold()
+        if key in seen:
+            continue
+        seen.add(key)
+        ordered.append(token)
+    return ordered
+
+
+def first_nonempty(*values: Any) -> Optional[str]:
+    for value in values:
+        if value is None:
+            continue
+        if isinstance(value, (list, tuple, set)):
+            items = list(value)
+            if not items:
+                continue
+            value = items[0]
+        text = str(value).strip()
+        if text:
+            return text
+    return None
+
+
+def extract_year(raw: Optional[str]) -> Optional[int]:
+    if not raw:
+        return None
+    text = str(raw).strip()
+    if not text:
+        return None
+    match = re.search(r"(19|20)\d{2}", text)
+    if match:
+        try:
+            return int(match.group(0))
+        except ValueError:
+            return None
+    try:
+        parsed = int(text)
+    except ValueError:
+        return None
+    if 0 < parsed < 3000:
+        return parsed
+    return None
+
+
+def normalize_series_sequence(raw: Any) -> Optional[str]:
+    if raw is None:
+        return None
+    if isinstance(raw, (int, float)):
+        if isinstance(raw, float) and (math.isnan(raw) or math.isinf(raw)):
+            return None
+        text = str(raw)
+    else:
+        text = str(raw).strip()
+    if not text:
+        return None
+    candidate = text.replace(",", ".")
+    match = _SERIES_NUMBER_RE.search(candidate)
+    if not match:
+        return None
+    normalized = match.group(0)
+    if "." in normalized:
+        normalized = normalized.rstrip("0").rstrip(".")
+        if not normalized:
+            normalized = "0"
+        return normalized
+    try:
+        return str(int(normalized))
+    except ValueError:
+        cleaned = normalized.lstrip("0")
+        return cleaned or "0"
+
+
+def build_audiobookshelf_metadata(
+    tags: Mapping[str, Any],
+    *,
+    language: str = "",
+    filename: str = "",
+) -> Dict[str, Any]:
+    normalized = normalize_metadata_casefold(tags)
+    title = first_nonempty(
+        normalized.get("title"),
+        normalized.get("book_title"),
+        normalized.get("name"),
+        normalized.get("album"),
+        filename,
+    )
+    authors = split_people_field(
+        normalized.get("authors")
+        or normalized.get("author")
+        or normalized.get("album_artist")
+        or normalized.get("artist")
+    )
+    narrators = split_people_field(normalized.get("narrators") or normalized.get("narrator"))
+    description = first_nonempty(
+        normalized.get("description"), normalized.get("summary"), normalized.get("comment")
+    )
+    genres = split_simple_list(normalized.get("genre"))
+    keywords = split_simple_list(normalized.get("tags") or normalized.get("keywords"))
+    lang = first_nonempty(normalized.get("language"), normalized.get("lang")) or language or ""
+    series_name = first_nonempty(
+        normalized.get("series"),
+        normalized.get("series_name"),
+        normalized.get("seriesname"),
+        normalized.get("series_title"),
+        normalized.get("seriestitle"),
+    )
+
+    series_sequence = None
+    for key in _SERIES_SEQUENCE_TAG_KEYS:
+        raw_value = normalized.get(key)
+        seq = normalize_series_sequence(raw_value)
+        if seq:
+            series_sequence = seq
+            break
+    if not series_name:
+        series_sequence = None
+
+    data: Dict[str, Any] = {
+        "title": title,
+        "subtitle": normalized.get("subtitle"),
+        "authors": authors,
+        "narrators": narrators,
+        "description": description,
+        "publisher": normalized.get("publisher"),
+        "genres": genres,
+        "tags": keywords,
+        "language": lang,
+        "publishedYear": extract_year(
+            normalized.get("published")
+            or normalized.get("publication_year")
+            or normalized.get("date")
+            or normalized.get("year")
+        ),
+        "seriesName": series_name,
+        "seriesSequence": series_sequence,
+        "isbn": first_nonempty(normalized.get("isbn"), normalized.get("asin")),
+    }
+    published_date = first_nonempty(
+        normalized.get("published"), normalized.get("publication_date"), normalized.get("date")
+    )
+    if published_date:
+        data["publishedDate"] = published_date
+
+    rating_text = first_nonempty(normalized.get("rating"), normalized.get("my_rating"))
+    if rating_text:
+        try:
+            data["rating"] = float(str(rating_text).strip())
+        except ValueError:
+            pass
+        rating_max_text = first_nonempty(
+            normalized.get("rating_max"), normalized.get("rating_scale")
+        )
+        if rating_max_text:
+            try:
+                data["ratingMax"] = float(str(rating_max_text).strip())
+            except ValueError:
+                pass
+
+    cleaned: Dict[str, Any] = {}
+    for key, value in data.items():
+        if value is None:
+            continue
+        if isinstance(value, str) and not value.strip():
+            continue
+        if isinstance(value, (list, tuple)) and not value:
+            continue
+        cleaned[key] = value
+    return cleaned
+
+
+def load_audiobookshelf_chapters(
+    metadata_path: Path,
+) -> Optional[List[Dict[str, Any]]]:
+    if not metadata_path.exists():
+        return None
+    try:
+        payload = json.loads(metadata_path.read_text(encoding="utf-8"))
+    except (OSError, json.JSONDecodeError):
+        return None
+    chapters = payload.get("chapters")
+    if not isinstance(chapters, list):
+        return None
+    cleaned: List[Dict[str, Any]] = []
+    for entry in chapters:
+        if not isinstance(entry, Mapping):
+            continue
+        title = first_nonempty(entry.get("title"), entry.get("original_title"))
+        start = entry.get("start")
+        end = entry.get("end")
+        if title and start is not None and end is not None:
+            cleaned.append({"title": str(title), "start": start, "end": end})
+    return cleaned or None
+
+
+def build_metadata_payload(
+    metadata: Optional[Dict[str, Any]] = None,
+    chapter_markers: Optional[List[Dict[str, Any]]] = None,
+    chunk_markers: Optional[List[Dict[str, Any]]] = None,
+    chunk_level: Optional[str] = None,
+    speaker_mode: Optional[str] = None,
+    speakers: Optional[Dict[str, Any]] = None,
+    generate_epub3: bool = False,
+) -> Dict[str, Any]:
+    """Build the canonical metadata payload dict for persistence and downstream use.
+
+    This is the single source of truth for metadata assembly. Both PyQt and WebUI
+    runners should call this instead of building the dict manually.
+
+    Args:
+        metadata: Normalized metadata tags dict.
+        chapter_markers: List of chapter marker dicts with title/start/end.
+        chunk_markers: List of chunk marker dicts.
+        chunk_level: Chunk granularity level (e.g. 'chapter', 'chunk').
+        speaker_mode: Speaker mode ('single', 'multi', etc.).
+        speakers: Speaker profile mapping.
+        generate_epub3: Whether EPUB3 generation is enabled.
+
+    Returns:
+        Complete metadata payload dict.
+    """
+    return {
+        "metadata": dict(metadata or {}),
+        "chapters": chapter_markers or [],
+        "chunks": chunk_markers or [],
+        "chunk_level": chunk_level,
+        "speaker_mode": speaker_mode,
+        "speakers": dict(speakers or {}),
+        "generate_epub3": generate_epub3,
+    }

abogen/domain/metadata_merge.py

@@ -0,0 +1,23 @@
+from __future__ import annotations
+
+from typing import Any, Dict, Optional
+
+
+def merge_metadata(
+    extracted: Optional[Dict[str, Any]],
+    overrides: Optional[Dict[str, Any]],
+) -> Dict[str, str]:
+    merged: Dict[str, str] = {}
+    if extracted:
+        for key, value in extracted.items():
+            if value is None:
+                continue
+            merged[str(key)] = str(value)
+    if overrides:
+        for key, value in overrides.items():
+            key_str = str(key)
+            if value is None:
+                merged.pop(key_str, None)
+            else:
+                merged[key_str] = str(value)
+    return merged

abogen/domain/metadata_overrides.py

@@ -0,0 +1,56 @@
+"""OPDS metadata normalization.
+
+Normalizes metadata keys from various OPDS/Calibre sources into
+a canonical set of overrides for the audiobook conversion pipeline.
+"""
+
+from __future__ import annotations
+
+from typing import Any, Dict, Mapping
+
+from abogen.domain.metadata_helpers import expand_metadata_aliases
+
+
+def normalize_opds_metadata(metadata_payload: Mapping[str, Any]) -> Dict[str, Any]:
+    """Normalize OPDS/Calibre metadata into canonical override keys.
+
+    Takes a metadata payload with various key aliases (e.g. 'series'/'series_name',
+    'tags'/'keywords', 'authors'/'creator') and returns a dict with all
+    concept aliases expanded.
+
+    Args:
+        metadata_payload: Raw metadata dict from OPDS/Calibre import.
+
+    Returns:
+        Dict with all canonical metadata key aliases expanded.
+    """
+    def _stringify(value: Any) -> str:
+        if value is None:
+            return ""
+        if isinstance(value, (list, tuple, set)):
+            parts = [str(item).strip() for item in value if item is not None]
+            return ", ".join(part for part in parts if part)
+        return str(value).strip()
+
+    # Map OPDS-specific keys to common concept keys before expansion
+    normalized_input: Dict[str, Any] = {}
+    for key, value in metadata_payload.items():
+        if value is None:
+            continue
+        key_lower = str(key).strip().lower()
+        if not key_lower:
+            continue
+        text = _stringify(value)
+        if not text:
+            continue
+
+        # Map OPDS-specific author aliases
+        if key_lower in ("creator", "dc_creator"):
+            normalized_input["author"] = text
+        # Map OPDS-specific subtitle aliases
+        elif key_lower in ("sub_title", "calibre_subtitle"):
+            normalized_input["subtitle"] = text
+        else:
+            normalized_input[key_lower] = text
+
+    return expand_metadata_aliases(normalized_input)

abogen/domain/normalization.py

@@ -0,0 +1,245 @@
+"""Text normalization convenience helpers.
+
+Provides both the simple ``normalize_text_for_pipeline`` (apostrophe + LLM only)
+and the comprehensive ``prepare_text_for_tts`` that chains all three normalization
+stages used during conversion: heteronym rules → pronunciation rules → pipeline
+normalization.  The latter is the single entry point that both the Web UI and
+PyQt Desktop GUI should use.
+
+Also provides ``TTSContext`` — a dataclass bundling all pre-compiled normalization
+resources so they can be created once and passed as a single object.
+"""
+
+from __future__ import annotations
+
+from dataclasses import dataclass, field
+from typing import Any, Callable, Dict, List, Mapping, Optional
+
+from abogen.domain.enums import Language
+from abogen.kokoro_text_normalization import (
+    ApostropheConfig,
+    normalize_for_pipeline as _normalize_for_pipeline,
+)
+from abogen.normalization_settings import (
+    build_apostrophe_config,
+    get_runtime_settings,
+    apply_overrides as _apply_overrides,
+)
+
+_BASE_APOSTROPHE_CONFIG = ApostropheConfig()
+
+
+@dataclass
+class TTSContext:
+    """Bundles pre-compiled normalization resources for TTS processing.
+
+    Created once per conversion job and passed to ``prepare_text_for_tts``
+    instead of threading 5 separate parameters.
+    """
+
+    split_pattern: str = r"(?<=[.!?\-])\s+"
+    pronunciation_rules: Optional[List[Dict[str, Any]]] = None
+    heteronym_rules: Optional[List[Dict[str, Any]]] = None
+    normalization_overrides: Optional[Mapping[str, Any]] = None
+    usage_counter: Dict[str, int] = field(default_factory=dict)
+
+    def normalize(self, text: str) -> str:
+        """Shorthand: normalize text using this context's compiled rules."""
+        return prepare_text_for_tts(
+            text,
+            heteronym_rules=self.heteronym_rules,
+            pronunciation_rules=self.pronunciation_rules,
+            normalization_overrides=self.normalization_overrides,
+            usage_counter=self.usage_counter,
+        )
+
+
+def normalize_text_for_pipeline(
+    text: str,
+    *,
+    normalization_overrides: Optional[Mapping[str, Any]] = None,
+) -> str:
+    """Normalize text using runtime settings with optional overrides."""
+    runtime_settings = get_runtime_settings()
+    if normalization_overrides:
+        runtime_settings = _apply_overrides(runtime_settings, normalization_overrides)
+    apostrophe_config = build_apostrophe_config(settings=runtime_settings, base=_BASE_APOSTROPHE_CONFIG)
+    return _normalize_for_pipeline(text, config=apostrophe_config, settings=runtime_settings)
+
+
+def prepare_text_for_tts(
+    text: str,
+    *,
+    heteronym_rules: Optional[List[Dict[str, Any]]] = None,
+    pronunciation_rules: Optional[List[Dict[str, Any]]] = None,
+    normalization_overrides: Optional[Mapping[str, Any]] = None,
+    usage_counter: Optional[Dict[str, int]] = None,
+) -> str:
+    """Apply the full text normalization pipeline before TTS synthesis.
+
+    Chains three stages in order:
+      1. Heteronym sentence rules (context-dependent pronunciation)
+      2. Pronunciation rules (token-level replacements)
+      3. Pipeline normalization (apostrophe handling, LLM normalization)
+
+    This is the **single entry point** that both the Web UI conversion runner
+    and the PyQt conversion thread should call before passing text to the TTS
+    backend.
+
+    Parameters
+    ----------
+    text:
+        Raw text to normalize.
+    heteronym_rules:
+        Compiled heteronym rules from ``compile_heteronym_sentence_rules``.
+    pronunciation_rules:
+        Compiled pronunciation rules from ``compile_pronunciation_rules``.
+    normalization_overrides:
+        User-level overrides for normalization settings (apostrophe mode, etc.).
+    usage_counter:
+        Mutable dict that tracks how many times each pronunciation override was
+        applied.  Passed through to ``apply_pronunciation_rules``.
+
+    Returns
+    -------
+    str
+        Fully normalized text ready for TTS.
+    """
+    from abogen.domain.pronunciation import (
+        apply_heteronym_sentence_rules,
+        apply_pronunciation_rules,
+    )
+
+    result = str(text or "")
+
+    if heteronym_rules:
+        result = apply_heteronym_sentence_rules(result, heteronym_rules)
+
+    if pronunciation_rules:
+        result = apply_pronunciation_rules(result, pronunciation_rules, usage_counter)
+
+    runtime_settings = get_runtime_settings()
+    if normalization_overrides:
+        runtime_settings = _apply_overrides(runtime_settings, normalization_overrides)
+    apostrophe_config = build_apostrophe_config(settings=runtime_settings, base=_BASE_APOSTROPHE_CONFIG)
+
+    return _normalize_for_pipeline(result, config=apostrophe_config, settings=runtime_settings)
+
+
+def build_tts_context(
+    *,
+    language: Language,
+    subtitle: "SubtitleConfig | str" = "Disabled",
+    pronunciation: Optional["PronunciationConfig"] = None,
+    speakers: Optional[Dict[str, Any]] = None,
+    usage_counter: Optional[Dict[str, int]] = None,
+    log_callback: Optional[Callable[[str, str], None]] = None,
+) -> TTSContext:
+    """Build a TTSContext from raw data. Single entry point for both UIs.
+
+    Loads normalization settings, applies overrides, validates configuration,
+    merges pronunciation overrides, and compiles all rules.
+
+    Args:
+        language: Language enum value.
+        subtitle: SubtitleConfig object or subtitle mode string.
+        pronunciation: PronunciationConfig with override rules.
+        speakers: Speaker profile mapping.
+        usage_counter: Mutable dict for tracking override usage.
+        log_callback: Callable(level, message) for warnings.
+
+    Returns:
+        TTSContext ready for text normalization.
+    """
+    from abogen.domain.config_types import PronunciationConfig, SubtitleConfig
+    from abogen.domain.enums import SubtitleMode
+    from abogen.domain.pronunciation import (
+        compile_heteronym_sentence_rules,
+        compile_pronunciation_rules,
+        merge_pronunciation_overrides,
+    )
+    from abogen.domain.split_pattern import get_split_pattern
+
+    def _log(msg: str, level: str = "warning") -> None:
+        if log_callback:
+            log_callback(level, msg)
+
+    # Resolve subtitle mode
+    if isinstance(subtitle, SubtitleConfig):
+        resolved_subtitle = subtitle.mode
+    else:
+        try:
+            resolved_subtitle = SubtitleMode.from_str(subtitle) if not isinstance(subtitle, SubtitleMode) else subtitle
+        except ValueError:
+            resolved_subtitle = SubtitleMode.DISABLED
+
+    # Resolve pronunciation config
+    if pronunciation is None:
+        pronunciation = PronunciationConfig()
+
+    # Get runtime normalization settings
+    runtime_settings = get_runtime_settings()
+
+    # Apply per-job normalization overrides
+    if pronunciation.normalization_overrides:
+        runtime_settings = _apply_overrides(runtime_settings, pronunciation.normalization_overrides)
+
+    # Build apostrophe config
+    apostrophe_config = build_apostrophe_config(settings=runtime_settings)
+
+    # Validate LLM apostrophe mode
+    apostrophe_mode = str(runtime_settings.get("normalization_apostrophe_mode", "spacy")).lower()
+    if apostrophe_mode == "llm":
+        from abogen.normalization_settings import build_llm_configuration
+        llm_config = build_llm_configuration(runtime_settings)
+        if not llm_config.is_configured():
+            raise RuntimeError(
+                "LLM-based apostrophe normalization is selected, but the LLM configuration is incomplete."
+            )
+
+    # Check for num2words availability
+    if apostrophe_config.convert_numbers:
+        try:
+            import num2words  # noqa: F401
+        except ImportError:
+            _log(
+                "Number normalization is enabled but 'num2words' library is not available. "
+                "Numbers will NOT be converted to words."
+            )
+
+    # Compute split pattern
+    if not isinstance(language, Language):
+        raise TypeError(f"language must be Language enum, got {type(language).__name__}: {language!r}")
+    split_pattern = get_split_pattern(language, resolved_subtitle)
+
+    # Merge pronunciation overrides
+    source = {
+        "pronunciation_overrides": pronunciation.pronunciation_overrides,
+        "manual_overrides": pronunciation.manual_overrides,
+        "speakers": speakers or {},
+        "language": language,
+    }
+    merged_overrides = merge_pronunciation_overrides(source)
+
+    # Compile rules
+    pronunciation_rules = compile_pronunciation_rules(merged_overrides)
+    heteronym_rules = compile_heteronym_sentence_rules(pronunciation.heteronym_overrides)
+
+    if heteronym_rules:
+        _log(
+            f"Applying {len(heteronym_rules)} heteronym override(s) during conversion.",
+            level="debug",
+        )
+    if pronunciation_rules:
+        _log(
+            f"Applying {len(pronunciation_rules)} pronunciation override(s) during conversion.",
+            level="debug",
+        )
+
+    return TTSContext(
+        split_pattern=split_pattern,
+        pronunciation_rules=pronunciation_rules,
+        heteronym_rules=heteronym_rules,
+        normalization_overrides=pronunciation.normalization_overrides,
+        usage_counter=usage_counter if usage_counter is not None else {},
+    )

abogen/domain/output_paths.py

@@ -0,0 +1,226 @@
+"""Output path resolution utilities.
+
+Pure functions for resolving output directories, building file paths,
+and computing project folder layouts.
+"""
+
+from __future__ import annotations
+
+import os
+import platform
+import re
+from datetime import datetime
+from pathlib import Path
+from typing import Callable, List, Optional, Tuple
+
+from abogen.text_extractor import ExtractedChapter
+
+
+_OUTPUT_SANITIZE_RE = re.compile(r"[^\w\-_.]+")
+
+# OS-specific illegal characters for filenames
+_WINDOWS_ILLEGAL_CHARS_RE = re.compile(r'[<>:"/\\|?*\x00-\x1f]')
+_MACOS_ILLEGAL_CHARS_RE = re.compile(r"[:]")
+_LINUX_ILLEGAL_CHARS_RE = re.compile(r"[/\x00]")
+_CONTROL_CHARS_RE = re.compile(r"[\x00-\x1f]")
+_UNIX_CONTROL_CHARS_RE = re.compile(r'[\x00-\x1f]')
+_RESERVED_NAMES = frozenset(
+    {"CON", "PRN", "AUX", "NUL"}
+    | {f"COM{i}" for i in range(1, 10)}
+    | {f"LPT{i}" for i in range(1, 10)}
+)
+
+
+def sanitize_name_for_os(name: str, is_folder: bool = True) -> str:
+    """Sanitize a filename or folder name based on the operating system.
+
+    Args:
+        name: The name to sanitize
+        is_folder: Whether this is a folder name (default: True)
+
+    Returns:
+        Sanitized name safe for the current OS
+    """
+    if not name:
+        return "audiobook"
+
+    system = platform.system()
+
+    if system == "Windows":
+        sanitized = _WINDOWS_ILLEGAL_CHARS_RE.sub("_", name)
+        sanitized = _CONTROL_CHARS_RE.sub("_", sanitized)
+        sanitized = sanitized.rstrip(". ")
+        if sanitized.upper() in _RESERVED_NAMES or sanitized.upper().split(".")[0] in _RESERVED_NAMES:
+            sanitized = f"_{sanitized}"
+    elif system == "Darwin":
+        sanitized = _MACOS_ILLEGAL_CHARS_RE.sub("_", name)
+        sanitized = _CONTROL_CHARS_RE.sub("_", sanitized)
+        if is_folder and sanitized.startswith("."):
+            sanitized = "_" + sanitized[1:]
+    else:
+        sanitized = _LINUX_ILLEGAL_CHARS_RE.sub("_", name)
+        sanitized = _UNIX_CONTROL_CHARS_RE.sub("_", sanitized)
+        if is_folder and sanitized.startswith("."):
+            sanitized = "_" + sanitized[1:]
+
+    if not sanitized or sanitized.strip() == "":
+        sanitized = "audiobook"
+
+    if len(sanitized) > 255:
+        sanitized = sanitized[:255].rstrip(". ")
+
+    return sanitized
+
+
+def slugify(title: str, index: int) -> str:
+    sanitized = re.sub(r"[^\w\-]+", "_", title.lower()).strip("_")
+    if not sanitized:
+        sanitized = f"chapter_{index:02d}"
+    return sanitized[:80]
+
+
+def sanitize_filename_for_chapter(title: str, index: int, max_len: int = 80) -> str:
+    """Sanitize a chapter name for use as a filename component.
+
+    Combines character sanitization, OS safety, and smart truncation
+    at word boundaries. Prepends zero-padded index prefix.
+
+    Args:
+        title: Raw chapter title.
+        index: 1-based chapter number for prefix.
+        max_len: Maximum length of the sanitized portion (excluding prefix).
+
+    Returns:
+        Sanitized string like "01_the_beginning".
+    """
+    # Remove non-word/non-space/non-hyphen chars, then collapse spaces/hyphens
+    sanitized = re.sub(r"[^\w\s\-]", "", title)
+    sanitized = re.sub(r"[\s\-]+", "_", sanitized).strip("_")
+
+    if not sanitized:
+        sanitized = f"chapter_{index:02d}"
+
+    # OS-specific sanitization
+    system = platform.system()
+    if system == "Windows":
+        sanitized = _WINDOWS_ILLEGAL_CHARS_RE.sub("_", sanitized)
+        sanitized = sanitized.rstrip(". ")
+        base = sanitized.split(".")[0].upper()
+        if base in _RESERVED_NAMES:
+            sanitized = f"_{sanitized}"
+    # Linux: only NUL is truly illegal, but control chars are problematic
+    sanitized = _UNIX_CONTROL_CHARS_RE.sub("_", sanitized)
+
+    # Smart truncation at word boundary
+    if len(sanitized) > max_len:
+        pos = sanitized[:max_len].rfind("_")
+        sanitized = sanitized[: pos if pos > 0 else max_len].rstrip("_")
+
+    return f"{index:02d}_{sanitized}"
+
+
+def sanitize_output_stem(name: str, index: int = 0) -> str:
+    base = Path(name or "").stem
+    sanitized = _OUTPUT_SANITIZE_RE.sub("_", base).strip("_")
+    return sanitized or "output"
+
+
+def output_timestamp_token() -> str:
+    return datetime.now().strftime("%Y%m%d-%H%M%S")
+
+
+def build_output_path(directory: Path, original_name: str, extension: str) -> Path:
+    sanitized = sanitize_output_stem(original_name)
+    return directory / f"{sanitized}.{extension}"
+
+
+def apply_newline_policy(chapters: List[ExtractedChapter], replace_single_newlines: bool) -> None:
+    if not replace_single_newlines:
+        return
+    newline_regex = re.compile(r"(?<!\n)\n(?!\n)")
+    for chapter in chapters:
+        chapter.text = newline_regex.sub(" ", chapter.text)
+
+
+from abogen.domain.enums import SaveMode
+
+
+def resolve_output_directory(
+    *,
+    save_mode: str,
+    stored_path: Path,
+    output_folder: Optional[str],
+    desktop_dir: Optional[Path],
+    user_output_path: Optional[Path],
+    user_cache_outputs: Optional[Path],
+) -> Path:
+    if save_mode in (SaveMode.SAVE_TO_DESKTOP, "Save to Desktop") and desktop_dir:
+        return desktop_dir
+    if save_mode in (SaveMode.SAVE_NEXT_TO_INPUT, "Save next to input file"):
+        return stored_path.parent
+    if save_mode in (SaveMode.CHOOSE_OUTPUT_FOLDER, "Choose output folder") and output_folder:
+        return Path(output_folder)
+    if save_mode in (SaveMode.DEFAULT_OUTPUT, "Use default save location") and user_output_path:
+        return user_output_path
+    return user_cache_outputs or Path(".")
+
+
+def resolve_project_layout(
+    *,
+    original_filename: str,
+    save_as_project: bool,
+    base_dir: Path,
+    timestamp_fn: Callable[[], str] = output_timestamp_token,
+    sanitize_fn: Callable[[str, int], str] = sanitize_output_stem,
+) -> Tuple[Path, Path, Path, Optional[Path]]:
+    sanitized = sanitize_fn(original_filename, 0)
+    folder_name = f"{timestamp_fn()}_{sanitized}"
+    project_root = base_dir / folder_name
+    project_root.mkdir(parents=True, exist_ok=True)
+
+    if save_as_project:
+        audio_dir = project_root / "audio"
+        subtitle_dir = project_root / "subtitles"
+        metadata_dir = project_root / "metadata"
+        for directory in (audio_dir, subtitle_dir, metadata_dir):
+            directory.mkdir(parents=True, exist_ok=True)
+        return project_root, audio_dir, subtitle_dir, metadata_dir
+
+    return project_root, project_root, project_root, None
+
+
+def resolve_unique_path(
+    parent_dir: str,
+    base_name: str,
+    extension: str,
+    allowed_extensions: Optional[set] = None,
+) -> str:
+    """Find a unique file path by appending _2, _3, etc. on collision.
+
+    Args:
+        parent_dir: Directory to check for collisions.
+        base_name: Base filename (without extension).
+        extension: File extension (without dot).
+        allowed_extensions: Set of extensions to check against.
+            If None, checks any existing file/dir with same name.
+
+    Returns:
+        Full path without extension (e.g. "/path/to/name_2").
+    """
+    sanitized = sanitize_name_for_os(base_name, is_folder=True)
+    counter = 1
+    while True:
+        suffix = f"_{counter}" if counter > 1 else ""
+        candidate = os.path.join(parent_dir, f"{sanitized}{suffix}")
+        if allowed_extensions is not None:
+            file_parts = (os.path.splitext(f) for f in os.listdir(parent_dir))
+            clash = any(
+                name == f"{sanitized}{suffix}"
+                and ext[1:].lower() in allowed_extensions
+                for name, ext in file_parts
+            )
+        else:
+            clash = os.path.exists(candidate)
+        if not clash:
+            return candidate
+        counter += 1

abogen/domain/pipeline_factory.py

@@ -0,0 +1,117 @@
+"""Pipeline creation, caching and lifecycle management.
+
+Provides a unified interface for creating and managing TTS pipelines
+across all UI layers (WebUI, PyQt, CLI).
+
+Language handling: the engine owns the mapping between Language enum
+and its internal format. Callers pass Language enum; the engine
+converts internally. No engine-specific codes leak outside the engine.
+"""
+
+from __future__ import annotations
+
+from typing import Any, Dict
+
+from abogen.domain.device import select_device
+from abogen.domain.enums import Language
+from abogen.domain.voice_resolution import initialize_voice_cache
+from abogen.tts_plugin.utils import create_pipeline, is_plugin_registered
+
+
+def resolve_device(use_gpu: bool) -> str:
+    """Determine compute device from job and global config flags."""
+    from abogen.utils import load_config
+
+    cfg = load_config()
+    if use_gpu and cfg.get("use_gpu", True):
+        return select_device()
+    return "cpu"
+
+
+def create_pipeline_for_job(
+    provider: str,
+    language: Language,
+    use_gpu: bool,
+) -> Any:
+    """Create a TTS pipeline with proper device selection.
+
+    Args:
+        provider: TTS provider name ("kokoro" or "supertonic").
+        language: Language enum (app-layer type, not engine-specific).
+        use_gpu: Whether GPU acceleration is requested.
+    """
+    provider = str(provider or "kokoro").strip().lower() or "kokoro"
+    if not is_plugin_registered(provider):
+        provider = "kokoro"
+
+    if provider == "supertonic":
+        return create_pipeline("supertonic", language=language)
+
+    device = resolve_device(use_gpu)
+    return create_pipeline("kokoro", language=language, device=device)
+
+
+def dispose_pipelines(pipelines: Dict[str, Any]) -> None:
+    """Dispose all pipelines in a dict and clear it."""
+    for p in pipelines.values():
+        try:
+            p.dispose()
+        except Exception:
+            pass
+    pipelines.clear()
+
+
+class PipelinePool:
+    """Cache and manage TTS pipelines by provider.
+
+    Usage::
+
+        pool = PipelinePool()
+        backend = pool.get("kokoro", Language.EN_US, use_gpu=True)
+        # ... use backend ...
+        pool.dispose_all()
+    """
+
+    def __init__(self) -> None:
+        self._pipelines: Dict[str, Any] = {}
+        self._voice_cache_initialized = False
+
+    def get(
+        self,
+        provider: str,
+        language: Language,
+        use_gpu: bool,
+        *,
+        request: Any = None,
+        events: Any = None,
+    ) -> Any:
+        """Get or create a cached pipeline for the given provider.
+
+        Args:
+            provider: TTS provider name ("kokoro" or "supertonic").
+            language: Language enum (app-layer type).
+            use_gpu: Whether GPU acceleration is requested.
+            request: ConversionRequest for voice cache initialization.
+            events: ConversionEvents for logging during cache init.
+        """
+        provider = str(provider or "kokoro").strip().lower() or "kokoro"
+        if not is_plugin_registered(provider):
+            provider = "kokoro"
+
+        existing = self._pipelines.get(provider)
+        if existing is not None:
+            return existing
+
+        pipeline = create_pipeline_for_job(provider, language, use_gpu)
+        self._pipelines[provider] = pipeline
+
+        if provider == "kokoro" and not self._voice_cache_initialized and request is not None:
+            initialize_voice_cache(request, events=events)
+            self._voice_cache_initialized = True
+
+        return pipeline
+
+    def dispose_all(self) -> None:
+        """Dispose all cached pipelines."""
+        dispose_pipelines(self._pipelines)
+        self._voice_cache_initialized = False

abogen/domain/progress.py

@@ -0,0 +1,72 @@
+from __future__ import annotations
+
+"""Progress and ETR (estimated time remaining) calculation.
+
+Shared by Web UI and PyQt desktop GUI. Pure math, no UI dependencies.
+"""
+import time
+from dataclasses import dataclass, field
+
+
+@dataclass
+class ProgressTracker:
+    """Tracks character-based progress with ETR calculation.
+
+    Usage:
+        tracker = ProgressTracker(total_chars=50000)
+        # ... as processing occurs:
+        tracker.update(chars_done=5000)
+        print(tracker.etr_str)   # "00:04:30"
+        print(tracker.percent)   # 10
+    """
+    total_chars: int
+    _start_time: float = field(default_factory=time.time, repr=False)
+    _chars_done: int = field(default=0, repr=False)
+
+    def update(self, chars_done: int) -> None:
+        self._chars_done = chars_done
+
+    @property
+    def percent(self) -> int:
+        if self.total_chars <= 0:
+            return 0
+        return min(int(self._chars_done / self.total_chars * 100), 99)
+
+    @property
+    def etr_str(self) -> str:
+        elapsed = time.time() - self._start_time
+        if self._chars_done <= 0 or elapsed <= 0.5:
+            return "Processing..."
+        avg_time_per_char = elapsed / self._chars_done
+        remaining = self.total_chars - self._chars_done
+        if remaining <= 0:
+            return "00:00:00"
+        secs = avg_time_per_char * remaining
+        h = int(secs // 3600)
+        m = int((secs % 3600) // 60)
+        s = int(secs % 60)
+        return f"{h:02d}:{m:02d}:{s:02d}"
+
+
+def calc_etr_str(elapsed: float, done: int, total: int) -> str:
+    """Standalone ETR string calculation (matches PyQt original logic).
+
+    Args:
+        elapsed: seconds since processing started
+        done: items/characters processed so far
+        total: total items/characters to process
+
+    Returns:
+        ETR string like "01:23:45" or "Processing..."
+    """
+    if done <= 0 or elapsed <= 0.5:
+        return "Processing..."
+    avg_time_per_item = elapsed / done
+    remaining = total - done
+    if remaining <= 0:
+        return "00:00:00"
+    secs = avg_time_per_item * remaining
+    h = int(secs // 3600)
+    m = int((secs % 3600) // 60)
+    s = int(secs % 60)
+    return f"{h:02d}:{m:02d}:{s:02d}"

abogen/domain/pronunciation.py

@@ -0,0 +1,270 @@
+"""Pronunciation rule compilation and application.
+
+Pure functions for compiling token-level and sentence-level pronunciation
+overrides into regex patterns, applying them to text, and merging multiple
+override sources with precedence rules.
+"""
+
+from __future__ import annotations
+
+import re
+from typing import Any, Dict, Iterable, List, Mapping, Optional
+
+from abogen.entity_analysis import normalize_token as normalize_entity_token
+from abogen.entity_analysis import normalize_manual_override_token
+
+
+def compile_pronunciation_rules(
+    overrides: Optional[Iterable[Mapping[str, Any]]],
+) -> List[Dict[str, Any]]:
+    if not overrides:
+        return []
+
+    candidates: List[Dict[str, Any]] = []
+    seen: set[str] = set()
+
+    for entry in overrides:
+        if not isinstance(entry, Mapping):
+            continue
+        pronunciation_value = str(entry.get("pronunciation") or "").strip()
+        if not pronunciation_value:
+            continue
+
+        token_values: List[str] = []
+        token_raw = entry.get("token")
+        if token_raw:
+            token_value = str(token_raw).strip()
+            if token_value:
+                token_values.append(token_value)
+        normalized_raw = entry.get("normalized")
+        if normalized_raw:
+            normalized_value = str(normalized_raw).strip()
+            if normalized_value:
+                token_values.append(normalized_value)
+        if token_raw and not token_values:
+            fallback = normalize_entity_token(str(token_raw))
+            if fallback:
+                token_values.append(fallback)
+
+        if not token_values:
+            continue
+
+        usage_normalized = str(entry.get("normalized") or "").strip()
+        if not usage_normalized and token_values:
+            usage_normalized = normalize_entity_token(token_values[0]) or token_values[0]
+        usage_token = str(entry.get("token") or token_values[0])
+
+        for token_value in token_values:
+            key = token_value.casefold()
+            if key in seen:
+                continue
+            seen.add(key)
+            candidates.append(
+                {
+                    "token": token_value,
+                    "normalized": usage_normalized,
+                    "replacement": pronunciation_value,
+                }
+            )
+
+    if not candidates:
+        return []
+
+    candidates.sort(key=lambda item: len(item["token"]), reverse=True)
+    compiled: List[Dict[str, Any]] = []
+    for candidate in candidates:
+        token_value = candidate["token"]
+        pronunciation_value = candidate["replacement"]
+        escaped = re.escape(token_value)
+        pattern = re.compile(rf"(?i)(?<!\w){escaped}(?P<possessive>'s|\u2019s|\u2019)?(?!\w)")
+        compiled.append(
+            {
+                "pattern": pattern,
+                "replacement": pronunciation_value,
+                "normalized": candidate.get("normalized") or token_value,
+                "token": candidate.get("token") or token_value,
+            }
+        )
+
+    return compiled
+
+
+def compile_heteronym_sentence_rules(
+    overrides: Optional[Iterable[Mapping[str, Any]]],
+) -> List[Dict[str, Any]]:
+    if not overrides:
+        return []
+
+    compiled: List[Dict[str, Any]] = []
+    seen: set[str] = set()
+
+    for entry in overrides:
+        if not isinstance(entry, Mapping):
+            continue
+        sentence = str(entry.get("sentence") or "").strip()
+        if not sentence:
+            continue
+        choice = str(entry.get("choice") or "").strip()
+        if not choice:
+            continue
+
+        replacement_sentence = ""
+        options = entry.get("options")
+        if isinstance(options, list):
+            for opt in options:
+                if not isinstance(opt, Mapping):
+                    continue
+                if str(opt.get("key") or "").strip() == choice:
+                    replacement_sentence = str(opt.get("replacement_sentence") or "").strip()
+                    break
+        if not replacement_sentence:
+            continue
+
+        rule_key = f"{sentence}\n{choice}".casefold()
+        if rule_key in seen:
+            continue
+        seen.add(rule_key)
+
+        parts = [p for p in re.split(r"\s+", sentence) if p]
+        if not parts:
+            continue
+        pattern_text = r"\s+".join(re.escape(p) for p in parts)
+        pattern = re.compile(pattern_text)
+        compiled.append({"pattern": pattern, "replacement": replacement_sentence})
+
+    compiled.sort(key=lambda item: len(item["pattern"].pattern), reverse=True)
+    return compiled
+
+
+def apply_heteronym_sentence_rules(text: str, rules: List[Dict[str, Any]]) -> str:
+    if not text or not rules:
+        return text
+    result = text
+    for rule in rules:
+        pattern = rule["pattern"]
+        replacement = rule["replacement"]
+        result = pattern.sub(replacement, result)
+    return result
+
+
+def apply_pronunciation_rules(
+    text: str,
+    rules: List[Dict[str, Any]],
+    usage_counter: Optional[Dict[str, int]] = None,
+) -> str:
+    if not text or not rules:
+        return text
+
+    result = text
+    for rule in rules:
+        pattern = rule["pattern"]
+        pronunciation_value = rule["replacement"]
+        usage_key = str(rule.get("normalized") or "").strip()
+
+        def _replacement(match: re.Match[str]) -> str:
+            suffix = match.group("possessive") or ""
+            if usage_counter is not None and usage_key:
+                usage_counter[usage_key] = usage_counter.get(usage_key, 0) + 1
+            return pronunciation_value + suffix
+
+        result = pattern.sub(_replacement, result)
+
+    return result
+
+
+def merge_pronunciation_overrides(job: Any) -> List[Dict[str, Any]]:
+    """Return pronunciation override entries, ensuring manual overrides are included.
+
+    Pending jobs keep both ``manual_overrides`` and ``pronunciation_overrides``, but the
+    latter can be stale if the UI didn't resync before enqueue. During conversion,
+    we must merge manual overrides so they always apply (before TTS).
+
+    Precedence: manual overrides win over existing entries for the same normalized key.
+
+    Args:
+        job: Either a job-like object with attributes, or a dict with keys:
+            ``pronunciation_overrides``, ``manual_overrides``, ``speakers``, ``language``.
+    """
+
+    collected: Dict[str, Dict[str, Any]] = {}
+
+    def _get(key: str, default: Any = None) -> Any:
+        if isinstance(job, Mapping):
+            return job.get(key, default)
+        return getattr(job, key, default)
+
+    existing = _get("pronunciation_overrides")
+    if isinstance(existing, list):
+        for entry in existing:
+            if not isinstance(entry, Mapping):
+                continue
+            token_value = str(entry.get("token") or "").strip()
+            pronunciation_value = str(entry.get("pronunciation") or "").strip()
+            if not token_value or not pronunciation_value:
+                continue
+            normalized = str(entry.get("normalized") or "").strip() or normalize_entity_token(token_value)
+            if not normalized:
+                continue
+            collected[normalized] = {
+                "token": token_value,
+                "normalized": normalized,
+                "pronunciation": pronunciation_value,
+                "voice": str(entry.get("voice") or "").strip() or None,
+                "notes": str(entry.get("notes") or "").strip() or None,
+                "context": str(entry.get("context") or "").strip() or None,
+                "source": str(entry.get("source") or "pronunciation"),
+                "language": _get("language"),
+            }
+
+    speakers = _get("speakers")
+    if isinstance(speakers, dict):
+        for payload in speakers.values():
+            if not isinstance(payload, Mapping):
+                continue
+            token_value = str(payload.get("token") or "").strip()
+            pronunciation_value = str(payload.get("pronunciation") or "").strip()
+            if not token_value or not pronunciation_value:
+                continue
+            normalized = normalize_entity_token(token_value)
+            if not normalized:
+                continue
+            collected[normalized] = {
+                "token": token_value,
+                "normalized": normalized,
+                "pronunciation": pronunciation_value,
+                "voice": str(
+                    payload.get("resolved_voice")
+                    or payload.get("voice")
+                    or _get("voice", "")
+                ).strip()
+                or None,
+                "notes": None,
+                "context": None,
+                "source": "speaker",
+                "language": _get("language"),
+            }
+
+    manual = _get("manual_overrides")
+    if isinstance(manual, list):
+        for entry in manual:
+            if not isinstance(entry, Mapping):
+                continue
+            token_value = str(entry.get("token") or "").strip()
+            pronunciation_value = str(entry.get("pronunciation") or "").strip()
+            if not token_value or not pronunciation_value:
+                continue
+            normalized = str(entry.get("normalized") or "").strip() or normalize_manual_override_token(token_value)
+            if not normalized:
+                continue
+            collected[normalized] = {
+                "token": token_value,
+                "normalized": normalized,
+                "pronunciation": pronunciation_value,
+                "voice": str(entry.get("voice") or "").strip() or None,
+                "notes": str(entry.get("notes") or "").strip() or None,
+                "context": str(entry.get("context") or "").strip() or None,
+                "source": str(entry.get("source") or "manual"),
+                "language": _get("language"),
+            }
+
+    return list(collected.values())

abogen/domain/settings_core.py

@@ -0,0 +1,641 @@
+"""Shared settings core.
+
+Defines the SETTINGS_REGISTRY — the single source of truth for all settings.
+Every setting has a key, type, default, validation rules, and UI scope.
+Both Web UI and Desktop GUI must reference this registry.
+"""
+
+from __future__ import annotations
+
+import os
+import re
+from dataclasses import dataclass
+from typing import Any, Callable, Dict, Mapping, Optional
+
+from abogen.constants import (
+    KOKORO_CODE_LABELS,
+    SUBTITLE_FORMATS,
+    SUPPORTED_SOUND_FORMATS,
+)
+from abogen.tts_plugin.utils import get_default_voice
+from abogen.normalization_settings import (
+    DEFAULT_LLM_PROMPT,
+    environment_llm_defaults,
+)
+
+
+# ── Schema ───────────────────────────────────────────────────────────
+
+@dataclass(frozen=True)
+class Setting:
+    """Contract for a single setting.
+
+    Attributes:
+        key: Config dict key (e.g. "output_format").
+        type_: Python type (bool, int, float, str, list).
+        default: Default value or callable returning one.
+        min_value: Minimum for numeric types.
+        max_value: Maximum for numeric types.
+        valid_values: Allowed values for str types (None = any).
+        gui_only: True if only used by PyQt Desktop GUI.
+        web_only: True if only used by Web UI.
+        normalizer: Optional callable(value, default) -> normalized_value.
+        description: Human-readable explanation.
+    """
+    key: str
+    type_: type
+    default: Any
+    min_value: float | None = None
+    max_value: float | None = None
+    valid_values: tuple[Any, ...] | None = None
+    gui_only: bool = False
+    web_only: bool = False
+    normalizer: Callable | None = None
+    description: str = ""
+
+    def coerce(self, value: Any, fallback: Any | None = None) -> Any:
+        """Coerce value to the declared type, returning fallback on failure."""
+        fb = fallback if fallback is not None else self.default
+        if self.type_ is bool:
+            if isinstance(value, bool):
+                return value
+            if isinstance(value, str):
+                return value.lower() in {"true", "1", "yes", "on"}
+            if value is None:
+                return fb
+            return bool(value)
+        if self.type_ is int:
+            try:
+                v = int(value)
+            except (TypeError, ValueError):
+                return fb
+            if self.min_value is not None:
+                v = max(int(self.min_value), v)
+            if self.max_value is not None:
+                v = min(int(self.max_value), v)
+            return v
+        if self.type_ is float:
+            try:
+                v = float(value)
+            except (TypeError, ValueError):
+                return fb
+            if self.min_value is not None:
+                v = max(self.min_value, v)
+            if self.max_value is not None:
+                v = min(self.max_value, v)
+            return v
+        if self.type_ is str:
+            if isinstance(value, str):
+                v = value.strip()
+                if self.valid_values and v not in self.valid_values:
+                    return fb
+                return v
+            return fb
+        if self.type_ is list:
+            if isinstance(value, (list, tuple, set)):
+                return list(value)
+            return fb
+        return value
+
+
+# ── Normalizers (used by Setting.normalizer) ─────────────────────────
+
+def _norm_save_mode(value: Any, default: str) -> str:
+    if isinstance(value, str):
+        if value in SAVE_MODE_LABELS:
+            return value
+        if value in LEGACY_SAVE_MODE_MAP:
+            return LEGACY_SAVE_MODE_MAP[value]
+    return default
+
+
+def _norm_voice_spec(value: Any, default: str) -> str:
+    if isinstance(value, str):
+        text = value.strip()
+        if not text:
+            return default
+        spec, profile_name = split_profile_spec(text)
+        if profile_name:
+            return f"speaker:{profile_name}"
+        return spec
+    return default
+
+
+def _norm_speaker_spec(value: Any, default: str) -> str:
+    if isinstance(value, str):
+        text = value.strip()
+        if not text:
+            return ""
+        spec, profile_name = split_profile_spec(text)
+        if profile_name:
+            return f"speaker:{profile_name}"
+        return spec
+    return ""
+
+
+def _norm_language_list(value: Any, default: list) -> list:
+    if isinstance(value, (list, tuple, set)):
+        return [code for code in value if isinstance(code, str) and code in KOKORO_CODE_LABELS]
+    if isinstance(value, str):
+        parts = [item.strip().lower() for item in value.split(",") if item.strip()]
+        return [code for code in parts if code in KOKORO_CODE_LABELS]
+    return default
+
+
+def _norm_stripped_str(value: Any, default: str) -> str:
+    return str(value or "").strip()
+
+
+def _norm_prompt(value: Any, default: str) -> str:
+    candidate = str(value or "").strip()
+    return candidate if candidate else default
+
+
+# ── Registry ─────────────────────────────────────────────────────────
+
+def _default_output_format() -> str:
+    return "wav"
+
+
+def _default_save_mode() -> str:
+    return "default_output" if has_output_override() else "save_next_to_input"
+
+
+def _default_llm(key: str) -> str:
+    return environment_llm_defaults().get(key, "")
+
+
+SETTINGS_REGISTRY: list[Setting] = [
+    # ── Core output ──────────────────────────────────────────────
+    Setting("output_format", str, "wav",
+            valid_values=tuple(SUPPORTED_SOUND_FORMATS),
+            description="Audio output format"),
+    Setting("subtitle_format", str, "srt",
+            valid_values=tuple(item[0] for item in SUBTITLE_FORMATS),
+            description="Subtitle file format"),
+    Setting("save_mode", str, _default_save_mode,
+            normalizer=_norm_save_mode,
+            description="Where to save output files"),
+    Setting("separate_chapters_format", str, "wav",
+            valid_values=("wav", "flac", "mp3", "opus"),
+            description="Format for separately saved chapters"),
+    Setting("chunk_level", str, "paragraph",
+            valid_values=("paragraph", "sentence"),
+            description="Text chunking granularity"),
+
+    # ── Voice ────────────────────────────────────────────────────
+    Setting("default_speaker", str, "",
+            normalizer=_norm_speaker_spec,
+            description="Default speaker name"),
+    Setting("default_voice", str, lambda: get_default_voice("kokoro"),
+            normalizer=_norm_voice_spec,
+            description="Default TTS voice"),
+    Setting("speed", float, 1.0, min_value=0.5, max_value=3.0,
+            gui_only=True,
+            description="TTS speed multiplier"),
+    Setting("supertonic_total_steps", int, 5, min_value=2, max_value=15,
+            description="SuperTonic processing steps"),
+    Setting("supertonic_speed", float, 1.0, min_value=0.7, max_value=2.0,
+            description="SuperTonic speed"),
+
+    # ── Chapter handling ─────────────────────────────────────────
+    Setting("silence_between_chapters", float, 2.0, min_value=0.0,
+            description="Silence gap between chapters (seconds)"),
+    Setting("chapter_intro_delay", float, 0.5, min_value=0.0,
+            description="Delay after chapter heading (seconds)"),
+    Setting("read_title_intro", bool, False,
+            description="Read chapter title as intro"),
+    Setting("read_closing_outro", bool, True,
+            description="Read closing/outro text"),
+    Setting("normalize_chapter_opening_caps", bool, True,
+            description="Normalize chapter opening caps"),
+    Setting("auto_prefix_chapter_titles", bool, True,
+            description="Auto-prefix chapter titles"),
+    Setting("save_chapters_separately", bool, False,
+            description="Save each chapter as separate file"),
+    Setting("merge_chapters_at_end", bool, True,
+            description="Merge chapters into single file"),
+    Setting("save_as_project", bool, False,
+            description="Save as editable project"),
+    Setting("generate_epub3", bool, False,
+            description="Generate EPUB3 output"),
+
+    # ── GPU / performance ────────────────────────────────────────
+    Setting("use_gpu", bool, True,
+            description="Use GPU acceleration"),
+
+    # ── Text processing ──────────────────────────────────────────
+    Setting("replace_single_newlines", bool, False,
+            description="Replace single newlines with spaces"),
+    Setting("max_subtitle_words", int, 50, min_value=1, max_value=500,
+            description="Max words per subtitle"),
+    Setting("enable_entity_recognition", bool, True,
+            description="Enable entity recognition"),
+
+    # ── Speaker analysis ─────────────────────────────────────────
+    Setting("speaker_analysis_threshold", int, 3, min_value=1, max_value=25,
+            description="Speaker analysis threshold"),
+    Setting("speaker_pronunciation_sentence", str, "This is {{name}} speaking.",
+            description="Template for pronunciation samples"),
+    Setting("speaker_random_languages", list, [],
+            normalizer=_norm_language_list,
+            description="Languages for random speaker assignment"),
+
+    # ── LLM ──────────────────────────────────────────────────────
+    Setting("llm_base_url", str, lambda: _default_llm("llm_base_url"),
+            normalizer=_norm_stripped_str,
+            description="LLM API base URL"),
+    Setting("llm_api_key", str, lambda: _default_llm("llm_api_key"),
+            normalizer=_norm_stripped_str,
+            description="LLM API key"),
+    Setting("llm_model", str, lambda: _default_llm("llm_model"),
+            normalizer=_norm_stripped_str,
+            description="LLM model name"),
+    Setting("llm_timeout", float, lambda: _default_llm("llm_timeout") or 30.0,
+            min_value=1.0,
+            description="LLM request timeout"),
+    Setting("llm_prompt", str, lambda: _default_llm("llm_prompt") or DEFAULT_LLM_PROMPT,
+            normalizer=_norm_prompt,
+            description="LLM normalization prompt"),
+    Setting("llm_context_mode", str, lambda: _default_llm("llm_context_mode") or "sentence",
+            valid_values=("sentence",),
+            description="LLM context mode"),
+
+    # ── Normalization (booleans) ─────────────────────────────────
+    Setting("normalization_numbers", bool, True,
+            description="Convert grouped numbers to words"),
+    Setting("normalization_currency", bool, True,
+            description="Convert currency symbols"),
+    Setting("normalization_footnotes", bool, True,
+            description="Remove footnote indicators"),
+    Setting("normalization_titles", bool, True,
+            description="Expand titles and suffixes"),
+    Setting("normalization_terminal", bool, True,
+            description="Ensure terminal punctuation"),
+    Setting("normalization_phoneme_hints", bool, True,
+            description="Add phoneme hints for possessives"),
+    Setting("normalization_caps_quotes", bool, True,
+            description="Convert ALL CAPS in quotes"),
+    Setting("normalization_internet_slang", bool, False,
+            description="Expand internet slang"),
+    Setting("normalization_apostrophes_contractions", bool, True,
+            description="Expand contractions"),
+    Setting("normalization_apostrophes_plural_possessives", bool, True,
+            description="Collapse plural possessives"),
+    Setting("normalization_apostrophes_sibilant_possessives", bool, True,
+            description="Mark sibilant possessives"),
+    Setting("normalization_apostrophes_decades", bool, True,
+            description="Expand decades"),
+    Setting("normalization_apostrophes_leading_elisions", bool, True,
+            description="Expand leading elisions"),
+    Setting("normalization_contraction_aux_be", bool, True,
+            description="Expand auxiliary 'be'"),
+    Setting("normalization_contraction_aux_have", bool, True,
+            description="Expand auxiliary 'have'"),
+    Setting("normalization_contraction_modal_will", bool, True,
+            description="Expand modal 'will'"),
+    Setting("normalization_contraction_modal_would", bool, True,
+            description="Expand modal 'would'"),
+    Setting("normalization_contraction_negation_not", bool, True,
+            description="Expand negation 'not'"),
+    Setting("normalization_contraction_let_us", bool, True,
+            description="Expand 'let's'"),
+
+    # ── Normalization (strings) ──────────────────────────────────
+    Setting("normalization_apostrophe_mode", str, "spacy",
+            valid_values=("off", "spacy", "llm"),
+            description="Apostrophe handling mode"),
+    Setting("normalization_numbers_year_style", str, "american",
+            valid_values=("american", "off"),
+            description="Year style for number normalization"),
+
+    # ── PyQt GUI-only ────────────────────────────────────────────
+    Setting("theme", str, "system",
+            gui_only=True,
+            description="UI theme"),
+    Setting("check_updates", bool, True,
+            gui_only=True,
+            description="Check for updates on startup"),
+    Setting("subtitle_mode", str, "Sentence",
+            gui_only=True,
+            description="Subtitle display mode"),
+    Setting("selected_format", str, "wav",
+            gui_only=True,
+            description="Last selected audio format"),
+    Setting("selected_voice", str, "af_heart",
+            gui_only=True,
+            description="Last selected voice"),
+    Setting("selected_profile_name", str, None,
+            gui_only=True,
+            description="Last selected profile name"),
+    Setting("log_window_max_lines", int, 2000, min_value=100,
+            gui_only=True,
+            description="Max lines in log window"),
+    Setting("use_silent_gaps", bool, True,
+            gui_only=True,
+            description="Use silent gaps between chunks"),
+    Setting("subtitle_speed_method", str, "tts",
+            gui_only=True,
+            valid_values=("tts", "ffmpeg"),
+            description="Speed adjustment method for subtitles"),
+    Setting("use_spacy_segmentation", bool, True,
+            gui_only=True,
+            description="Use spaCy for sentence segmentation"),
+    Setting("word_substitutions_enabled", bool, False,
+            gui_only=True,
+            description="Enable word substitutions"),
+    Setting("word_substitutions_list", str, "",
+            gui_only=True,
+            description="Word substitutions list"),
+    Setting("case_sensitive_substitutions", bool, False,
+            gui_only=True,
+            description="Case-sensitive substitutions"),
+    Setting("replace_all_caps", bool, False,
+            gui_only=True,
+            description="Replace ALL CAPS text"),
+    Setting("replace_numerals", bool, False,
+            gui_only=True,
+            description="Replace numerals with words"),
+    Setting("fix_nonstandard_punctuation", bool, False,
+            gui_only=True,
+            description="Fix nonstandard punctuation"),
+    Setting("queue_override_settings", bool, False,
+            gui_only=True,
+            description="Override settings per queue item"),
+    Setting("disable_kokoro_internet", bool, False,
+            description="Disable Kokoro internet access"),
+]
+
+
+# ── Registry helpers ─────────────────────────────────────────────────
+
+_REGISTRY_BY_KEY: dict[str, Setting] = {s.key: s for s in SETTINGS_REGISTRY}
+
+SETTING_KEYS: frozenset[str] = frozenset(_REGISTRY_BY_KEY.keys())
+GUI_ONLY_KEYS: frozenset[str] = frozenset(s.key for s in SETTINGS_REGISTRY if s.gui_only)
+WEB_ONLY_KEYS: frozenset[str] = frozenset(s.key for s in SETTINGS_REGISTRY if s.web_only)
+SHARED_KEYS: frozenset[str] = SETTING_KEYS - GUI_ONLY_KEYS - WEB_ONLY_KEYS
+
+BOOLEAN_SETTINGS: frozenset[str] = frozenset(s.key for s in SETTINGS_REGISTRY if s.type_ is bool)
+FLOAT_SETTINGS: frozenset[str] = frozenset(s.key for s in SETTINGS_REGISTRY if s.type_ is float)
+INT_SETTINGS: frozenset[str] = frozenset(s.key for s in SETTINGS_REGISTRY if s.type_ is int)
+
+# Backward-compatible aliases (used by existing code)
+_NORMALIZATION_BOOLEAN_KEYS: frozenset[str] = frozenset(
+    s.key for s in SETTINGS_REGISTRY
+    if s.type_ is bool and s.key.startswith("normalization_")
+)
+_NORMALIZATION_STRING_KEYS: frozenset[str] = frozenset(
+    s.key for s in SETTINGS_REGISTRY
+    if s.type_ is str and s.key.startswith("normalization_")
+)
+
+
+def get_setting(key: str) -> Setting | None:
+    """Look up a setting by key."""
+    return _REGISTRY_BY_KEY.get(key)
+
+
+def has_output_override() -> bool:
+    return bool(os.environ.get("ABOGEN_OUTPUT_DIR") or os.environ.get("ABOGEN_OUTPUT_ROOT"))
+
+
+# ── Defaults ─────────────────────────────────────────────────────────
+
+def settings_defaults() -> Dict[str, Any]:
+    """Default values for all shared settings (excludes gui_only)."""
+    result: Dict[str, Any] = {}
+    for s in SETTINGS_REGISTRY:
+        if s.gui_only:
+            continue
+        result[s.key] = s.default() if callable(s.default) else s.default
+    return result
+
+
+def all_settings_defaults() -> Dict[str, Any]:
+    """Default values for ALL settings (including gui_only)."""
+    result: Dict[str, Any] = {}
+    for s in SETTINGS_REGISTRY:
+        result[s.key] = s.default() if callable(s.default) else s.default
+    return result
+
+
+def load_settings() -> Dict[str, Any]:
+    """Load and normalize settings from config file."""
+    from abogen.utils import load_config
+    defaults = settings_defaults()
+    cfg = load_config() or {}
+    settings: Dict[str, Any] = {}
+    for key, default in defaults.items():
+        raw_value = cfg.get(key, default)
+        settings[key] = normalize_setting_value(key, raw_value, defaults)
+    return settings
+
+
+# ── Normalization (delegates to Setting.coerce) ──────────────────────
+
+def normalize_setting_value(key: str, value: Any, defaults: Dict[str, Any]) -> Any:
+    """Normalize a single setting value using the registry schema."""
+    setting = _REGISTRY_BY_KEY.get(key)
+    if setting is None:
+        return value if value is not None else defaults.get(key)
+
+    fallback = defaults.get(key, setting.default() if callable(setting.default) else setting.default)
+
+    if setting.normalizer is not None:
+        return setting.normalizer(value, fallback)
+
+    return setting.coerce(value, fallback)
+
+
+def validate_setting(key: str, value: Any) -> tuple[bool, str]:
+    """Validate a setting value against its schema. Returns (ok, error_message)."""
+    setting = _REGISTRY_BY_KEY.get(key)
+    if setting is None:
+        return False, f"Unknown setting: {key}"
+    if setting.type_ is str and setting.valid_values is not None:
+        v = str(value or "").strip()
+        if v and v not in setting.valid_values:
+            return False, f"Invalid value '{v}' for {key}. Allowed: {setting.valid_values}"
+    if setting.type_ is int:
+        try:
+            iv = int(value)
+        except (TypeError, ValueError):
+            return False, f"Invalid integer value for {key}: {value!r}"
+        if setting.min_value is not None and iv < setting.min_value:
+            return False, f"{key} must be >= {setting.min_value}, got {iv}"
+        if setting.max_value is not None and iv > setting.max_value:
+            return False, f"{key} must be <= {setting.max_value}, got {iv}"
+    if setting.type_ is float:
+        try:
+            fv = float(value)
+        except (TypeError, ValueError):
+            return False, f"Invalid float value for {key}: {value!r}"
+        if setting.min_value is not None and fv < setting.min_value:
+            return False, f"{key} must be >= {setting.min_value}, got {fv}"
+        if setting.max_value is not None and fv > setting.max_value:
+            return False, f"{key} must be <= {setting.max_value}, got {fv}"
+    return True, ""
+
+
+# ── Constants (backward-compatible) ──────────────────────────────────
+
+SAVE_MODE_LABELS = {
+    "save_next_to_input": "Save next to input file",
+    "save_to_desktop": "Save to Desktop",
+    "choose_output_folder": "Choose output folder",
+    "default_output": "Use default save location",
+}
+
+LEGACY_SAVE_MODE_MAP = {label: key for key, label in SAVE_MODE_LABELS.items()}
+
+CHUNK_LEVEL_OPTIONS = [
+    {"value": "paragraph", "label": "Paragraphs"},
+    {"value": "sentence", "label": "Sentences"},
+]
+
+CHUNK_LEVEL_VALUES = frozenset(option["value"] for option in CHUNK_LEVEL_OPTIONS)
+
+DEFAULT_ANALYSIS_THRESHOLD = 3
+
+
+# ── Coercion helpers (backward-compatible, delegate to Setting.coerce) ──
+
+def coerce_bool(value: Any, default: bool) -> bool:
+    return Setting("_", bool, default).coerce(value, default)
+
+
+def coerce_float(value: Any, default: float) -> float:
+    return Setting("_", float, default).coerce(value, default)
+
+
+def coerce_int(value: Any, default: int, *, minimum: int = 1, maximum: int = 200) -> int:
+    return Setting("_", int, default, min_value=minimum, max_value=maximum).coerce(value, default)
+
+
+def split_profile_spec(value: Any) -> tuple[str, str | None]:
+    """Split 'speaker:Name' or 'profile:Name' into (raw, name)."""
+    text = str(value or "").strip()
+    if not text:
+        return "", None
+    lowered = text.lower()
+    if lowered.startswith("profile:") or lowered.startswith("speaker:"):
+        _, _, remainder = text.partition(":")
+        name = remainder.strip()
+        return "", name or None
+    return text, None
+
+
+def normalize_save_mode(value: Any, default: str) -> str:
+    return _norm_save_mode(value, default)
+
+
+# ── LLM helpers ──────────────────────────────────────────────────────
+
+_PROMPT_TOKEN_RE = re.compile(r"{{\s*([a-zA-Z0-9_]+)\s*}}")
+
+
+def llm_ready(settings: Mapping[str, Any]) -> bool:
+    base_url = str(settings.get("llm_base_url") or "").strip()
+    return bool(base_url)
+
+
+def render_prompt_template(template: str, context: Mapping[str, str]) -> str:
+    if not template:
+        return ""
+
+    def _replace(match: re.Match[str]) -> str:
+        key = match.group(1)
+        return context.get(key, "")
+
+    return _PROMPT_TOKEN_RE.sub(_replace, template)
+
+
+# ── Integration defaults ─────────────────────────────────────────────
+
+def integration_defaults() -> Dict[str, Dict[str, Any]]:
+    """Default values for integration settings."""
+    return {
+        "calibre_opds": {
+            "enabled": False,
+            "base_url": "",
+            "username": "",
+            "password": "",
+            "verify_ssl": True,
+        },
+        "audiobookshelf": {
+            "enabled": False,
+            "base_url": "",
+            "api_token": "",
+            "library_id": "",
+            "collection_id": "",
+            "folder_id": "",
+            "verify_ssl": True,
+            "send_cover": True,
+            "send_chapters": True,
+            "send_subtitles": False,
+            "auto_send": False,
+            "timeout": 30.0,
+        },
+    }
+
+
+def stored_integration_config(name: str) -> Dict[str, Any]:
+    """Read raw integration config from config.json.
+
+    Reads ``config["integrations"][name]``.
+    """
+    from abogen.utils import load_config
+
+    cfg = load_config() or {}
+    integrations = cfg.get("integrations")
+    if isinstance(integrations, Mapping):
+        entry = integrations.get(name)
+        if isinstance(entry, Mapping):
+            return dict(entry)
+    return {}
+
+
+def load_audiobookshelf_config() -> Optional["AudiobookshelfConfig"]:
+    """Read Audiobookshelf settings from config.json and build typed config.
+
+    Returns ``None`` when the integration is not configured or required
+    fields are missing.
+    """
+    raw = stored_integration_config("audiobookshelf")
+    if not raw:
+        return None
+    return build_audiobookshelf_config(raw)
+
+
+def build_audiobookshelf_config(
+    settings: Mapping[str, Any],
+) -> Optional["AudiobookshelfConfig"]:
+    """Build :class:`AudiobookshelfConfig` from a settings dict.
+
+    Returns ``None`` when required fields (base_url, api_token, library_id)
+    are missing.
+    """
+    from abogen.integrations.audiobookshelf import AudiobookshelfConfig
+
+    base_url = str(settings.get("base_url") or "").strip()
+    api_token = str(settings.get("api_token") or "").strip()
+    library_id = str(settings.get("library_id") or "").strip()
+    if not (base_url and api_token and library_id):
+        return None
+    try:
+        timeout = float(settings.get("timeout", 3600.0))
+    except (TypeError, ValueError):
+        timeout = 3600.0
+    return AudiobookshelfConfig(
+        base_url=base_url,
+        api_token=api_token,
+        library_id=library_id,
+        collection_id=(str(settings.get("collection_id") or "").strip() or None),
+        folder_id=(str(settings.get("folder_id") or "").strip() or None),
+        verify_ssl=coerce_bool(settings.get("verify_ssl"), True),
+        send_cover=coerce_bool(settings.get("send_cover"), True),
+        send_chapters=coerce_bool(settings.get("send_chapters"), True),
+        send_subtitles=coerce_bool(settings.get("send_subtitles"), False),
+        timeout=timeout,
+    )

abogen/domain/speaker_metadata.py

@@ -0,0 +1,381 @@
+"""Speaker metadata functions for building and applying speaker rosters.
+
+This module contains the core logic for:
+- Building narrator and speaker rosters from analysis results
+- Matching speakers to configured presets
+- Applying speaker config presets to rosters
+- Preparing full speaker metadata for conversion
+
+Moved from webui/routes/utils/voice.py to be available across all UIs.
+"""
+
+from typing import Any, Dict, Iterable, List, Mapping, Optional, Tuple, cast
+
+from abogen.speaker_analysis import analyze_speakers
+from abogen.speaker_configs import slugify_label
+from abogen.domain.settings_core import load_settings
+
+
+def build_narrator_roster(
+    voice: str,
+    voice_profile: Optional[str],
+    existing: Optional[Mapping[str, Any]] = None,
+) -> Dict[str, Any]:
+    roster: Dict[str, Any] = {
+        "narrator": {
+            "id": "narrator",
+            "label": "Narrator",
+            "voice": voice,
+        }
+    }
+    if voice_profile:
+        roster["narrator"]["voice_profile"] = voice_profile
+    existing_entry: Optional[Mapping[str, Any]] = None
+    if existing is not None:
+        existing_entry = existing.get("narrator") if isinstance(existing, Mapping) else None
+    if isinstance(existing_entry, Mapping):
+        roster_entry = roster["narrator"]
+        for key in ("label", "voice", "voice_profile", "voice_formula", "pronunciation"):
+            value = existing_entry.get(key)
+            if value is not None and value != "":
+                roster_entry[key] = value
+    return roster
+
+
+def build_speaker_roster(
+    analysis: Dict[str, Any],
+    base_voice: str,
+    voice_profile: Optional[str],
+    existing: Optional[Mapping[str, Any]] = None,
+    order: Optional[Iterable[str]] = None,
+) -> Dict[str, Any]:
+    roster = build_narrator_roster(base_voice, voice_profile, existing)
+    existing_map: Dict[str, Any] = dict(existing) if isinstance(existing, Mapping) else {}
+    speakers = analysis.get("speakers", {}) if isinstance(analysis, dict) else {}
+    ordered_ids: Iterable[str]
+    if order is not None:
+        ordered_ids = [sid for sid in order if sid in speakers]
+    else:
+        ordered_ids = speakers.keys()
+
+    for speaker_id in ordered_ids:
+        payload = speakers.get(speaker_id, {})
+        if speaker_id == "narrator":
+            continue
+        if isinstance(payload, Mapping) and payload.get("suppressed"):
+            continue
+        previous = existing_map.get(speaker_id)
+        roster[speaker_id] = {
+            "id": speaker_id,
+            "label": payload.get("label") or speaker_id.replace("_", " ").title(),
+            "analysis_confidence": payload.get("confidence"),
+            "analysis_count": payload.get("count"),
+            "gender": payload.get("gender", "unknown"),
+        }
+        detected_gender = payload.get("detected_gender")
+        if detected_gender:
+            roster[speaker_id]["detected_gender"] = detected_gender
+        samples = payload.get("sample_quotes")
+        if isinstance(samples, list):
+            roster[speaker_id]["sample_quotes"] = samples
+        if isinstance(previous, Mapping):
+            for key in ("voice", "voice_profile", "voice_formula", "resolved_voice", "pronunciation"):
+                value = previous.get(key)
+                if value is not None and value != "":
+                    roster[speaker_id][key] = value
+            if "sample_quotes" not in roster[speaker_id]:
+                prev_samples = previous.get("sample_quotes")
+                if isinstance(prev_samples, list):
+                    roster[speaker_id]["sample_quotes"] = prev_samples
+            if "detected_gender" not in roster[speaker_id]:
+                prev_detected = previous.get("detected_gender")
+                if isinstance(prev_detected, str) and prev_detected:
+                    roster[speaker_id]["detected_gender"] = prev_detected
+    return roster
+
+
+def match_configured_speaker(
+    config_speakers: Mapping[str, Any],
+    roster_id: str,
+    roster_label: str,
+) -> Optional[Mapping[str, Any]]:
+    if not config_speakers:
+        return None
+    entry = config_speakers.get(roster_id)
+    if entry:
+        return cast(Mapping[str, Any], entry)
+    slug = slugify_label(roster_label)
+    if slug != roster_id and slug in config_speakers:
+        return cast(Mapping[str, Any], config_speakers[slug])
+    lower_label = roster_label.strip().lower()
+    for record in config_speakers.values():
+        if not isinstance(record, Mapping):
+            continue
+        if str(record.get("label", "")).strip().lower() == lower_label:
+            return record
+    return None
+
+
+def apply_speaker_config_to_roster(
+    roster: Mapping[str, Any],
+    config: Optional[Mapping[str, Any]],
+    *,
+    persist_changes: bool = False,
+    fallback_languages: Optional[Iterable[str]] = None,
+) -> Tuple[Dict[str, Any], List[str], Optional[Dict[str, Any]]]:
+    if not isinstance(roster, Mapping):
+        effective_languages = [code for code in (fallback_languages or []) if isinstance(code, str) and code]
+        return {}, effective_languages, None
+    updated_roster: Dict[str, Any] = {key: dict(value) for key, value in roster.items() if isinstance(value, Mapping)}
+    if not config:
+        effective_languages = [code for code in (fallback_languages or []) if isinstance(code, str) and code]
+        return updated_roster, effective_languages, None
+
+    speakers_map = config.get("speakers")
+    if not isinstance(speakers_map, Mapping):
+        effective_languages = [code for code in (fallback_languages or []) if isinstance(code, str) and code]
+        return updated_roster, effective_languages, None
+
+    config_languages = config.get("languages")
+    if isinstance(config_languages, list):
+        allowed_languages = [code for code in config_languages if isinstance(code, str) and code]
+    else:
+        allowed_languages = []
+    if not allowed_languages and fallback_languages:
+        allowed_languages = [code for code in fallback_languages if isinstance(code, str) and code]
+
+    default_voice = config.get("default_voice") if isinstance(config.get("default_voice"), str) else ""
+    used_voices = {entry.get("resolved_voice") or entry.get("voice") for entry in updated_roster.values()} - {None}
+    narrator_voice = ""
+    narrator_entry = updated_roster.get("narrator") if isinstance(updated_roster, Mapping) else None
+    if isinstance(narrator_entry, Mapping):
+        narrator_voice = str(
+            narrator_entry.get("resolved_voice")
+            or narrator_entry.get("default_voice")
+            or ""
+        ).strip()
+        if narrator_voice:
+            used_voices.add(narrator_voice)
+
+    config_changed = False
+    new_config_payload: Dict[str, Any] = {
+        "language": config.get("language", "a"),
+        "languages": allowed_languages,
+        "default_voice": default_voice,
+        "speakers": dict(speakers_map),
+        "version": config.get("version", 1),
+        "notes": config.get("notes", ""),
+    }
+
+    speakers_payload = new_config_payload["speakers"]
+
+    for speaker_id, roster_entry in updated_roster.items():
+        if speaker_id == "narrator":
+            continue
+        label = str(roster_entry.get("label") or speaker_id)
+        config_entry = match_configured_speaker(speakers_map, speaker_id, label)
+        if config_entry is None:
+            continue
+        voice_id = str(config_entry.get("voice") or "").strip()
+        voice_profile = str(config_entry.get("voice_profile") or "").strip()
+        voice_formula = str(config_entry.get("voice_formula") or "").strip()
+        resolved_voice = str(config_entry.get("resolved_voice") or "").strip()
+        languages = config_entry.get("languages") if isinstance(config_entry.get("languages"), list) else []
+        chosen_voice = resolved_voice or voice_formula or voice_id or roster_entry.get("voice")
+        usable_languages = languages or allowed_languages
+
+        if chosen_voice:
+            roster_entry["resolved_voice"] = chosen_voice
+            roster_entry["voice"] = chosen_voice if not voice_profile and not voice_formula else roster_entry.get("voice", chosen_voice)
+        if voice_profile:
+            roster_entry["voice_profile"] = voice_profile
+        if voice_formula:
+            roster_entry["voice_formula"] = voice_formula
+            roster_entry["resolved_voice"] = voice_formula
+        if not voice_formula and not voice_profile and resolved_voice:
+            roster_entry["resolved_voice"] = resolved_voice
+        roster_entry["config_languages"] = usable_languages or []
+
+        if chosen_voice:
+            used_voices.add(chosen_voice)
+
+        # persist updates back to config payload if required
+        if persist_changes:
+            slug = config_entry.get("id") or slugify_label(label)
+            speakers_payload[slug] = {
+                "id": slug,
+                "label": label,
+                "gender": config_entry.get("gender", "unknown"),
+                "voice": voice_id,
+                "voice_profile": voice_profile,
+                "voice_formula": voice_formula,
+                "resolved_voice": roster_entry.get("resolved_voice", resolved_voice or voice_id),
+                "languages": usable_languages,
+            }
+
+    new_config = new_config_payload if (persist_changes and config_changed) else None
+    return updated_roster, allowed_languages, new_config
+
+
+def prepare_speaker_metadata(
+    *,
+    chapters: List[Dict[str, Any]],
+    chunks: List[Dict[str, Any]],
+    analysis_chunks: Optional[List[Dict[str, Any]]] = None,
+    voice: str,
+    voice_profile: Optional[str],
+    threshold: int,
+    existing_roster: Optional[Mapping[str, Any]] = None,
+    run_analysis: bool = True,
+    speaker_config: Optional[Mapping[str, Any]] = None,
+    apply_config: bool = False,
+    persist_config: bool = False,
+    inject_recommended: Optional[Any] = None,
+) -> tuple[List[Dict[str, Any]], Dict[str, Any], Dict[str, Any], List[str], Optional[Dict[str, Any]]]:
+    chunk_list = [dict(chunk) for chunk in chunks]
+    analysis_source = [dict(chunk) for chunk in (analysis_chunks or chunks)]
+    threshold_value = max(1, int(threshold))
+    analysis_enabled = run_analysis
+    settings_state = load_settings()
+    global_random_languages = [
+        code
+        for code in settings_state.get("speaker_random_languages", [])
+        if isinstance(code, str) and code
+    ]
+
+    if not analysis_enabled:
+        for chunk in chunk_list:
+            chunk["speaker_id"] = "narrator"
+            chunk["speaker_label"] = "Narrator"
+        analysis_payload = {
+            "version": "1.0",
+            "narrator": "narrator",
+            "assignments": {str(chunk.get("id")): "narrator" for chunk in chunk_list},
+            "speakers": {
+                "narrator": {
+                    "id": "narrator",
+                    "label": "Narrator",
+                    "count": len(chunk_list),
+                    "confidence": "low",
+                    "sample_quotes": [],
+                    "suppressed": False,
+                }
+            },
+            "suppressed": [],
+            "stats": {
+                "total_chunks": len(chunk_list),
+                "explicit_chunks": 0,
+                "active_speakers": 0,
+                "unique_speakers": 1,
+                "suppressed": 0,
+            },
+        }
+        roster = build_narrator_roster(voice, voice_profile, existing_roster)
+        narrator_pron = roster["narrator"].get("pronunciation")
+        if narrator_pron:
+            analysis_payload["speakers"]["narrator"]["pronunciation"] = narrator_pron
+        return chunk_list, roster, analysis_payload, [], None
+
+    analysis_result = analyze_speakers(
+        chapters,
+        analysis_source,
+        threshold=threshold_value,
+        max_speakers=0,
+    )
+    analysis_payload = analysis_result.to_dict()
+    speakers_payload = analysis_payload.get("speakers", {})
+    ordered_ids = [
+        sid
+        for sid, meta in sorted(
+            (
+                (sid, meta)
+                for sid, meta in speakers_payload.items()
+                if sid != "narrator" and isinstance(meta, Mapping) and not meta.get("suppressed")
+            ),
+            key=lambda item: item[1].get("count", 0),
+            reverse=True,
+        )
+    ]
+    analysis_payload["ordered_speakers"] = ordered_ids
+    assignments = analysis_payload.get("assignments", {})
+    suppressed_ids = analysis_payload.get("suppressed", [])
+    suppressed_details: List[Dict[str, Any]] = []
+    speakers_payload = analysis_payload.get("speakers", {})
+    if isinstance(suppressed_ids, Iterable):
+        for suppressed_id in suppressed_ids:
+            speaker_meta = speakers_payload.get(suppressed_id) if isinstance(speakers_payload, dict) else None
+            if isinstance(speaker_meta, dict):
+                suppressed_details.append(
+                    {
+                        "id": suppressed_id,
+                        "label": speaker_meta.get("label")
+                        or str(suppressed_id).replace("_", " ").title(),
+                        "pronunciation": speaker_meta.get("pronunciation"),
+                    }
+                )
+            else:
+                suppressed_details.append(
+                    {
+                        "id": suppressed_id,
+                        "label": str(suppressed_id).replace("_", " ").title(),
+                        "pronunciation": None,
+                    }
+                )
+    analysis_payload["suppressed_details"] = suppressed_details
+    roster = build_speaker_roster(
+        analysis_payload,
+        voice,
+        voice_profile,
+        existing=existing_roster,
+        order=analysis_payload.get("ordered_speakers"),
+    )
+    applied_languages: List[str] = []
+    updated_config: Optional[Dict[str, Any]] = None
+    if apply_config and speaker_config:
+        roster, applied_languages, updated_config = apply_speaker_config_to_roster(
+            roster,
+            speaker_config,
+            persist_changes=persist_config,
+            fallback_languages=global_random_languages,
+        )
+        speakers_payload = analysis_payload.get("speakers")
+        if isinstance(speakers_payload, dict):
+            for roster_id, roster_payload in roster.items():
+                speaker_meta = speakers_payload.get(roster_id)
+                if isinstance(speaker_meta, dict):
+                    for key in ("voice", "voice_profile", "voice_formula", "resolved_voice"):
+                        value = roster_payload.get(key)
+                        if value:
+                            speaker_meta[key] = value
+    effective_languages: List[str] = []
+    if applied_languages:
+        effective_languages = applied_languages
+    elif isinstance(analysis_payload.get("config_languages"), list):
+        effective_languages = [
+            code for code in analysis_payload.get("config_languages", []) if isinstance(code, str) and code
+        ]
+    elif global_random_languages:
+        effective_languages = list(global_random_languages)
+
+    if effective_languages:
+        analysis_payload["config_languages"] = effective_languages
+    speakers_payload = analysis_payload.get("speakers")
+    if isinstance(speakers_payload, dict):
+        for roster_id, roster_payload in roster.items():
+            if roster_id in speakers_payload and isinstance(roster_payload, dict):
+                pronunciation_value = roster_payload.get("pronunciation")
+                if pronunciation_value:
+                    speakers_payload[roster_id]["pronunciation"] = pronunciation_value
+
+    fallback_languages = effective_languages or []
+    if callable(inject_recommended):
+        inject_recommended(roster, fallback_languages=fallback_languages)
+
+    for chunk in chunk_list:
+        chunk_id = str(chunk.get("id"))
+        speaker_id = assignments.get(chunk_id, "narrator")
+        chunk["speaker_id"] = speaker_id
+        speaker_meta = roster.get(speaker_id)
+        chunk["speaker_label"] = speaker_meta.get("label") if isinstance(speaker_meta, dict) else speaker_id
+
+    return chunk_list, roster, analysis_payload, applied_languages, updated_config

abogen/domain/split_pattern.py

@@ -0,0 +1,49 @@
+from __future__ import annotations
+
+"""Unified split pattern logic extracted from 3 copies."""
+
+from abogen.domain.enums import Language, SubtitleMode
+
+# Canonical punctuation sets covering all supported scripts:
+# ASCII (. ! ?), Arabic ؟, CJK (。！？), Devanagari ।
+PUNCTUATION_SENTENCE = r".!?؟。！？।"
+# Commas: ASCII , CJK fullwidth ，CJK ideographic 、
+PUNCTUATION_SENTENCE_COMMA = r".!?,？。！？،，、।"
+PUNCTUATION_COMMAS = ",，、"
+
+
+def get_split_pattern(language: Language, subtitle_mode: str) -> str:
+    """Get the appropriate split pattern based on language and subtitle mode.
+
+    Args:
+        language: Language enum value.
+        subtitle_mode: Subtitle mode ("Sentence", "Sentence + Comma", "Line", etc.)
+
+    Returns:
+        Split pattern string
+    """
+    try:
+        mode = SubtitleMode.from_str(subtitle_mode) if not isinstance(subtitle_mode, SubtitleMode) else subtitle_mode
+    except ValueError:
+        mode = SubtitleMode.DISABLED
+
+    # For English, always use newline splitting only
+    if language in (Language.EN_US, Language.EN_GB):
+        return "\n"
+
+    # Determine spacing pattern based on language
+    spacing = r"\s*" if language.is_cjk else r"\s+"
+
+    # For CJK languages, when subtitle mode is Disabled or Line, prefer
+    # punctuation-based splitting instead of plain newline splitting.
+    if mode in (SubtitleMode.DISABLED, SubtitleMode.LINE) and language.is_cjk:
+        return rf"(?<=[{PUNCTUATION_SENTENCE}]){spacing}|\n+"
+
+    if mode == SubtitleMode.LINE:
+        return "\n"
+    elif mode == SubtitleMode.SENTENCE:
+        return rf"(?<=[{PUNCTUATION_SENTENCE}]){spacing}|\n+"
+    elif mode == SubtitleMode.SENTENCE_COMMA:
+        return rf"(?<=[{PUNCTUATION_SENTENCE_COMMA}]){spacing}|\n+"
+    else:
+        return r"\n+"

abogen/domain/subtitle_generation.py

@@ -0,0 +1,366 @@
+"""Subtitle generation utilities for audiobook generation.
+
+This module provides functions for processing TTS tokens into subtitle entries
+according to various subtitle modes (Line, Sentence, Sentence + Comma,
+Sentence + Highlighting).
+"""
+
+from __future__ import annotations
+
+import re
+from typing import List, Optional, Tuple
+
+from abogen.domain.enums import Language, SubtitleMode
+from abogen.domain.split_pattern import PUNCTUATION_SENTENCE, PUNCTUATION_SENTENCE_COMMA
+
+
+def process_subtitle_tokens(
+    tokens_with_timestamps: List[dict],
+    subtitle_entries: List[Tuple[float, float, str]],
+    max_subtitle_words: int,
+    subtitle_mode: str,
+    language: Language,
+    use_spacy_segmentation: bool = False,
+    fallback_end_time: Optional[float] = None,
+) -> None:
+    """Process TTS tokens into subtitle entries according to the subtitle mode.
+    
+    This function modifies subtitle_entries in-place by appending new entries.
+    
+    Args:
+        tokens_with_timestamps: List of token dictionaries with 'start', 'end', 'text',
+            and 'whitespace' keys.
+        subtitle_entries: List to append subtitle entries to (modified in-place).
+            Each entry is a tuple of (start_time, end_time, text).
+        max_subtitle_words: Maximum number of words per subtitle entry.
+        subtitle_mode: One of "Disabled", "Line", "Sentence", "Sentence + Comma",
+            "Sentence + Highlighting", or a string like "5" for word-count mode.
+        language: Language enum value for spaCy processing.
+        use_spacy_segmentation: Whether to use spaCy for sentence boundary detection.
+        fallback_end_time: Fallback end time for the last entry if none is available.
+    """
+    if not tokens_with_timestamps:
+        return
+
+    processed_tokens = tokens_with_timestamps
+
+    # For English with spaCy enabled and sentence-based modes, use spaCy for sentence boundaries
+    # spaCy is disabled when subtitle mode is "Disabled" or "Line"
+    use_spacy_for_english = (
+        use_spacy_segmentation
+        and subtitle_mode not in [SubtitleMode.DISABLED, SubtitleMode.LINE]
+        and language in [Language.EN_US, Language.EN_GB]
+        and subtitle_mode in [SubtitleMode.SENTENCE, SubtitleMode.SENTENCE_COMMA]
+    )
+
+    if subtitle_mode == SubtitleMode.SENTENCE_HIGHLIGHT:
+        _process_karaoke_highlighting(
+            processed_tokens, subtitle_entries, max_subtitle_words, fallback_end_time
+        )
+    elif subtitle_mode in [SubtitleMode.SENTENCE, SubtitleMode.SENTENCE_COMMA, SubtitleMode.LINE]:
+        if use_spacy_for_english and subtitle_mode != SubtitleMode.LINE:
+            _process_spacy_sentences(
+                processed_tokens, subtitle_entries, max_subtitle_words,
+                subtitle_mode, language, fallback_end_time
+            )
+        else:
+            _process_regex_sentences(
+                processed_tokens, subtitle_entries, max_subtitle_words,
+                subtitle_mode, fallback_end_time
+            )
+    else:
+        # Word count-based grouping (e.g., "5" for 5-word groups)
+        _process_word_count(
+            processed_tokens, subtitle_entries, max_subtitle_words,
+            subtitle_mode, fallback_end_time
+        )
+
+
+def _process_karaoke_highlighting(
+    tokens: List[dict],
+    subtitle_entries: List[Tuple[float, float, str]],
+    max_subtitle_words: int,
+    fallback_end_time: Optional[float],
+) -> None:
+    """Process tokens for Sentence + Highlighting mode (karaoke effect)."""
+    separator = rf"[{PUNCTUATION_SENTENCE}]"
+    current_sentence = []
+    word_count = 0
+
+    for token in tokens:
+        current_sentence.append(token)
+        word_count += 1
+
+        # Split sentences based on separator or word count
+        if (
+            re.search(separator, token["text"]) and token.get("whitespace") == " "
+        ) or word_count >= max_subtitle_words:
+            if current_sentence:
+                # Create karaoke subtitle entry for this sentence
+                start_time = current_sentence[0]["start"]
+                end_time = current_sentence[-1]["end"]
+
+                # Generate karaoke text with timing
+                karaoke_text = ""
+                for t in current_sentence:
+                    # Calculate duration in centiseconds
+                    duration = (
+                        t["end"] - t["start"]
+                        if t.get("end") is not None and t.get("start") is not None
+                        else 0.5
+                    )
+                    duration_cs = int(duration * 100)
+                    # Add karaoke effect
+                    karaoke_text += f"{{\\kf{duration_cs}}}{t['text']}{t.get('whitespace', '') or ''}"
+
+                subtitle_entries.append(
+                    (start_time, end_time, karaoke_text.strip())
+                )
+                current_sentence = []
+                word_count = 0
+
+    # Add any remaining tokens as a sentence
+    if current_sentence:
+        start_time = current_sentence[0]["start"]
+        end_time = current_sentence[-1]["end"]
+
+        # Generate karaoke text for remaining tokens
+        karaoke_text = ""
+        for t in current_sentence:
+            duration = t["end"] - t["start"] if t.get("end") and t.get("start") else 0.5
+            duration_cs = int(duration * 100)
+            karaoke_text += f"{{\\kf{duration_cs}}}{t['text']}{t.get('whitespace', '') or ''}"
+        subtitle_entries.append((start_time, end_time, karaoke_text.strip()))
+
+    # Fallback for last entry
+    _apply_fallback_end_time(subtitle_entries, fallback_end_time)
+
+
+def _process_spacy_sentences(
+    tokens: List[dict],
+    subtitle_entries: List[Tuple[float, float, str]],
+    max_subtitle_words: int,
+    subtitle_mode: str,
+    language: Language,
+    fallback_end_time: Optional[float],
+) -> None:
+    """Process tokens using spaCy for sentence boundary detection."""
+    try:
+        from abogen.spacy_utils import get_spacy_model
+    except ImportError:
+        # Fall back to regex if spaCy is not available
+        _process_regex_sentences(
+            tokens, subtitle_entries, max_subtitle_words,
+            subtitle_mode, fallback_end_time
+        )
+        return
+
+    nlp = get_spacy_model(language)
+    if not nlp:
+        _process_regex_sentences(
+            tokens, subtitle_entries, max_subtitle_words,
+            subtitle_mode, fallback_end_time
+        )
+        return
+
+    # Build full text and track character positions to token indices
+    full_text = ""
+    for token in tokens:
+        text_part = token["text"] + (token.get("whitespace") or "")
+        full_text += text_part
+
+    # Get sentence boundaries from spaCy
+    doc = nlp(full_text)
+    sentence_boundaries = [sent.end_char for sent in doc.sents]
+
+    # For "Sentence + Comma" mode, also split on commas
+    if subtitle_mode == SubtitleMode.SENTENCE_COMMA:
+        comma_positions = [
+            i + 1 for i, c in enumerate(full_text) if c == ","
+        ]
+        sentence_boundaries = sorted(
+            set(sentence_boundaries + comma_positions)
+        )
+
+    # Group tokens by sentence boundaries
+    current_sentence = []
+    word_count = 0
+    current_char_pos = 0
+    boundary_idx = 0
+
+    for token in tokens:
+        current_sentence.append(token)
+        word_count += 1
+        text_len = len(token["text"]) + len(token.get("whitespace") or "")
+        current_char_pos += text_len
+
+        # Check if we've hit a sentence boundary or max words
+        at_boundary = (
+            boundary_idx < len(sentence_boundaries)
+            and current_char_pos >= sentence_boundaries[boundary_idx]
+        )
+        if at_boundary or word_count >= max_subtitle_words:
+            if current_sentence:
+                start_time = current_sentence[0]["start"]
+                end_time = current_sentence[-1]["end"]
+                sentence_text = "".join(
+                    t["text"] + (t.get("whitespace") or "")
+                    for t in current_sentence
+                )
+                subtitle_entries.append(
+                    (start_time, end_time, sentence_text.strip())
+                )
+                current_sentence = []
+                word_count = 0
+            if at_boundary:
+                boundary_idx += 1
+
+    # Add remaining tokens
+    if current_sentence:
+        start_time = current_sentence[0]["start"]
+        end_time = current_sentence[-1]["end"]
+        sentence_text = "".join(
+            t["text"] + (t.get("whitespace") or "")
+            for t in current_sentence
+        )
+        subtitle_entries.append(
+            (start_time, end_time, sentence_text.strip())
+        )
+
+    # Fallback for last entry
+    _apply_fallback_end_time(subtitle_entries, fallback_end_time)
+
+
+def _process_regex_sentences(
+    tokens: List[dict],
+    subtitle_entries: List[Tuple[float, float, str]],
+    max_subtitle_words: int,
+    subtitle_mode: str,
+    fallback_end_time: Optional[float],
+) -> None:
+    """Process tokens using regex for sentence boundary detection."""
+    # Define separator pattern based on mode
+    if subtitle_mode == SubtitleMode.LINE:
+        separator = r"\n"
+    elif subtitle_mode == SubtitleMode.SENTENCE:
+        separator = rf"[{PUNCTUATION_SENTENCE}]"
+    else:  # Sentence + Comma
+        separator = rf"[{PUNCTUATION_SENTENCE_COMMA}]"
+
+    current_sentence = []
+    word_count = 0
+
+    for token in tokens:
+        current_sentence.append(token)
+        word_count += 1
+
+        # Split sentences based on separator or word count
+        if (
+            re.search(separator, token["text"]) and token.get("whitespace") == " "
+        ) or word_count >= max_subtitle_words:
+            if current_sentence:
+                # Create subtitle entry for this sentence
+                start_time = current_sentence[0]["start"]
+                end_time = current_sentence[-1]["end"]
+
+                # Simplified text joining logic
+                sentence_text = ""
+                for t in current_sentence:
+                    sentence_text += t["text"] + (t.get("whitespace") or "")
+
+                subtitle_entries.append(
+                    (start_time, end_time, sentence_text.strip())
+                )
+                current_sentence = []
+                word_count = 0
+
+    # Add any remaining tokens as a sentence (split multi-sentence FakeToken)
+    if current_sentence:
+        start_time = current_sentence[0]["start"]
+        end_time = current_sentence[-1]["end"]
+
+        sentence_text = ""
+        for t in current_sentence:
+            sentence_text += t["text"] + (t.get("whitespace") or "")
+        sentence_text = sentence_text.strip()
+
+        if len(current_sentence) == 1:
+            parts = re.split(rf"(?<={separator})\s+", sentence_text)
+            if len(parts) > 1:
+                d = end_time - start_time
+                for i, p in enumerate(parts):
+                    e = end_time if i == len(parts) - 1 else start_time + d * len(p) / len(sentence_text)
+                    subtitle_entries.append((start_time, e, p.strip()))
+                    start_time = e
+                current_sentence = []
+
+        if current_sentence:
+            subtitle_entries.append((start_time, end_time, sentence_text))
+
+    # Fallback for last entry
+    _apply_fallback_end_time(subtitle_entries, fallback_end_time)
+
+
+def _process_word_count(
+    tokens: List[dict],
+    subtitle_entries: List[Tuple[float, float, str]],
+    max_subtitle_words: int,
+    subtitle_mode: str,
+    fallback_end_time: Optional[float],
+) -> None:
+    """Process tokens by counting spaces (word count mode)."""
+    try:
+        word_count = int(subtitle_mode.split()[0])
+        word_count = min(word_count, max_subtitle_words)
+    except (ValueError, IndexError):
+        word_count = 1
+
+    current_group = []
+    space_count = 0
+
+    for token in tokens:
+        current_group.append(token)
+
+        # Count spaces after tokens (in the whitespace field)
+        if token.get("whitespace", "") == " ":
+            space_count += 1
+
+            # Split after counting N spaces
+            if space_count >= word_count:
+                text = "".join(
+                    t["text"] + (t.get("whitespace") or "")
+                    for t in current_group
+                )
+                subtitle_entries.append(
+                    (
+                        current_group[0]["start"],
+                        current_group[-1]["end"],
+                        text.strip(),
+                    )
+                )
+                current_group = []
+                space_count = 0
+
+    # Add any remaining tokens
+    if current_group:
+        text = "".join(
+            t["text"] + (t.get("whitespace") or "") for t in current_group
+        )
+        subtitle_entries.append(
+            (current_group[0]["start"], current_group[-1]["end"], text.strip())
+        )
+
+    # Fallback for last entry
+    _apply_fallback_end_time(subtitle_entries, fallback_end_time)
+
+
+def _apply_fallback_end_time(
+    subtitle_entries: List[Tuple[float, float, str]],
+    fallback_end_time: Optional[float],
+) -> None:
+    """Apply fallback end time to the last entry if needed."""
+    if subtitle_entries and fallback_end_time is not None:
+        last_entry = subtitle_entries[-1]
+        start, end, text = last_entry
+        if end is None or end <= start or end <= 0:
+            subtitle_entries[-1] = (start, fallback_end_time, text)

abogen/domain/subtitle_processor.py

@@ -0,0 +1,278 @@
+"""Subtitle-to-audio processing pipeline.
+
+Converts subtitle files (SRT/ASS/VTT/timestamp text) into audio by
+generating TTS for each entry and mixing into a buffer.
+"""
+
+from __future__ import annotations
+
+import logging
+import time
+from dataclasses import dataclass
+from typing import Any, Callable, List, Optional, Tuple
+
+import numpy as np
+
+from abogen.domain.audio_buffer import (
+    fit_audio_to_duration,
+    ffmpeg_time_stretch,
+    mix_audio,
+    normalize_audio,
+    SAMPLE_RATE,
+)
+from abogen.domain.audio_helpers import to_float32
+from abogen.domain.progress import calc_etr_str
+from abogen.subtitle_utils import (
+    parse_ass_file,
+    parse_srt_file,
+    parse_vtt_file,
+    parse_timestamp_text_file,
+)
+
+logger = logging.getLogger(__name__)
+
+
+@dataclass
+class SubtitleEntry:
+    """A single subtitle entry with timing."""
+    start: float
+    end: Optional[float]
+    text: str
+
+
+def parse_subtitle_file(
+    file_path: str,
+    is_timestamp_text: bool = False,
+) -> List[Tuple[float, Optional[float], str]]:
+    """Parse a subtitle file into (start, end, text) tuples.
+
+    Args:
+        file_path: Path to subtitle file.
+        is_timestamp_text: Whether to treat as timestamp text file.
+
+    Returns:
+        List of (start_time, end_time, text) tuples.
+    """
+    if is_timestamp_text:
+        return parse_timestamp_text_file(file_path)
+
+    import os
+    ext = os.path.splitext(file_path)[1].lower()
+    if ext == ".srt":
+        return parse_srt_file(file_path)
+    elif ext == ".vtt":
+        return parse_vtt_file(file_path)
+    else:
+        return parse_ass_file(file_path)
+
+
+def format_time_range(
+    start: float,
+    end: Optional[float],
+    is_auto_end: bool = False,
+) -> str:
+    """Format a time range for display in logs.
+
+    Args:
+        start: Start time in seconds.
+        end: End time in seconds, or None.
+        is_auto_end: Whether end time is auto-detected.
+
+    Returns:
+        Formatted string like "00:01:23,456 - 00:01:25,789" or "00:01:23 - AUTO".
+    """
+    def _fmt(seconds: float) -> str:
+        h = int(seconds // 3600)
+        m = int(seconds % 3600 // 60)
+        s = int(seconds % 60)
+        ms = int((seconds - int(seconds)) * 1000)
+        result = f"{h:02d}:{m:02d}:{s:02d}"
+        if ms > 0:
+            result += f",{ms:03d}"
+        return result
+
+    if is_auto_end or end is None:
+        return f"{_fmt(start)} - AUTO"
+    return f"{_fmt(start)} - {_fmt(end)}"
+
+
+def speed_up_audio(
+    audio: np.ndarray,
+    speed_factor: float,
+    method: str = "tts",
+    *,
+    backend: Any = None,
+    text: str = "",
+    voice: Any = None,
+    base_speed: float = 1.0,
+    sample_rate: int = SAMPLE_RATE,
+) -> np.ndarray:
+    """Speed up audio to fit a time window.
+
+    Args:
+        audio: Input audio buffer.
+        speed_factor: Required speed multiplier.
+        method: "ffmpeg" for time-stretch, "tts" for regeneration.
+        backend: TTS backend (required if method="tts").
+        text: Text to regenerate (required if method="tts").
+        voice: Voice to use for regeneration.
+        base_speed: Base speed for TTS.
+        sample_rate: Sample rate.
+
+    Returns:
+        Speed-adjusted audio buffer.
+    """
+    if speed_factor <= 1.0:
+        return audio
+
+    if method == "ffmpeg":
+        logger.info("FFmpeg time-stretch: %.2fx", speed_factor)
+        return ffmpeg_time_stretch(audio, speed_factor, sample_rate)
+
+    # TTS regeneration
+    if backend is None:
+        return audio
+    new_speed = base_speed * speed_factor
+    logger.info("Regenerating at %.2fx speed", new_speed)
+    results = [
+        r for r in backend(text, voice=voice, speed=new_speed, split_pattern=None)
+    ]
+    chunks = [r.audio for r in results]
+    if not chunks:
+        return audio
+    return np.concatenate([to_float32(c) for c in chunks])
+
+
+def process_subtitle_entries(
+    subtitles: List[Tuple[float, Optional[float], str]],
+    *,
+    backend: Any,
+    voice: Any,
+    speed: float = 1.0,
+    cancel_check: Callable[[], bool] = lambda: False,
+    log_callback: Optional[Callable[[str], None]] = None,
+    progress_callback: Optional[Callable[[int, str], None]] = None,
+    replace_newlines: bool = True,
+    use_gaps: bool = False,
+    is_timestamp_text: bool = False,
+    subtitle_speed_method: str = "tts",
+    sample_rate: int = SAMPLE_RATE,
+) -> np.ndarray:
+    """Process subtitle entries: generate TTS for each and mix into buffer.
+
+    This is the core domain logic for subtitle-to-audio conversion.
+    UI-specific concerns (signals, widgets) are handled via callbacks.
+
+    Args:
+        subtitles: List of (start, end, text) tuples.
+        backend: TTS pipeline callable.
+        voice: Resolved voice for TTS.
+        speed: TTS speed.
+        cancel_check: Returns True if processing should stop.
+        log_callback: Called with log messages.
+        progress_callback: Called with (percent, etr_string).
+        replace_newlines: Replace \\n with spaces in text.
+        use_gaps: Whether to use silent gaps between subtitles.
+        is_timestamp_text: Whether input is timestamp text.
+        subtitle_speed_method: "ffmpeg" or "tts" for speed adjustment.
+        sample_rate: Audio sample rate.
+
+    Returns:
+        Mixed audio buffer (float32).
+    """
+    if not subtitles:
+        return np.array([], dtype="float32")
+
+    max_end = max((end for _, end, _ in subtitles if end is not None), default=0)
+    buffer_samples = int(max_end * sample_rate) + sample_rate
+    audio_buffer = np.zeros(buffer_samples, dtype="float32")
+    etr_start = time.time()
+    total = len(subtitles)
+
+    for idx, (start_time, end_time, text) in enumerate(subtitles, 1):
+        if cancel_check():
+            break
+
+        processed_text = text.replace("\n", " ") if replace_newlines else text
+        next_start = (
+            subtitles[idx][0]
+            if (use_gaps and idx < total)
+            else float("inf")
+        )
+        subtitle_duration = None if end_time is None else end_time - start_time
+
+        is_auto_end = is_timestamp_text or (use_gaps and idx == total) or end_time is None
+        if log_callback:
+            log_callback(
+                f"\n[{idx}/{total}] {format_time_range(start_time, end_time, is_auto_end)}: {processed_text}"
+            )
+
+        # Generate TTS
+        results = [
+            r for r in backend(
+                processed_text, voice=voice, speed=speed, split_pattern=None
+            )
+            if not cancel_check()
+        ]
+        if cancel_check():
+            break
+
+        audio_chunks = [r.audio for r in results]
+        full_audio = (
+            np.concatenate([to_float32(a) for a in audio_chunks])
+            if audio_chunks
+            else np.zeros(int((subtitle_duration or 0) * sample_rate), dtype="float32")
+        )
+        audio_duration = len(full_audio) / sample_rate
+
+        # Timing adjustment
+        if is_timestamp_text:
+            end_time = start_time + audio_duration
+            subtitle_duration = audio_duration
+        elif use_gaps:
+            end_time = min(start_time + audio_duration, next_start)
+            subtitle_duration = end_time - start_time
+        elif subtitle_duration is None:
+            subtitle_duration = audio_duration
+            end_time = start_time + audio_duration
+
+        # Speed up if needed
+        speedup_threshold = next_start - start_time if use_gaps else subtitle_duration
+        if audio_duration > speedup_threshold and speedup_threshold > 0:
+            speed_factor = audio_duration / speedup_threshold
+            full_audio = speed_up_audio(
+                full_audio, speed_factor,
+                method=subtitle_speed_method,
+                backend=backend, text=processed_text,
+                voice=voice, base_speed=speed,
+                sample_rate=sample_rate,
+            )
+            audio_duration = len(full_audio) / sample_rate
+
+        # Adjust duration after speed change
+        if use_gaps:
+            end_time = min(start_time + audio_duration, next_start)
+            subtitle_duration = end_time - start_time
+        elif subtitle_duration is None:
+            subtitle_duration = audio_duration
+            end_time = start_time + audio_duration
+
+        # Pad or trim to subtitle duration
+        full_audio = fit_audio_to_duration(full_audio, subtitle_duration, sample_rate)
+
+        # Mix into buffer
+        start_sample = int(start_time * sample_rate)
+        audio_buffer = mix_audio(audio_buffer, full_audio, start_sample)
+
+        # Progress
+        if progress_callback:
+            percent = min(int(idx / total * 100), 99)
+            etr = calc_etr_str(time.time() - etr_start, idx, total)
+            progress_callback(percent, etr)
+
+    # Normalize if needed
+    if np.abs(audio_buffer).max() > 1.0:
+        logger.info("Normalizing audio (peak: %.2f)", np.abs(audio_buffer).max())
+        audio_buffer = normalize_audio(audio_buffer)
+
+    return audio_buffer

abogen/domain/text_chapters.py

@@ -0,0 +1,59 @@
+"""Chapter parsing from raw text.
+
+Provides a unified function for splitting text by chapter markers,
+used by both WebUI and PyQt conversion runners.
+"""
+
+from __future__ import annotations
+
+import re
+from typing import List, Tuple
+
+from abogen.subtitle_utils import clean_text
+
+
+_CHAPTER_MARKER_RE = re.compile(r"<<CHAPTER_MARKER:(.*?)>>", re.IGNORECASE)
+
+
+def parse_chapters_from_text(
+    text: str,
+    default_title: str = "text",
+    clean: bool = True,
+) -> List[Tuple[str, str]]:
+    """Split raw text into chapters using chapter marker patterns.
+
+    Preserves content before the first marker as "Introduction" if present.
+    Optionally applies clean_text() to each chapter segment.
+
+    Args:
+        text: Raw text possibly containing <<CHAPTER_MARKER:Title>> markers.
+        default_title: Fallback title when no markers are found.
+        clean: Whether to apply clean_text() to each segment.
+
+    Returns:
+        List of (title, text) tuples.
+    """
+    matches = list(_CHAPTER_MARKER_RE.finditer(text))
+    if not matches:
+        cleaned = clean_text(text) if clean else text
+        return [(default_title, cleaned)]
+
+    chapters: List[Tuple[str, str]] = []
+
+    # Preserve content before first marker as "Introduction"
+    first_start = matches[0].start()
+    if first_start > 0:
+        intro_text = text[:first_start].strip()
+        if intro_text:
+            chapters.append(("Introduction", clean_text(intro_text) if clean else intro_text))
+
+    for idx, match in enumerate(matches):
+        start = match.end()
+        end = matches[idx + 1].start() if idx + 1 < len(matches) else len(text)
+        chapter_name = match.group(1).strip() or default_title
+        chapter_text = text[start:end].strip()
+        if clean:
+            chapter_text = clean_text(chapter_text)
+        chapters.append((chapter_name, chapter_text))
+
+    return chapters

abogen/domain/text_utils.py

@@ -0,0 +1,22 @@
+"""Text utility functions for the domain layer."""
+
+from __future__ import annotations
+
+import re
+
+# Pre-compiled patterns for calculate_text_length
+_METADATA_TAG_PATTERN = re.compile(r"<<METADATA_[^:]+:[^>]*>>")
+_CHAPTER_MARKER_PATTERN = re.compile(r"<<CHAPTER_MARKER:[^>]*>>")
+_VOICE_MARKER_PATTERN = re.compile(r"<<VOICE:[^>]*>>")
+
+
+def calculate_text_length(text: str) -> int:
+    """Calculate character count, ignoring internal markers and newlines.
+
+    Strips chapter markers, voice markers, and metadata tags before counting.
+    """
+    text = _CHAPTER_MARKER_PATTERN.sub("", text)
+    text = _VOICE_MARKER_PATTERN.sub("", text)
+    text = _METADATA_TAG_PATTERN.sub("", text)
+    text = text.replace("\n", "").strip()
+    return len(text)

abogen/domain/title_builder.py

@@ -0,0 +1,97 @@
+from __future__ import annotations
+
+from pathlib import Path
+from typing import Any, List, Mapping, Optional
+
+from .metadata_helpers import (
+    ensure_sentence,
+    extract_series_metadata,
+    format_author_sentence,
+    format_series_sentence,
+    normalize_metadata_map,
+)
+
+
+def build_title_intro_text(
+    metadata: Optional[Mapping[str, Any]],
+    fallback_basename: str,
+) -> str:
+    """Build the title introduction text from metadata."""
+    normalized = normalize_metadata_map(metadata)
+    fallback_title = Path(fallback_basename).stem if fallback_basename else ""
+    title = (
+        normalized.get("title")
+        or normalized.get("book_title")
+        or normalized.get("album")
+        or fallback_title
+    )
+    if not title:
+        title = fallback_title
+    subtitle = normalized.get("subtitle") or normalized.get("sub_title")
+    if subtitle and title and subtitle.casefold() == title.casefold():
+        subtitle = ""
+
+    author_value = ""
+    for candidate in ("artist", "album_artist", "author", "authors", "writer", "composer"):
+        value = normalized.get(candidate)
+        if value:
+            author_value = value
+            break
+
+    series_name, series_number = extract_series_metadata(normalized)
+    series_sentence = format_series_sentence(series_name, series_number)
+
+    sentences: List[str] = []
+    if series_sentence:
+        sentences.append(ensure_sentence(series_sentence))
+    if title:
+        sentences.append(ensure_sentence(title))
+    if subtitle:
+        sentences.append(ensure_sentence(subtitle))
+    author_sentence = format_author_sentence(author_value)
+    if author_sentence:
+        sentences.append(ensure_sentence(author_sentence))
+    return " ".join(sentences).strip()
+
+
+def build_outro_text(
+    metadata: Optional[Mapping[str, Any]],
+    fallback_basename: str,
+) -> str:
+    """Build the outro/closing text from metadata."""
+    normalized = normalize_metadata_map(metadata)
+    fallback_title = Path(fallback_basename).stem if fallback_basename else ""
+    title = (
+        normalized.get("title")
+        or normalized.get("book_title")
+        or normalized.get("album")
+        or fallback_title
+    )
+    author_value = ""
+    for candidate in ("authors", "author", "album_artist", "artist", "writer", "composer"):
+        value = normalized.get(candidate)
+        if value:
+            author_value = value
+            break
+    author_sentence = format_author_sentence(author_value)
+    authors_fragment = (
+        author_sentence[3:].strip() if author_sentence.lower().startswith("by ") else author_sentence.strip()
+    )
+
+    if title and authors_fragment:
+        closing_line = f"The end of {title} from {authors_fragment}"
+    elif title:
+        closing_line = f"The end of {title}"
+    elif authors_fragment:
+        closing_line = f"The end from {authors_fragment}"
+    else:
+        closing_line = "The end"
+
+    series_name, series_number = extract_series_metadata(normalized)
+    series_sentence = format_series_sentence(series_name, series_number)
+
+    sentences: List[str] = [ensure_sentence(closing_line)]
+    if series_sentence:
+        sentences.append(ensure_sentence(series_sentence))
+
+    return " ".join(sentence for sentence in sentences if sentence).strip()

abogen/domain/tokens.py

@@ -0,0 +1,13 @@
+"""Shared token stubs for TTS processing."""
+
+from __future__ import annotations
+
+
+class FakeToken:
+    """Minimal token stub for languages without per-word token support."""
+
+    def __init__(self, text: str, start: float, end: float):
+        self.text = text
+        self.start_ts = start
+        self.end_ts = end
+        self.whitespace = ""

abogen/domain/voice_catalog.py

@@ -0,0 +1,112 @@
+"""Voice catalog — shared voice metadata for all UIs.
+
+Builds a unified catalog of available voices with metadata (language,
+gender, display name). Used by both WebUI and PyQt for voice selection UIs.
+"""
+
+from __future__ import annotations
+
+from typing import Any, Dict, Iterable, List, Mapping, Optional
+
+from abogen.constants import LANGUAGE_DESCRIPTIONS
+from abogen.tts_plugin.utils import get_voices
+
+
+def build_voice_catalog() -> List[Dict[str, str]]:
+    """Build voice catalog with metadata for all available voices.
+
+    Returns a list of dicts, each containing:
+        - id: voice ID (e.g. "af_heart")
+        - language: language code (e.g. "a", "e")
+        - language_label: human-readable language name
+        - gender: "Female", "Male", or "Unknown"
+        - gender_code: "f", "m", or ""
+        - display_name: human-readable voice name
+    """
+    from plugins.kokoro.engine import language_for_voice_id
+
+    catalog: List[Dict[str, str]] = []
+    gender_map = {"f": "Female", "m": "Male"}
+    for voice_id in get_voices("kokoro"):
+        prefix, _, rest = voice_id.partition("_")
+        gender_code = prefix[1] if len(prefix) > 1 else ""
+        lang = language_for_voice_id(voice_id)
+        catalog.append(
+            {
+                "id": voice_id,
+                "language": lang.value,
+                "language_label": LANGUAGE_DESCRIPTIONS.get(lang, lang.value.upper()),
+                "gender": gender_map.get(gender_code, "Unknown"),
+                "gender_code": gender_code,
+                "display_name": rest.replace("_", " ").title() if rest else voice_id,
+            }
+        )
+    return catalog
+
+
+def filter_voice_catalog(
+    catalog: Iterable[Mapping[str, Any]],
+    *,
+    gender: str,
+    allowed_languages: Optional[Iterable[str]] = None,
+) -> List[str]:
+    """Filter voice catalog by gender and language.
+
+    Returns voice IDs that match the criteria. Falls back to broader
+    matches if no exact matches are found.
+
+    Args:
+        catalog: Voice catalog entries (from build_voice_catalog).
+        gender: Gender filter ("male", "female", or "unknown").
+        allowed_languages: Optional list of allowed language codes.
+
+    Returns:
+        List of matching voice IDs.
+    """
+    allowed_set = {code.lower() for code in (allowed_languages or []) if isinstance(code, str) and code}
+    gender_normalized = (gender or "unknown").lower()
+    gender_code = ""
+    if gender_normalized == "male":
+        gender_code = "m"
+    elif gender_normalized == "female":
+        gender_code = "f"
+
+    matches: List[str] = []
+    seen: set[str] = set()
+
+    def _consider(entry: Mapping[str, Any]) -> None:
+        voice_id = entry.get("id")
+        if not isinstance(voice_id, str) or not voice_id:
+            return
+        if voice_id in seen:
+            return
+        seen.add(voice_id)
+        matches.append(voice_id)
+
+    primary: List[Mapping[str, Any]] = []
+    fallback: List[Mapping[str, Any]] = []
+    for entry in catalog:
+        if not isinstance(entry, Mapping):
+            continue
+        voice_lang = str(entry.get("language", "")).lower()
+        voice_gender_code = str(entry.get("gender_code", "")).lower()
+        if allowed_set and voice_lang not in allowed_set:
+            continue
+        if gender_code and voice_gender_code != gender_code:
+            fallback.append(entry)
+            continue
+        primary.append(entry)
+
+    for entry in primary:
+        _consider(entry)
+
+    if not matches:
+        for entry in fallback:
+            _consider(entry)
+
+    if not matches:
+        for entry in catalog:
+            if isinstance(entry, Mapping):
+                _consider(entry)
+
+    return matches

abogen/domain/voice_loader.py

@@ -0,0 +1,128 @@
+"""Voice loading and caching utilities.
+
+This module provides unified voice loading with caching support for both
+PyQt and WebUI interfaces.
+"""
+
+from __future__ import annotations
+
+from typing import Any, Dict, Optional
+
+from abogen.voice_formulas import get_new_voice
+
+
+class VoiceCache:
+    """Thread-safe voice cache for loaded voice tensors."""
+    
+    def __init__(self):
+        self._cache: Dict[str, Any] = {}
+    
+    def get(self, voice_spec: str) -> Optional[Any]:
+        """Get cached voice by spec."""
+        return self._cache.get(voice_spec)
+    
+    def set(self, voice_spec: str, voice: Any) -> None:
+        """Cache a loaded voice."""
+        self._cache[voice_spec] = voice
+    
+    def contains(self, voice_spec: str) -> bool:
+        """Check if voice is in cache."""
+        return voice_spec in self._cache
+    
+    def clear(self) -> None:
+        """Clear all cached voices."""
+        self._cache.clear()
+
+    def keys(self):
+        """Return cached voice specs."""
+        return self._cache.keys()
+
+    def __contains__(self, voice_spec: str) -> bool:
+        return self.contains(voice_spec)
+
+
+def resolve_voice(
+    voice_spec: str,
+    pipeline: Any,
+    use_gpu: bool,
+    cache: Optional[VoiceCache] = None,
+) -> Any:
+    """Resolve voice spec to actual voice tensor or name.
+    
+    If voice_spec contains '*' (formula), loads the voice using get_new_voice.
+    Otherwise, returns the voice_spec as-is (it's a voice name).
+    
+    Uses optional cache to avoid reloading same voice multiple times.
+    
+    Args:
+        voice_spec: Voice specification (name or formula string with '*').
+        pipeline: TTS pipeline instance for loading formula voices.
+        use_gpu: Whether to use GPU for voice loading.
+        cache: Optional VoiceCache instance for caching loaded voices.
+        
+    Returns:
+        Loaded voice tensor (for formulas) or voice name string.
+    """
+    # Check cache first
+    if cache and cache.contains(voice_spec):
+        return cache.get(voice_spec)
+
+    # Load voice
+    if "*" in voice_spec:
+        if pipeline is None or not hasattr(pipeline, "load_single_voice"):
+            return voice_spec
+        loaded_voice = get_new_voice(pipeline, voice_spec, use_gpu)
+    else:
+        loaded_voice = voice_spec
+    
+    # Cache it
+    if cache:
+        cache.set(voice_spec, loaded_voice)
+    
+    return loaded_voice
+
+
+def load_voice_cached(
+    voice_name: str,
+    pipeline: Any,
+    use_gpu: bool,
+    cache: Any = None,
+) -> Any:
+    """Load voice with caching (compatibility wrapper for PyQt).
+
+    This function maintains backward compatibility with the PyQt interface
+    while using the unified voice loading logic.
+
+    Args:
+        voice_name: Voice name or formula string.
+        pipeline: TTS pipeline instance.
+        use_gpu: Whether to use GPU.
+        cache: Optional VoiceCache or dict to use as cache.
+
+    Returns:
+        Loaded voice tensor or voice name string.
+    """
+    # Check cache (supports both VoiceCache and plain dict)
+    if cache is not None:
+        if isinstance(cache, VoiceCache):
+            if cache.contains(voice_name):
+                return cache.get(voice_name)
+        elif voice_name in cache:
+            return cache[voice_name]
+
+    # Load voice
+    if "*" in voice_name:
+        if pipeline is None or not hasattr(pipeline, "load_single_voice"):
+            return voice_name
+        loaded_voice = get_new_voice(pipeline, voice_name, use_gpu)
+    else:
+        loaded_voice = voice_name
+
+    # Cache it
+    if cache is not None:
+        if isinstance(cache, VoiceCache):
+            cache.set(voice_name, loaded_voice)
+        else:
+            cache[voice_name] = loaded_voice
+
+    return loaded_voice

abogen/domain/voice_markers.py

@@ -0,0 +1,117 @@
+"""Voice marker parsing and text splitting.
+
+Handles <<VOICE:name>> markers in text, splitting text into voice-specific
+segments. This is domain logic about text segmentation by voice, not subtitle
+processing.
+"""
+
+from __future__ import annotations
+
+import re
+from typing import List, Tuple
+
+_VOICE_MARKER_PATTERN = re.compile(r"<<VOICE:[^>]*>>")
+_VOICE_MARKER_SEARCH_PATTERN = re.compile(r"<<VOICE:(.*?)>>")
+
+
+def validate_voice_name(voice_name: str) -> Tuple[bool, str | None]:
+    """Validate voice name against available voices (case-insensitive).
+
+    Handles both single voices and formulas like 'af_heart*0.5 + am_echo*0.5'.
+
+    Returns:
+        Tuple of (is_valid, invalid_voice_name):
+            - is_valid: True if all voices in the name/formula are valid
+            - invalid_voice_name: The first invalid voice found, or None if all valid
+    """
+    from abogen.tts_plugin.utils import get_voices
+
+    voice_lookup_lower = {v.lower() for v in get_voices("kokoro")}
+    voice_name = voice_name.strip()
+
+    if "*" in voice_name:
+        voices = voice_name.split("+")
+        for term in voices:
+            if "*" in term:
+                base_voice = term.split("*")[0].strip()
+                if base_voice.lower() not in voice_lookup_lower:
+                    return False, base_voice
+        return True, None
+    else:
+        if voice_name.lower() not in voice_lookup_lower:
+            return False, voice_name
+        return True, None
+
+
+def split_text_by_voice_markers(
+    text: str, default_voice: str
+) -> Tuple[List[Tuple[str, str]], str, int, int]:
+    """Split text by voice markers, returning list of (voice, text) tuples.
+
+    Returns the last voice used so it can persist across chapters.
+    Voice names are normalized to lowercase to match canonical voice names.
+
+    Args:
+        text: Text potentially containing <<VOICE:name>> markers
+        default_voice: Voice to use if no markers found or before first marker
+
+    Returns:
+        Tuple of (segments_list, last_voice_used, valid_count, invalid_count):
+            - segments_list: List of (voice_name, segment_text) tuples
+            - last_voice_used: The voice that should continue into next chapter
+            - valid_count: Number of valid voice markers processed
+            - invalid_count: Number of invalid voice markers skipped
+    """
+    from abogen.tts_plugin.utils import get_voices
+
+    voice_splits = list(_VOICE_MARKER_SEARCH_PATTERN.finditer(text))
+
+    if not voice_splits:
+        return [(default_voice, text)], default_voice, 0, 0
+
+    segments: List[Tuple[str, str]] = []
+    current_voice = default_voice
+    valid_markers = 0
+    invalid_markers = 0
+
+    first_start = voice_splits[0].start()
+    if first_start > 0:
+        intro_text = text[:first_start].strip()
+        if intro_text:
+            segments.append((current_voice, intro_text))
+
+    for idx, match in enumerate(voice_splits):
+        voice_name = match.group(1).strip()
+        start = match.end()
+        end = voice_splits[idx + 1].start() if idx + 1 < len(voice_splits) else len(text)
+        segment_text = text[start:end].strip()
+
+        is_valid, invalid_voice = validate_voice_name(voice_name)
+        if is_valid:
+            if "*" in voice_name:
+                normalized_parts = []
+                for part in voice_name.split("+"):
+                    part = part.strip()
+                    if "*" in part:
+                        voice_part, weight = part.split("*", 1)
+                        voice_part_lower = voice_part.strip().lower()
+                        canonical_voice = next(
+                            (v for v in get_voices("kokoro") if v.lower() == voice_part_lower),
+                            voice_part.strip()
+                        )
+                        normalized_parts.append(f"{canonical_voice}*{weight.strip()}")
+                current_voice = " + ".join(normalized_parts)
+            else:
+                voice_name_lower = voice_name.lower()
+                current_voice = next(
+                    (v for v in get_voices("kokoro") if v.lower() == voice_name_lower),
+                    voice_name
+                )
+            valid_markers += 1
+        else:
+            invalid_markers += 1
+
+        if segment_text:
+            segments.append((current_voice, segment_text))
+
+    return segments, current_voice, valid_markers, invalid_markers

abogen/domain/voice_resolution.py

@@ -0,0 +1,355 @@
+"""Voice resolution helpers.
+
+Functions for resolving voice specifications, collecting required voice IDs,
+and determining the voice to use for chapters and chunks.
+
+All functions accept ConversionRequest (the app-layer contract) instead of
+UI-specific objects. This keeps the domain layer UI-agnostic.
+"""
+
+from __future__ import annotations
+
+from typing import Any, Dict, Mapping, Optional, Set, Tuple
+
+from abogen.tts_plugin.utils import get_voices, get_default_voice
+from abogen.voice_formulas import extract_voice_ids, pairs_to_formula
+from abogen.voice_cache import ensure_voice_assets
+
+
+def spec_to_voice_ids(spec: Any) -> Set[str]:
+    text = str(spec or "").strip()
+    if not text:
+        return set()
+    if text == "__custom_mix":
+        return set()
+    if "*" in text:
+        try:
+            return set(extract_voice_ids(text))
+        except ValueError:
+            return set()
+    if text in get_voices("kokoro"):
+        return {text}
+    return set()
+
+
+def _get_chapter_overrides(request: Any) -> list:
+    """Extract chapter overrides from ConversionRequest."""
+    cc = getattr(request, "chapter_chunk", None)
+    if cc is not None:
+        return getattr(cc, "chapter_overrides", []) or []
+    return []
+
+
+def _get_chunks(request: Any) -> list:
+    """Extract chunks from ConversionRequest."""
+    cc = getattr(request, "chapter_chunk", None)
+    if cc is not None:
+        return getattr(cc, "chunks", []) or []
+    return []
+
+
+def job_voice_fallback(request: Any) -> str:
+    base = str(getattr(request, "voice", "") or "").strip()
+    if base and base != "__custom_mix":
+        return base
+
+    speakers = getattr(request, "speakers", None)
+    if isinstance(speakers, dict):
+        narrator = speakers.get("narrator")
+        if isinstance(narrator, dict):
+            for key in ("resolved_voice", "voice_formula", "voice"):
+                value = narrator.get(key)
+                candidate = str(value or "").strip()
+                if candidate and candidate != "__custom_mix":
+                    return candidate
+        for payload in speakers.values() or []:
+            if not isinstance(payload, dict):
+                continue
+            for key in ("resolved_voice", "voice_formula", "voice"):
+                value = payload.get(key)
+                candidate = str(value or "").strip()
+                if candidate and candidate != "__custom_mix":
+                    return candidate
+
+    for chapter in _get_chapter_overrides(request):
+        if not isinstance(chapter, dict):
+            continue
+        for key in ("resolved_voice", "voice_formula", "voice"):
+            candidate = str(chapter.get(key) or "").strip()
+            if candidate and candidate != "__custom_mix":
+                return candidate
+
+    return ""
+
+
+def collect_required_voice_ids(request: Any) -> Set[str]:
+    voices: Set[str] = set()
+    voices.update(spec_to_voice_ids(request.voice))
+    voices.update(spec_to_voice_ids(job_voice_fallback(request)))
+
+    for chapter in _get_chapter_overrides(request):
+        if not isinstance(chapter, dict):
+            continue
+        for key in ("resolved_voice", "voice_formula", "voice"):
+            voices.update(spec_to_voice_ids(chapter.get(key)))
+
+    for chunk in _get_chunks(request):
+        if not isinstance(chunk, dict):
+            continue
+        for key in ("resolved_voice", "voice_formula", "voice"):
+            voices.update(spec_to_voice_ids(chunk.get(key)))
+
+    speakers = getattr(request, "speakers", {})
+    if isinstance(speakers, dict):
+        for payload in speakers.values() or []:
+            if not isinstance(payload, dict):
+                continue
+            for key in ("resolved_voice", "voice_formula", "voice"):
+                voices.update(spec_to_voice_ids(payload.get(key)))
+
+    voices.update(get_voices("kokoro"))
+    return voices
+
+
+def initialize_voice_cache(request: Any, events: Any = None) -> None:
+    """Initialize voice cache by downloading required voice assets.
+
+    Args:
+        request: ConversionRequest with voice/chapter/chunk/speaker info.
+        events: ConversionEvents for logging (optional, for backward compat).
+    """
+    log = (lambda msg, level="info": events.log(msg, level=level)) if events else (lambda msg, level="info": None)
+
+    try:
+        targets = collect_required_voice_ids(request)
+        downloaded, errors = ensure_voice_assets(
+            targets,
+            on_progress=lambda message: log(message, level="debug"),
+        )
+    except RuntimeError as exc:
+        log(f"Voice cache unavailable: {exc}", level="warning")
+        return
+
+    if downloaded:
+        log(
+            f"Cached {len(downloaded)} voice asset{'s' if len(downloaded) != 1 else ''} locally.",
+            level="info",
+        )
+
+    for voice_id, error in errors.items():
+        log(f"Failed to cache voice '{voice_id}': {error}", level="warning")
+
+
+def chapter_voice_spec(request: Any, override: Optional[Dict[str, Any]]) -> str:
+    if not override:
+        return job_voice_fallback(request)
+
+    resolved = str(override.get("resolved_voice", "")).strip()
+    if resolved:
+        return resolved
+
+    formula = str(override.get("voice_formula", "")).strip()
+    if formula:
+        return formula
+
+    voice = str(override.get("voice", "")).strip()
+    if voice:
+        return voice
+
+    return job_voice_fallback(request)
+
+
+def chunk_voice_spec(request: Any, chunk: Dict[str, Any], fallback: str) -> str:
+    for key in ("resolved_voice", "voice_formula", "voice"):
+        value = chunk.get(key)
+        if value:
+            return str(value)
+
+    speaker_id = chunk.get("speaker_id")
+    speakers = getattr(request, "speakers", None)
+    if isinstance(speakers, dict) and speaker_id in speakers:
+        speaker_entry = speakers.get(speaker_id) or {}
+        if isinstance(speaker_entry, dict):
+            for key in ("resolved_voice", "voice_formula", "voice"):
+                value = speaker_entry.get(key)
+                if value:
+                    return str(value)
+            profile_formula = speaker_entry.get("voice_formula")
+            if profile_formula:
+                return str(profile_formula)
+
+    profile_name = chunk.get("voice_profile")
+    if profile_name:
+        if isinstance(speakers, dict):
+            speaker_entry = speakers.get(profile_name)
+            if isinstance(speaker_entry, dict):
+                for key in ("resolved_voice", "voice_formula", "voice"):
+                    value = speaker_entry.get(key)
+                    if value:
+                        return str(value)
+
+    if fallback:
+        return fallback
+    return job_voice_fallback(request)
+
+
+def resolve_fallback_voice_spec(
+    base_spec: str,
+    job_voice: str,
+    voice_cache_keys: list[str],
+    provider: str = "kokoro",
+) -> str:
+    """Resolve the voice spec for intro/outro with a priority fallback chain.
+
+    Priority: base_spec → job_voice → first voice_cache key → default voice.
+    ``"__custom_mix"`` is treated as empty (it is not a usable voice spec).
+    """
+    spec = base_spec or job_voice
+    if spec == "__custom_mix":
+        spec = job_voice or ""
+    if not spec:
+        for key in voice_cache_keys:
+            if key and key != "__custom_mix":
+                spec = key.split(":", 1)[-1]
+                break
+    if not spec:
+        spec = get_default_voice(provider)
+    return spec
+
+
+# ---------------------------------------------------------------------------
+# Voice choice resolution (shared by all UIs)
+# ---------------------------------------------------------------------------
+
+
+def formula_from_profile(entry: Dict[str, Any]) -> Optional[str]:
+    """Convert a voice profile entry to a voice formula string.
+
+    Handles both Kokoro (voices list) and SuperTonic (single voice) profiles.
+    Returns None if the entry has no usable voice data.
+    """
+    if not isinstance(entry, dict):
+        return None
+    voices = entry.get("voices") or []
+    if not voices:
+        return None
+    return pairs_to_formula(voices)
+
+
+def resolve_profile_voice(
+    profile_name: Optional[str],
+    *,
+    profiles: Optional[Mapping[str, Any]] = None,
+) -> Tuple[str, Optional[str]]:
+    """Resolve a profile name to (formula, language).
+
+    Args:
+        profile_name: Name of the profile to resolve.
+        profiles: Pre-loaded profiles dict. If None, loads from disk.
+
+    Returns:
+        (formula_string, language_code) or ("", None) if not found.
+    """
+    if not profile_name:
+        return "", None
+    source = profiles if isinstance(profiles, Mapping) else None
+    if source is None:
+        from abogen.voice_profiles import load_profiles
+        source = load_profiles()
+    entry = source.get(profile_name) if isinstance(source, Mapping) else None
+    if not isinstance(entry, Mapping):
+        return "", None
+    formula = formula_from_profile(dict(entry)) or ""
+    language = entry.get("language") if isinstance(entry.get("language"), str) else None
+    if isinstance(language, str):
+        language = language.strip().lower() or None
+    return formula, language
+
+
+def resolve_voice_setting(
+    value: Any,
+    *,
+    profiles: Optional[Mapping[str, Any]] = None,
+) -> Tuple[str, Optional[str], Optional[str]]:
+    """Resolve a raw voice setting value into (spec, profile_name, language).
+
+    Parses 'profile:name' or 'speaker:name' prefixes and resolves
+    the profile to a formula string.
+
+    Args:
+        value: Raw voice value from user input (e.g. "af_heart", "profile:MyMix").
+        profiles: Pre-loaded profiles dict. If None, loads from disk.
+
+    Returns:
+        (resolved_spec, profile_name, language) — profile_name and language
+        are None when the input is a plain voice spec.
+    """
+    from abogen.domain.settings_core import split_profile_spec
+
+    base_spec, profile_name = split_profile_spec(value)
+    if profile_name:
+        formula, language = resolve_profile_voice(profile_name, profiles=profiles)
+        return formula or "", profile_name, language
+    return base_spec, None, None
+
+
+def resolve_voice_choice(
+    language: str,
+    base_voice: str,
+    profile_name: str,
+    custom_formula: str,
+    profiles: Dict[str, Any],
+) -> Tuple[str, str, Optional[str]]:
+    """Resolve a user's voice selection into (resolved_voice, resolved_language, selected_profile).
+
+    Handles three input modes:
+    1. Profile selection → resolves to formula (Kokoro) or speaker reference (SuperTonic)
+    2. Custom formula → used directly
+    3. Plain voice spec → passed through
+
+    Args:
+        language: Current language code (e.g. "a", "e").
+        base_voice: Base voice spec (voice ID or formula).
+        profile_name: Selected profile name (empty string if none).
+        custom_formula: Custom formula string (empty string if none).
+        profiles: Dict of all available profiles.
+
+    Returns:
+        (resolved_voice, resolved_language, selected_profile)
+    """
+    from abogen.voice_profiles import normalize_profile_entry
+
+    resolved_voice = base_voice
+    resolved_language = language
+    selected_profile = None
+
+    if profile_name:
+        entry_raw = profiles.get(profile_name)
+        entry = normalize_profile_entry(entry_raw)
+        provider = str((entry or {}).get("provider") or "").strip().lower()
+
+        # Provider-aware behavior:
+        # - Kokoro profiles typically represent mixes (formula strings).
+        # - SuperTonic profiles represent a discrete voice id + settings.
+        #   In that case, we return a speaker reference so downstream can
+        #   resolve provider per-speaker and allow mixed-provider casting.
+        if provider == "supertonic":
+            resolved_voice = f"speaker:{profile_name}"
+            selected_profile = profile_name
+            profile_language = (entry or {}).get("language")
+            if profile_language:
+                resolved_language = str(profile_language)
+        else:
+            formula = formula_from_profile(entry or {}) if entry else None
+            if formula:
+                resolved_voice = formula
+                selected_profile = profile_name
+                profile_language = (entry or {}).get("language")
+                if profile_language:
+                    resolved_language = profile_language
+
+    if custom_formula:
+        resolved_voice = custom_formula
+        selected_profile = None
+
+    return resolved_voice, resolved_language, selected_profile

abogen/domain/voice_utils.py

@@ -0,0 +1,129 @@
+from __future__ import annotations
+
+from typing import Any, Dict, Mapping, Optional, Tuple
+
+from abogen.tts_plugin.utils import get_voices
+
+
+def infer_provider_from_spec(value: Any, fallback: str = "kokoro") -> str:
+    """Infer TTS provider from voice specification."""
+    raw = str(value or "").strip()
+    if not raw:
+        return fallback
+    if raw.upper() == raw and raw.replace("_", "").isalnum():
+        return "supertonic"
+    if raw == "__custom_mix" or "*" in raw or "+" in raw:
+        return "kokoro"
+    if raw in get_voices("kokoro"):
+        return "kokoro"
+    return fallback
+
+
+def supertonic_voice_from_spec(spec: Any, fallback: str) -> str:
+    """Normalize a voice specification for Supertonic.
+
+    This function only performs Supertonic-specific normalization (uppercase conversion
+    and fallback handling). Backend resolution is handled by the registry.
+    """
+    raw = str(spec or "").strip()
+    fallback_raw = str(fallback or "").strip()
+
+    # Normalize to uppercase for Supertonic voice IDs
+    upper = raw.upper() if raw else ""
+
+    # If empty or contains formula characters, use fallback
+    if not upper or "*" in upper or "+" in upper:
+        upper = fallback_raw.upper() if fallback_raw else ""
+
+    # If still empty, use default Supertonic voice
+    if not upper or "*" in upper or "+" in upper:
+        upper = "M1"
+
+    return upper
+
+
+def split_speaker_reference(value: Any) -> Tuple[Optional[str], str]:
+    """Parse speaker/profile reference from string.
+
+    Expected format: "speaker:name" or "profile:name"
+    Returns (name, original) or (None, original) if not a valid reference.
+    """
+    raw = str(value or "").strip()
+    if not raw or ":" not in raw:
+        return None, raw
+    prefix, remainder = raw.split(":", 1)
+    prefix = prefix.strip().lower()
+    if prefix not in {"speaker", "profile"}:
+        return None, raw
+    name = remainder.strip()
+    return (name or None), raw
+
+
+def formula_from_kokoro_entry(entry: Mapping[str, Any]) -> str:
+    """Build voice formula string from kokoro entry."""
+    voices = entry.get("voices") or []
+    if not voices:
+        return ""
+    total = 0.0
+    parts: list[tuple[str, float]] = []
+    for item in voices:
+        if not isinstance(item, (list, tuple)) or len(item) < 2:
+            continue
+        name = str(item[0] or "").strip()
+        try:
+            weight = float(item[1])
+        except (TypeError, ValueError):
+            continue
+        if name and weight > 0:
+            parts.append((name, weight))
+            total += weight
+
+    if not parts:
+        return ""
+
+    normalized = [(name, weight / total) for name, weight in parts]
+    return " + ".join(f"{name}*{weight:.6f}" for name, weight in normalized)
+
+
+def coerce_truthy(value: Any, default: bool = True) -> bool:
+    """Coerce a value to boolean with default."""
+    if isinstance(value, bool):
+        return value
+    if isinstance(value, str):
+        return value.lower() not in {"false", "0", "no", "off", ""}
+    if value is None:
+        return default
+    return bool(value)
+
+
+def resolve_voice_target(
+    raw_spec: str,
+    normalized_profiles: Dict[str, Dict[str, Any]],
+    *,
+    job_voice: str = "M1",
+    job_tts_provider: str = "kokoro",
+    job_supertonic_total_steps: int = 5,
+    job_speed: float = 1.0,
+) -> Tuple[str, str, Optional[float], Optional[int]]:
+    """Resolve a raw voice spec into (provider, voice_spec, speed_override, steps_override).
+
+    Pure function — all dependencies are passed as parameters.
+    """
+    spec = str(raw_spec or "").strip()
+    speaker_name, _ = split_speaker_reference(spec)
+    if speaker_name and speaker_name in normalized_profiles:
+        entry = normalized_profiles[speaker_name]
+        provider = str(entry.get("provider") or "kokoro").strip().lower() or "kokoro"
+        if provider == "supertonic":
+            voice = str(entry.get("voice") or job_voice or "M1").strip() or "M1"
+            steps = int(entry.get("total_steps") or job_supertonic_total_steps or 5)
+            speed = float(entry.get("speed") or job_speed or 1.0)
+            return "supertonic", supertonic_voice_from_spec(voice, job_voice), speed, steps
+        formula = formula_from_kokoro_entry(entry)
+        return "kokoro", formula or spec, None, None
+
+    fallback_provider = str(job_tts_provider or "kokoro").strip().lower() or "kokoro"
+    inferred = infer_provider_from_spec(spec, fallback=fallback_provider)
+    if inferred == "supertonic":
+        return "supertonic", supertonic_voice_from_spec(spec, job_voice), None, None
+    return "kokoro", spec, None, None

abogen/epub3/exporter.py

@@ -12,6 +12,7 @@ from typing import Any, Dict, Iterable, List, Optional, Pattern, Sequence, Tuple
 import zipfile
 
 from abogen.text_extractor import ExtractedChapter, ExtractionResult
+from abogen.domain.metadata_helpers import normalize_metadata_map
 
 
 @dataclass(slots=True)
@@ -22,7 +23,7 @@ class ChunkOverlay:
     start: Optional[float]
     end: Optional[float]
     speaker_id: str
-    voice: Optional[str]
+    voice: Optional[Dict[str, str]]
     level: Optional[str] = None
     group_id: Optional[str] = None
 
@@ -59,7 +60,7 @@ class EPUB3PackageBuilder:
         self.output_path = output_path
         self.book_id = book_id or str(uuid.uuid4())
         self.extraction = extraction
-        self.metadata_tags = _normalize_metadata(metadata_tags)
+        self.metadata_tags = normalize_metadata_map(metadata_tags)
         self.chapter_markers = list(chapter_markers or [])
         self.chunk_markers = list(chunk_markers or [])
         self.chunks = list(chunks or [])
@@ -273,7 +274,7 @@ class EPUB3PackageBuilder:
                     start=_safe_float(marker.get("start")),
                     end=_safe_float(marker.get("end")),
                     speaker_id=speaker_id,
-                    voice=str(voice) if voice else None,
+                    voice=voice if isinstance(voice, dict) else None,
                     level=str(level) if level else None,
                     group_id=normalized_group_id,
                 )
@@ -516,9 +517,14 @@ def build_epub3_package(
     chunks: Iterable[Dict[str, Any]],
     audio_path: Path,
     speaker_mode: str = "single",
+    cover: "CoverConfig | None" = None,
     cover_image_path: Optional[Path] = None,
     cover_image_mime: Optional[str] = None,
 ) -> Path:
+    from abogen.domain.config_types import CoverConfig
+    if isinstance(cover, CoverConfig):
+        cover_image_path = cover.path
+        cover_image_mime = cover.mime
     builder = EPUB3PackageBuilder(
         output_path=output_path,
         book_id=book_id,
@@ -545,15 +551,6 @@ class ChunkLookup:
     by_chapter: Dict[int, List[Dict[str, Any]]]
 
 
-def _normalize_metadata(metadata: Optional[Dict[str, Any]]) -> Dict[str, str]:
-    normalized: Dict[str, str] = {}
-    for key, value in (metadata or {}).items():
-        if value is None:
-            continue
-        normalized[str(key).lower()] = str(value)
-    return normalized
-
-
 def _combine_metadata(*sources: Dict[str, Any]) -> Dict[str, str]:
     combined: Dict[str, str] = {}
     for source in sources:
@@ -696,7 +693,12 @@ def _group_chunks_for_render(chunks: Sequence[ChunkOverlay]) -> List[Tuple[Optio
 def _render_chunk_inline(chunk: ChunkOverlay) -> str:
     escaped_id = html.escape(chunk.id)
     speaker_attr = f" data-speaker=\"{html.escape(chunk.speaker_id)}\"" if chunk.speaker_id else ""
-    voice_attr = f" data-voice=\"{html.escape(chunk.voice)}\"" if chunk.voice else ""
+    voice_str = None
+    if chunk.voice and isinstance(chunk.voice, dict):
+        name = chunk.voice.get("voice", "")
+        provider = chunk.voice.get("provider", "")
+        voice_str = f"{name}@{provider}" if name and provider else name or None
+    voice_attr = f" data-voice=\"{html.escape(voice_str)}\"" if voice_str else ""
     level_attr = f" data-level=\"{html.escape(chunk.level)}\"" if chunk.level else ""
     raw_text = chunk.text or ""
     escaped_text = html.escape(raw_text)

abogen/hf_tracker.py

@@ -19,7 +19,7 @@ def tracked_hf_hub_download(*args, **kwargs):
     try:
         local_kwargs = dict(kwargs)
         local_kwargs["local_files_only"] = True
-        hf_hub_download(*args, **local_kwargs)
+        return hf_hub_download(*args, **local_kwargs)
     except Exception:
         repo_id = kwargs.get("repo_id", "<unknown repo>")
         filename = kwargs.get("filename", "<unknown file>")

abogen/infrastructure/exporters.py

@@ -0,0 +1,324 @@
+from __future__ import annotations
+
+import json
+import logging
+import tempfile
+from dataclasses import dataclass
+from pathlib import Path
+from typing import Any, Dict, List, Optional, Mapping, Sequence
+
+import static_ffmpeg
+
+from abogen.domain.metadata_helpers import (
+    split_people_field,
+    split_simple_list,
+    first_nonempty,
+    extract_year,
+    normalize_series_sequence,
+    _SERIES_SEQUENCE_TAG_KEYS,
+)
+from abogen.epub3.exporter import build_epub3_package
+from abogen.utils import create_process
+
+logger = logging.getLogger(__name__)
+
+
+@dataclass
+class ExportConfig:
+    """Configuration for export operations."""
+    ffmpeg_path: str = "ffmpeg"
+    verify_ssl: bool = True
+
+
+class ExportService:
+    """Unified service for audiobook exports (M4B, FFMETADATA, EPUB3, Audiobookshelf)."""
+    
+    def __init__(self, config: Optional[ExportConfig] = None):
+        self.config = config or ExportConfig()
+        static_ffmpeg.add_paths()
+    
+    # ----------------------------------------------------------------------
+    # FFMETADATA
+    # ----------------------------------------------------------------------
+    
+    def render_ffmetadata(
+        self,
+        metadata: Dict[str, Any],
+        chapters: List[Dict[str, Any]],
+    ) -> str:
+        """Render FFMETADATA content."""
+        lines = [";FFMETADATA1"]
+        
+        for key, value in (metadata or {}).items():
+            if value is None:
+                continue
+            key_str = str(key).strip()
+            if not key_str:
+                continue
+            lines.append(f"{key_str}={self._escape_ffmetadata_value(value)}")
+        
+        for chapter in chapters or []:
+            start = chapter.get("start")
+            end = chapter.get("end")
+            if start is None or end is None:
+                continue
+            try:
+                start_ms = max(0, int(round(float(start) * 1000)))
+                end_ms = int(round(float(end) * 1000))
+            except (TypeError, ValueError):
+                continue
+            if end_ms <= start_ms:
+                end_ms = start_ms + 1
+            lines.append("[CHAPTER]")
+            lines.append("TIMEBASE=1/1000")
+            lines.append(f"START={start_ms}")
+            lines.append(f"END={end_ms}")
+            title = chapter.get("title")
+            if title:
+                lines.append(f"title={self._escape_ffmetadata_value(title)}")
+            voices = chapter.get("voices")
+            if voices and isinstance(voices, list):
+                voice_str = ", ".join(
+                    f"{v.get('voice', '')}@{v.get('provider', '')}"
+                    for v in voices if v.get("voice")
+                )
+                if voice_str:
+                    lines.append(f"voice={self._escape_ffmetadata_value(voice_str)}")
+        
+        return "\n".join(lines) + "\n"
+    
+    @staticmethod
+    def _escape_ffmetadata_value(value: Any) -> str:
+        escaped = str(value).replace("\\", "\\\\").replace("\n", "\\n")
+        escaped = escaped.replace("=", "\\=").replace(";", "\\;").replace("#", "\\#")
+        return escaped
+    
+    def write_ffmetadata_file(
+        self,
+        audio_path: Path,
+        metadata: Dict[str, Any],
+        chapters: List[Dict[str, Any]],
+    ) -> Optional[Path]:
+        """Write FFMETADATA file to temp location."""
+        content = self.render_ffmetadata(metadata, chapters)
+        if content.strip() == ";FFMETADATA1":
+            return None
+        
+        directory = audio_path.parent if audio_path.parent.exists() else Path(tempfile.gettempdir())
+        with tempfile.NamedTemporaryFile(
+            mode="w",
+            encoding="utf-8",
+            suffix=".ffmeta",
+            delete=False,
+            dir=str(directory),
+        ) as handle:
+            handle.write(content)
+            return Path(handle.name)
+    
+    # ----------------------------------------------------------------------
+    # M4B Export
+    # ----------------------------------------------------------------------
+    
+    def embed_m4b_metadata(
+        self,
+        audio_path: Path,
+        metadata: Dict[str, Any],
+        chapters: List[Dict[str, Any]],
+        cover: "CoverConfig | None" = None,
+        cover_path: Optional[Path] = None,
+        cover_mime: Optional[str] = None,
+        log_callback: Optional[callable] = None,
+    ) -> None:
+        """Embed metadata and chapters into M4B file using FFmpeg + Mutagen."""
+        from abogen.domain.config_types import CoverConfig
+        if isinstance(cover, CoverConfig):
+            cover_path = cover.path
+            cover_mime = cover.mime
+        ffmetadata_path = self.write_ffmetadata_file(audio_path, metadata, chapters)
+        
+        metadata_args = self._metadata_to_ffmpeg_args(metadata)
+        
+        cmd = ["ffmpeg", "-y", "-i", str(audio_path)]
+        
+        if ffmetadata_path:
+            cmd.extend(["-f", "ffmetadata", "-i", str(ffmetadata_path)])
+        
+        if cover_path and cover_path.exists():
+            cmd.extend(["-i", str(cover_path)])
+            cmd.extend(["-map", "0:a"])
+            cmd.extend(["-map", "1:v:0", "-c:v:0", "mjpeg", "-disposition:v:0", "attached_pic"])
+            if cover_mime:
+                cmd.extend(["-metadata:s:v:0", f"mimetype={cover_mime}"])
+            cmd.extend(["-metadata:s:v:0", "title=Cover Art"])
+        else:
+            cmd.extend(["-map", "0:a"])
+        
+        cmd.extend(["-c:a", "copy"])
+        
+        if ffmetadata_path:
+            cmd.extend(["-map_metadata", "1", "-map_chapters", "1"])
+        else:
+            cmd.extend(["-map_metadata", "0"])
+        
+        if metadata_args:
+            cmd.extend(metadata_args)
+        
+        cmd.extend(["-movflags", "+faststart+use_metadata_tags"])
+        
+        temp_output = audio_path.with_suffix(audio_path.suffix + ".tmp")
+        if audio_path.suffix.lower() in {".m4b", ".mp4", ".m4a"}:
+            cmd.extend(["-f", "mp4"])
+        cmd.append(str(temp_output))
+        
+        if log_callback:
+            log_callback("Embedding metadata into M4B output")
+        
+        process = create_process(cmd, text=True)
+        return_code = process.wait()
+        
+        if ffmetadata_path and ffmetadata_path.exists():
+            try:
+                ffmetadata_path.unlink()
+            except OSError:
+                pass
+        
+        if return_code != 0:
+            if temp_output.exists():
+                temp_output.unlink(missing_ok=True)
+            raise RuntimeError(f"ffmpeg failed to embed metadata (exit code {return_code})")
+        
+        temp_output.replace(audio_path)
+        
+        if log_callback:
+            log_callback("Embedded metadata and chapters into M4B output", "info")
+        
+        # Apply chapters via Mutagen for better compatibility
+        self._apply_m4b_chapters_mutagen(audio_path, chapters, log_callback)
+    
+    @staticmethod
+    def _metadata_to_ffmpeg_args(metadata: Dict[str, Any]) -> List[str]:
+        args = []
+        for key, value in (metadata or {}).items():
+            if value in (None, ""):
+                continue
+            key_str = str(key).strip()
+            if not key_str:
+                continue
+            normalized_key = key_str.lower()
+            if normalized_key == "year":
+                ffmpeg_key = "date"
+            else:
+                ffmpeg_key = key_str
+            args.extend(["-metadata", f"{ffmpeg_key}={value}"])
+        return args
+    
+    def _apply_m4b_chapters_mutagen(
+        self,
+        audio_path: Path,
+        chapters: List[Dict[str, Any]],
+        log_callback: Optional[callable] = None,
+    ) -> bool:
+        """Apply chapter atoms using Mutagen."""
+        if not chapters:
+            return False
+        
+        try:
+            from fractions import Fraction
+            from mutagen.mp4 import MP4, MP4Chapter
+        except ImportError:
+            if log_callback:
+                log_callback("Unable to write MP4 chapter atoms because mutagen is not installed.", "warning")
+            return False
+        
+        try:
+            mp4 = MP4(str(audio_path))
+        except Exception as exc:
+            if log_callback:
+                log_callback(f"Failed to open m4b for chapter embedding: {exc}", "warning")
+            return False
+        
+        chapter_objects = []
+        for index, entry in enumerate(sorted(chapters, key=lambda item: float(item.get("start") or 0.0))):
+            start_raw = entry.get("start")
+            if start_raw is None:
+                continue
+            try:
+                start_seconds = max(0.0, float(start_raw))
+            except (TypeError, ValueError):
+                continue
+            
+            title_value = entry.get("title")
+            title_text = str(title_value) if title_value else f"Chapter {index + 1}"
+            
+            start_fraction = Fraction(int(round(start_seconds * 1000)), 1000)
+            chapter_atom = MP4Chapter(start_fraction, title_text)
+            
+            end_raw = entry.get("end")
+            if end_raw is not None:
+                try:
+                    end_seconds = float(end_raw)
+                except (TypeError, ValueError):
+                    end_seconds = None
+                if end_seconds is not None and end_seconds > start_seconds:
+                    chapter_atom.end = Fraction(int(round(end_seconds * 1000)), 1000)
+            
+            chapter_objects.append(chapter_atom)
+        
+        if not chapter_objects:
+            return False
+        
+        try:
+            mp4.chapters = chapter_objects
+            mp4.save()
+        except Exception as exc:
+            if log_callback:
+                log_callback(f"Failed to persist MP4 chapter atoms: {exc}", "warning")
+            return False
+        
+        if log_callback:
+            log_callback(f"Applied {len(chapter_objects)} chapter markers via mutagen", "info")
+        return True
+    
+    # ----------------------------------------------------------------------
+    # EPUB3 Export
+    # ----------------------------------------------------------------------
+    
+    def export_epub3(
+        self,
+        output_path: Path,
+        book_id: str,
+        extraction: Any,  # ExtractionResult
+        metadata_tags: Dict[str, Any],
+        chapter_markers: Sequence[Dict[str, Any]],
+        chunk_markers: Sequence[Dict[str, Any]],
+        chunks: Iterable[Dict[str, Any]],
+        audio_path: Path,
+        speaker_mode: str = "single",
+        cover_path: Optional[Path] = None,
+        cover_mime: Optional[str] = None,
+    ) -> Path:
+        """Export EPUB3 with media overlays."""
+        return build_epub3_package(
+            output_path=output_path,
+            book_id=book_id,
+            extraction=extraction,
+            metadata_tags=metadata_tags,
+            chapter_markers=chapter_markers,
+            chunk_markers=chunk_markers,
+            chunks=chunks,
+            audio_path=audio_path,
+            speaker_mode=speaker_mode,
+            cover_image_path=cover_path,
+            cover_image_mime=cover_mime,
+        )
+    
+
+        if value is None:
+            return default
+        return bool(value)
+
+
+__all__ = [
+    "ExportConfig",
+    "ExportService",
+]

abogen/infrastructure/subtitle_writer.py

@@ -0,0 +1,374 @@
+from __future__ import annotations
+
+from abc import ABC, abstractmethod
+from dataclasses import dataclass
+from enum import Enum
+from pathlib import Path
+from typing import List, Optional, TextIO
+
+from abogen.domain.enums import SubtitleFormat, SubtitleMode
+from abogen.subtitle_utils import clean_subtitle_text
+
+
+class SubtitleAlignment(Enum):
+    LEFT = "left"
+    CENTER = "center"
+    NARROW = "narrow"
+    CENTER_NARROW = "center_narrow"
+
+
+@dataclass
+class SubtitleConfig:
+    """Configuration for subtitle writer."""
+    format: SubtitleFormat
+    mode: SubtitleMode
+    alignment: SubtitleAlignment = SubtitleAlignment.LEFT
+    max_words: int = 50
+    highlight_color: str = "&H00FFFF00"  # ASS highlight color
+
+
+class SubtitleWriter(ABC):
+    """Abstract base class for subtitle writers."""
+    
+    def __init__(self, path: Path, config: SubtitleConfig):
+        self.path = path
+        self.config = config
+        self._file: Optional[TextIO] = None
+        self._index = 0
+        self._opened = False
+    
+    def open(self) -> None:
+        """Open the subtitle file and write header."""
+        if self._opened:
+            return
+        self._file = open(self.path, "w", encoding="utf-8", errors="replace")
+        self._write_header()
+        self._opened = True
+    
+    @abstractmethod
+    def _write_header(self) -> None:
+        pass
+    
+    def write_entry(
+        self,
+        start: float,
+        end: float,
+        text: str,
+        voice: Optional[str] = None,
+    ) -> None:
+        """Write a subtitle entry."""
+        if not self._opened:
+            self.open()
+        
+        text = clean_subtitle_text(text)
+        if not text:
+            return
+        
+        self._index += 1
+        self._write_entry(self._index, start, end, text, voice)
+    
+    @abstractmethod
+    def _write_entry(
+        self,
+        index: int,
+        start: float,
+        end: float,
+        text: str,
+        voice: Optional[str],
+    ) -> None:
+        pass
+    
+    def close(self) -> None:
+        """Close the subtitle file."""
+        if self._file:
+            self._file.close()
+            self._file = None
+            self._opened = False
+    
+    def __enter__(self) -> "SubtitleWriter":
+        self.open()
+        return self
+    
+    def __exit__(self, exc_type, exc_val, exc_tb) -> None:
+        self.close()
+
+
+class SrtWriter(SubtitleWriter):
+    """SRT subtitle writer."""
+    
+    def _write_header(self) -> None:
+        pass  # SRT has no header
+    
+    def _write_entry(
+        self,
+        index: int,
+        start: float,
+        end: float,
+        text: str,
+        voice: Optional[str],
+    ) -> None:
+        start_str = self._format_time(start)
+        end_str = self._format_time(end)
+        
+        if voice:
+            text = f"[{voice}] {text}"
+        
+        self._file.write(f"{index}\n")
+        self._file.write(f"{start_str} --> {end_str}\n")
+        self._file.write(f"{text}\n\n")
+    
+    @staticmethod
+    def _format_time(seconds: float) -> str:
+        hours = int(seconds // 3600)
+        minutes = int((seconds % 3600) // 60)
+        secs = int(seconds % 60)
+        millis = int((seconds - int(seconds)) * 1000)
+        return f"{hours:02d}:{minutes:02d}:{secs:02d},{millis:03d}"
+
+
+class VttWriter(SubtitleWriter):
+    """WebVTT subtitle writer."""
+    
+    def _write_header(self) -> None:
+        self._file.write("WEBVTT\n\n")
+    
+    def _write_entry(
+        self,
+        index: int,
+        start: float,
+        end: float,
+        text: str,
+        voice: Optional[str],
+    ) -> None:
+        start_str = self._format_time(start)
+        end_str = self._format_time(end)
+        
+        if voice:
+            text = f"[{voice}] {text}"
+        
+        self._file.write(f"{index}\n")
+        self._file.write(f"{start_str} --> {end_str}\n")
+        self._file.write(f"{text}\n\n")
+    
+    @staticmethod
+    def _format_time(seconds: float) -> str:
+        hours = int(seconds // 3600)
+        minutes = int((seconds % 3600) // 60)
+        secs = seconds % 60
+        return f"{hours:02d}:{minutes:02d}:{secs:06.3f}".replace(".", ".")
+
+
+class AssWriter(SubtitleWriter):
+    """ASS subtitle writer with karaoke highlighting support."""
+    
+    def __init__(self, path: Path, config: SubtitleConfig):
+        super().__init__(path, config)
+        self._is_centered = config.alignment in (SubtitleAlignment.CENTER, SubtitleAlignment.CENTER_NARROW)
+        self._is_narrow = config.alignment in (SubtitleAlignment.NARROW, SubtitleAlignment.CENTER_NARROW)
+    
+    def _write_header(self) -> None:
+        margin = "90" if self._is_narrow else "10"
+        alignment = "5" if self._is_centered else "2"
+        
+        self._file.write("[Script Info]\n")
+        self._file.write("Title: Generated by Abogen\n")
+        self._file.write("ScriptType: v4.00+\n\n")
+        
+        # Styles
+        self._file.write("[V4+ Styles]\n")
+        self._file.write(
+            "Format: Name, Fontname, Fontsize, PrimaryColour, SecondaryColour, "
+            "OutlineColour, BackColour, Bold, Italic, Underline, StrikeOut, "
+            "ScaleX, ScaleY, Spacing, Angle, BorderStyle, Outline, Shadow, "
+            "Alignment, MarginL, MarginR, MarginV, Encoding\n"
+        )
+        
+        if self.config.mode == SubtitleMode.SENTENCE_HIGHLIGHT:
+            # Karaoke style with highlighting
+            self._file.write(
+                f"Style: Default,Arial,24,&H00FFFFFF,&H00808080,&H00000000,&H00404040,"
+                f"0,0,0,0,100,100,0,0,3,2,0,{alignment},{margin},{margin},10,1\n"
+            )
+            self._file.write(
+                f"Style: Highlight,Arial,24,&H0000FFFF,&H00808080,&H00000000,&H00404040,"
+                f"0,0,0,0,100,100,0,0,3,2,0,{alignment},{margin},{margin},10,1\n\n"
+            )
+        else:
+            self._file.write(
+                f"Style: Default,Arial,24,&H00FFFFFF,&H00808080,&H00000000,&H00404040,"
+                f"0,0,0,0,100,100,0,0,3,2,0,{alignment},{margin},{margin},10,1\n\n"
+            )
+        
+        self._file.write("[Events]\n")
+        self._file.write(
+            "Format: Layer, Start, End, Style, Name, MarginL, MarginR, MarginV, Effect, Text\n"
+        )
+    
+    def _write_entry(
+        self,
+        index: int,
+        start: float,
+        end: float,
+        text: str,
+        voice: Optional[str],
+    ) -> None:
+        start_str = self._format_time(start)
+        end_str = self._format_time(end)
+        
+        if voice:
+            text = f"[{voice}] {text}"
+        
+        style = "Default"
+        if self.config.mode == SubtitleMode.SENTENCE_HIGHLIGHT:
+            # Add karaoke tags for highlighting
+            text = self._add_karaoke_tags(text)
+            style = "Highlight"
+        
+        alignment_tag = r"{\an5}" if self._is_centered else ""
+        self._file.write(
+            f"Dialogue: 0,{start_str},{end_str},{style},,0,0,0,,{alignment_tag}{text}\n"
+        )
+    
+    def _add_karaoke_tags(self, text: str) -> str:
+        """Add karaoke highlighting tags to text."""
+        # Simple word-level karaoke timing
+        words = text.split()
+        if not words:
+            return text
+        
+        # This is a simplified version - real karaoke needs per-word timing
+        # For now, just return the text with the highlight color
+        return r"{\k100}" + r"{\k100}".join(words) + r"{\k0}"
+    
+    @staticmethod
+    def _format_time(seconds: float) -> str:
+        hours = int(seconds // 3600)
+        minutes = int((seconds % 3600) // 60)
+        secs = seconds % 60
+        return f"{hours}:{minutes:02d}:{secs:05.2f}"
+
+
+def create_subtitle_writer(
+    path: Path,
+    format: str,
+    mode: str,
+    alignment: str = "left",
+    max_words: int = 50,
+) -> SubtitleWriter:
+    """Factory function to create subtitle writer."""
+    fmt = SubtitleFormat(format.lower())
+    mode = SubtitleMode(mode)
+    align = SubtitleAlignment(alignment.lower())
+
+    config = SubtitleConfig(
+        format=fmt,
+        mode=mode,
+        alignment=align,
+        max_words=max_words,
+    )
+
+    if fmt == SubtitleFormat.SRT:
+        return SrtWriter(path, config)
+    elif fmt == SubtitleFormat.VTT:
+        return VttWriter(path, config)
+    elif fmt == SubtitleFormat.ASS:
+        return AssWriter(path, config)
+    else:
+        raise ValueError(f"Unsupported subtitle format: {format}")
+
+
+def resolve_subtitle_format(
+    subtitle: "SubtitleConfig | str | None",
+    subtitle_mode: str | None = None,
+) -> tuple[str, str]:
+    """Resolve a subtitle config to (file_extension, alignment).
+
+    Accepts a SubtitleConfig object or individual format/mode strings
+    for backward compatibility.
+
+    Returns:
+        Tuple of (file_extension, alignment) suitable for
+        :func:`create_subtitle_writer`.
+    """
+    from abogen.domain.config_types import SubtitleConfig
+
+    if isinstance(subtitle, SubtitleConfig):
+        fmt = subtitle.format.value.lower()
+        mode_str = subtitle.mode.value
+    else:
+        fmt = (subtitle or "srt").lower()
+        mode_str = subtitle_mode or "Disabled"
+
+    if mode_str == "Sentence + Highlighting" and fmt == "srt":
+        fmt = "ass"
+
+    if "ass" in fmt:
+        extension = "ass"
+        if "centered_narrow" in fmt:
+            alignment = "center_narrow"
+        elif "centered" in fmt:
+            alignment = "center"
+        elif "narrow" in fmt:
+            alignment = "narrow"
+        else:
+            alignment = "left"
+    else:
+        extension = fmt if fmt in ("srt", "vtt") else "srt"
+        alignment = "left"
+
+    return extension, alignment
+
+
+def make_subtitle_writer(
+    audio_path: Path,
+    subtitle: "SubtitleConfig | str | None",
+    subtitle_mode: str | None = None,
+    max_words: int | None = None,
+) -> SubtitleWriter | None:
+    """Convenience: resolve format and create a writer, or return None if disabled.
+
+    Accepts a SubtitleConfig object or individual format/mode strings
+    for backward compatibility.
+
+    Returns ``None`` when subtitle mode is ``"Disabled"`` or the
+    format is unsupported.
+    """
+    from abogen.domain.config_types import SubtitleConfig
+
+    if isinstance(subtitle, SubtitleConfig):
+        mode_str = subtitle.mode.value
+        if mode_str == "Disabled":
+            return None
+        words = subtitle.max_words
+    else:
+        mode_str = subtitle_mode or subtitle or "Disabled"
+        if mode_str == "Disabled":
+            return None
+        words = max_words or 50
+
+    extension, alignment = resolve_subtitle_format(subtitle, subtitle_mode)
+    try:
+        return create_subtitle_writer(
+            audio_path.with_suffix(f".{extension}"),
+            extension,
+            mode_str,
+            alignment=alignment,
+            max_words=words,
+        )
+    except (ValueError, KeyError):
+        return None
+
+
+__all__ = [
+    "SubtitleFormat",
+    "SubtitleMode",
+    "SubtitleAlignment",
+    "SubtitleConfig",
+    "SubtitleWriter",
+    "SrtWriter",
+    "VttWriter",
+    "AssWriter",
+    "create_subtitle_writer",
+    "resolve_subtitle_format",
+    "make_subtitle_writer",
+]

abogen/integrations/audiobookshelf.py

@@ -2,9 +2,7 @@ from __future__ import annotations
 
 import json
 import logging
-import math
 import mimetypes
-import re
 from contextlib import ExitStack
 from dataclasses import dataclass
 from pathlib import Path
@@ -12,6 +10,8 @@ from typing import Any, Dict, Iterable, List, Mapping, Optional, Sequence, Tuple
 
 import httpx
 
+from abogen.domain.metadata_helpers import normalize_series_sequence
+
 logger = logging.getLogger(__name__)
 
 
@@ -641,40 +641,7 @@ class AudiobookshelfClient:
         for key in preferred_keys:
             if key not in metadata:
                 continue
-            normalized = AudiobookshelfClient._normalize_series_sequence(metadata.get(key))
+            normalized = normalize_series_sequence(metadata.get(key))
             if normalized:
                 return normalized
         return ""
-
-    @staticmethod
-    def _normalize_series_sequence(raw: Any) -> str:
-        if raw is None:
-            return ""
-
-        if isinstance(raw, (int, float)):
-            if isinstance(raw, float) and (math.isnan(raw) or math.isinf(raw)):
-                return ""
-            text = str(raw)
-        else:
-            text = str(raw).strip()
-
-        if not text:
-            return ""
-
-        candidate = text.replace(",", ".")
-        match = re.search(r"\d+(?:\.\d+)?", candidate)
-        if not match:
-            return ""
-
-        normalized = match.group(0)
-        if "." in normalized:
-            normalized = normalized.rstrip("0").rstrip(".")
-            if not normalized:
-                normalized = "0"
-            return normalized
-
-        try:
-            return str(int(normalized))
-        except ValueError:
-            cleaned = normalized.lstrip("0")
-            return cleaned or "0"

abogen/main.py

@@ -2,13 +2,14 @@
 
 from __future__ import annotations
 
-import atexit
 import os
 import platform
-import signal
-import sys
 
-from abogen.utils import load_config, prevent_sleep_end
+# Initialise global shutdown handling (atexit, signals, Qt) as early as possible.
+from abogen import shutdown  # noqa: F401
+shutdown.register_shutdown()
+
+from abogen.utils import load_config
 from abogen.webui.app import main as _run_web_ui
 
 # Configure Hugging Face Hub behaviour (mirrors legacy GUI defaults).
@@ -27,17 +28,6 @@ os.environ.setdefault("MIOPEN_CONV_PRECISE_ROCM_TUNING", "0")
 if platform.system() == "Darwin" and platform.processor() == "arm":
     os.environ.setdefault("PYTORCH_ENABLE_MPS_FALLBACK", "1")
 
-atexit.register(prevent_sleep_end)
-
-
-def _cleanup_sleep(signum, _frame):
-    prevent_sleep_end()
-    sys.exit(0)
-
-
-signal.signal(signal.SIGINT, _cleanup_sleep)
-signal.signal(signal.SIGTERM, _cleanup_sleep)
-
 
 def main() -> None:
     """Launch the Flask-based web UI."""

abogen/predownload_gui.py

@@ -21,7 +21,8 @@ from PyQt6.QtWidgets import (
 )
 from PyQt6.QtCore import QThread, pyqtSignal
 
-from abogen.constants import COLORS, VOICES_INTERNAL
+from abogen.constants import COLORS
+from abogen.tts_plugin.utils import get_voices
 from abogen.spacy_utils import SPACY_MODELS
 import abogen.hf_tracker
 
@@ -114,7 +115,7 @@ class PreDownloadWorker(QThread):
             self._voices_success = False
             return
 
-        voice_list = VOICES_INTERNAL
+        voice_list = get_voices("kokoro")
         for idx, voice in enumerate(voice_list, start=1):
             if self._cancelled:
                 self._voices_success = False
@@ -462,14 +463,14 @@ class PreDownloadDialog(QDialog):
         try:
             from huggingface_hub import try_to_load_from_cache
 
-            for voice in VOICES_INTERNAL:
+            for voice in get_voices("kokoro"):
                 if not try_to_load_from_cache(
                     repo_id="hexgrad/Kokoro-82M", filename=f"voices/{voice}.pt"
                 ):
                     missing.append(voice)
         except Exception:
             # If HF missing, report all as missing
-            return False, list(VOICES_INTERNAL)
+            return False, list(get_voices("kokoro"))
         return (len(missing) == 0), missing
 
     def _check_kokoro_model(self) -> bool:

abogen/pyqt/book_handler.py

@@ -29,12 +29,16 @@ from abogen.utils import (
     get_resource_path,
 )
 from abogen.book_parser import get_book_parser
-
-from abogen.subtitle_utils import (
-    clean_text,
-    calculate_text_length,
+from abogen.domain.metadata_extraction import (
+    extract_book_metadata_epub,
+    extract_book_metadata_pdf,
+    extract_book_metadata_markdown,
+    format_metadata_tags,
 )
 
+from abogen.subtitle_utils import clean_text
+from abogen.domain.text_utils import calculate_text_length
+
 import os
 import logging
 import urllib.parse
@@ -948,169 +952,14 @@ class HandlerDialog(QDialog):
         self.previewEdit.setHtml(html_content)
 
     def _extract_book_metadata(self):
-        metadata = {
-            "title": None,
-            "authors": [],
-            "description": None,
-            "cover_image": None,
-            "publisher": None,
-            "publication_year": None,
-        }
-
         if self.parser.file_type == "epub":
-            try:
-                title_items = self.book.get_metadata("DC", "title")
-                if title_items and len(title_items) > 0:
-                    metadata["title"] = title_items[0][0]
-            except Exception as e:
-                logging.warning(f"Error extracting title metadata: {e}")
-
-            try:
-                author_items = self.book.get_metadata("DC", "creator")
-                if author_items:
-                    metadata["authors"] = [
-                        author[0] for author in author_items if len(author) > 0
-                    ]
-            except Exception as e:
-                logging.warning(f"Error extracting author metadata: {e}")
-
-            try:
-                desc_items = self.book.get_metadata("DC", "description")
-                if desc_items and len(desc_items) > 0:
-                    metadata["description"] = desc_items[0][0]
-            except Exception as e:
-                logging.warning(f"Error extracting description metadata: {e}")
-
-            try:
-                publisher_items = self.book.get_metadata("DC", "publisher")
-                if publisher_items and len(publisher_items) > 0:
-                    metadata["publisher"] = publisher_items[0][0]
-            except Exception as e:
-                logging.warning(f"Error extracting publisher metadata: {e}")
-
-            # Try to extract publication year
-            try:
-                date_items = self.book.get_metadata("DC", "date")
-                if date_items and len(date_items) > 0:
-                    date_str = date_items[0][0]
-                    # Try to extract just the year from the date string
-                    year_match = re.search(r"\b(19|20)\d{2}\b", date_str)
-                    if year_match:
-                        metadata["publication_year"] = year_match.group(0)
-                    else:
-                        metadata["publication_year"] = date_str
-            except Exception as e:
-                logging.warning(f"Error extracting publication date metadata: {e}")
-
-            for item in self.book.get_items_of_type(ebooklib.ITEM_COVER):
-                metadata["cover_image"] = item.get_content()
-                break
-
-            if not metadata["cover_image"]:
-                for item in self.book.get_items_of_type(ebooklib.ITEM_IMAGE):
-                    if "cover" in item.get_name().lower():
-                        metadata["cover_image"] = item.get_content()
-                        break
+            return extract_book_metadata_epub(self.book)
         elif self.parser.file_type == "markdown":
-            # Extract metadata from markdown frontmatter or first heading
-            if self.markdown_text:
-                # Try to extract YAML frontmatter
-                frontmatter_match = re.match(
-                    r"^---\s*\n(.*?)\n---\s*\n", self.markdown_text, re.DOTALL
+            return extract_book_metadata_markdown(
+                self.markdown_text, self.markdown_toc
             )
-                if frontmatter_match:
-                    try:
-                        frontmatter = frontmatter_match.group(1)
-                        # Simple YAML-like parsing for common fields
-                        title_match = re.search(
-                            r"^title:\s*(.+)$",
-                            frontmatter,
-                            re.MULTILINE | re.IGNORECASE,
-                        )
-                        if title_match:
-                            metadata["title"] = (
-                                title_match.group(1).strip().strip("\"'")
-                            )
-
-                        author_match = re.search(
-                            r"^author:\s*(.+)$",
-                            frontmatter,
-                            re.MULTILINE | re.IGNORECASE,
-                        )
-                        if author_match:
-                            metadata["authors"] = [
-                                author_match.group(1).strip().strip("\"'")
-                            ]
-
-                        desc_match = re.search(
-                            r"^description:\s*(.+)$",
-                            frontmatter,
-                            re.MULTILINE | re.IGNORECASE,
-                        )
-                        if desc_match:
-                            metadata["description"] = (
-                                desc_match.group(1).strip().strip("\"'")
-                            )
-
-                        date_match = re.search(
-                            r"^date:\s*(.+)$", frontmatter, re.MULTILINE | re.IGNORECASE
-                        )
-                        if date_match:
-                            date_str = date_match.group(1).strip().strip("\"'")
-                            year_match = re.search(r"\b(19|20)\d{2}\b", date_str)
-                            if year_match:
-                                metadata["publication_year"] = year_match.group(0)
-                    except Exception as e:
-                        logging.warning(f"Error parsing markdown frontmatter: {e}")
-
-                # Fallback: use first H1 header as title if no frontmatter title
-                if not metadata["title"] and self.markdown_toc:
-                    # Find the first level 1 header
-                    first_h1 = next(
-                        (h for h in self.markdown_toc if h["level"] == 1), None
-                    )
-                    if first_h1:
-                        metadata["title"] = first_h1["name"]
         else:
-            pdf_info = self.pdf_doc.metadata
-            if pdf_info:
-                metadata["title"] = pdf_info.get("title", None)
-
-                author = pdf_info.get("author", None)
-                if author:
-                    metadata["authors"] = [author]
-
-                metadata["description"] = pdf_info.get("subject", None)
-
-                keywords = pdf_info.get("keywords", None)
-                if keywords:
-                    if metadata["description"]:
-                        metadata["description"] += f"\n\nKeywords: {keywords}"
-                    else:
-                        metadata["description"] = f"Keywords: {keywords}"
-
-                metadata["publisher"] = pdf_info.get("creator", None)
-
-                # Try to extract publication date from PDF metadata
-                if "creationDate" in pdf_info:
-                    date_str = pdf_info["creationDate"]
-                    year_match = re.search(r"D:(\d{4})", date_str)
-                    if year_match:
-                        metadata["publication_year"] = year_match.group(1)
-                elif "modDate" in pdf_info:
-                    date_str = pdf_info["modDate"]
-                    year_match = re.search(r"D:(\d{4})", date_str)
-                    if year_match:
-                        metadata["publication_year"] = year_match.group(1)
-
-            if len(self.pdf_doc) > 0:
-                try:
-                    pix = self.pdf_doc[0].get_pixmap(matrix=fitz.Matrix(2, 2))
-                    metadata["cover_image"] = pix.tobytes("png")
-                except Exception:
-                    pass
-
-        return metadata
+            return extract_book_metadata_pdf(self.pdf_doc)
 
     def get_selected_text(self):
         # If a background loader thread is running, wait for it to finish to
@@ -1136,58 +985,20 @@ class HandlerDialog(QDialog):
 
     def _format_metadata_tags(self):
         """Format metadata tags for insertion at the beginning of the text"""
-        import datetime
         from abogen.utils import get_user_cache_path
 
-        metadata = self.book_metadata
         filename = os.path.splitext(os.path.basename(self.book_path))[0]
-        current_year = str(datetime.datetime.now().year)
-
-        # Get values with fallbacks
-        title = metadata.get("title") or filename
-        authors = metadata.get("authors") or ["Unknown"]
-        authors_text = ", ".join(authors)
-        album_artist = authors_text or "Unknown"
-        year = (
-            metadata.get("publication_year") or current_year
-        )  # Use publication year if available
-
-        # Count chapters/pages
-        total_chapters = len(self.checked_chapters)
-        chapter_text = (
-            f"{total_chapters} {'Chapters' if self.parser.file_type == 'epub' else 'Pages'}"
-        )
-
-        # Handle cover image
-        cover_tag = ""
-        if metadata.get("cover_image"):
-            try:
-                import uuid
-
+        chapter_count = len(self.checked_chapters)
         cache_dir = get_user_cache_path()
-                cover_path = os.path.join(cache_dir, f"cover_{uuid.uuid4()}.jpg")
-                cover_path = os.path.normpath(cover_path)
-                with open(cover_path, "wb") as f:
-                    f.write(metadata["cover_image"])
-                cover_tag = f"<<METADATA_COVER_PATH:{cover_path}>>"
-            except Exception as e:
-                logging.warning(f"Failed to save cover image: {e}")
 
-        # Format metadata tags
-        metadata_tags = [
-            f"<<METADATA_TITLE:{title}>>",
-            f"<<METADATA_ARTIST:{authors_text}>>",
-            f"<<METADATA_ALBUM:{title} ({chapter_text})>>",
-            f"<<METADATA_YEAR:{year}>>",
-            f"<<METADATA_ALBUM_ARTIST:{album_artist}>>",
-            f"<<METADATA_COMPOSER:Narrator>>",
-            f"<<METADATA_GENRE:Audiobook>>",
-        ]
-
-        if cover_tag:
-            metadata_tags.append(cover_tag)
-
-        return "\n".join(metadata_tags)
+        return format_metadata_tags(
+            self.book_metadata,
+            filename,
+            chapter_count,
+            self.parser.file_type,
+            cover_bytes=self.book_metadata.get("cover_image"),
+            cache_dir=cache_dir,
+        )
 
     def _get_markdown_selected_text(self):
         """Get selected text from markdown chapters"""

abogen/pyqt/conversion_adapter.py

@@ -0,0 +1,209 @@
+"""PyQt adapter: ConversionThread -> ConversionRequest.
+
+Converts a PyQt ConversionThread into a ConversionRequest that the application layer can process.
+This adapter is the bridge between the PyQt layer and the application/domain layer.
+
+The adapter is responsible for:
+- Mapping ConversionThread fields to ConversionRequest fields
+- Handling UI-specific state (signals, dialogs, cancellation)
+- Providing PipelineProvider and VoiceResolver implementations
+
+Subtitle file/timestamp special paths remain in ConversionThread.run() early return.
+"""
+
+from __future__ import annotations
+
+import os
+from pathlib import Path
+from typing import Any, Callable, Dict, List, Optional
+
+from abogen.application.conversion_config import (
+    ChapterChunkConfig,
+    Epub3ExportConfig,
+    PronunciationConfig,
+    WordSubstitutionConfig,
+)
+from abogen.application.conversion_request import ConversionRequest
+from abogen.application.conversion_ports import ConversionCancelled, ResolvedVoice
+
+
+def build_conversion_request_from_thread(thread: Any) -> ConversionRequest:
+    """Convert a PyQt ConversionThread into a ConversionRequest.
+
+    This is the primary function that maps thread fields to ConversionRequest.
+    All fields are copied — the request is independent of the thread.
+
+    Args:
+        thread: PyQt ConversionThread instance
+
+    Returns:
+        ConversionRequest with all thread data mapped
+    """
+    # Determine source path
+    source_path = None
+    is_direct_text = getattr(thread, "is_direct_text", False)
+    if not is_direct_text and thread.file_name:
+        source_path = Path(thread.file_name)
+
+    # Determine original filename
+    original_filename = ""
+    if getattr(thread, "from_queue", False):
+        base_path = getattr(thread, "save_base_path", None) or thread.file_name
+    else:
+        base_path = getattr(thread, "display_path", None) or thread.file_name
+
+    if base_path:
+        original_filename = os.path.basename(base_path)
+
+    # Determine output folder
+    output_folder = None
+    if thread.output_folder:
+        output_folder = Path(thread.output_folder)
+
+    # Build pronunciation config
+    pronunciation = None
+    pron_overrides = getattr(thread, "pronunciation_overrides", []) or []
+    manual_overrides = getattr(thread, "manual_overrides", []) or []
+    heteronym_overrides = getattr(thread, "heteronym_overrides", []) or []
+    norm_overrides = getattr(thread, "normalization_overrides", None)
+    if pron_overrides or manual_overrides or heteronym_overrides or norm_overrides:
+        pronunciation = PronunciationConfig(
+            pronunciation_overrides=pron_overrides,
+            manual_overrides=manual_overrides,
+            heteronym_overrides=heteronym_overrides,
+            normalization_overrides=norm_overrides,
+        )
+
+    # Build epub3 config
+    epub3_export = None
+    if getattr(thread, "generate_epub3", False):
+        epub3_export = Epub3ExportConfig()
+
+    return ConversionRequest(
+        # Source
+        source_path=source_path,
+        direct_text=thread.file_name if is_direct_text else None,
+        original_filename=original_filename,
+        # TTS Settings
+        language=thread.lang_code,
+        tts_provider="kokoro",  # PyQt uses Kokoro by default
+        voice=thread.voice,
+        voice_profile=getattr(thread, "voice_profile", None),
+        speed=thread.speed,
+        use_gpu=thread.use_gpu,
+        supertonic_total_steps=getattr(thread, "supertonic_total_steps", 5),
+        # Output Format
+        output_format=thread.output_format,
+        subtitle_mode=thread.subtitle_mode,
+        subtitle_format=getattr(thread, "subtitle_format", "srt"),
+        max_subtitle_words=getattr(thread, "max_subtitle_words", 50),
+        # Save Options
+        save_mode=thread.save_option,
+        output_folder=output_folder,
+        save_chapters_separately=getattr(thread, "save_chapters_separately", False),
+        merge_chapters_at_end=getattr(thread, "merge_chapters_at_end", True),
+        separate_chapters_format=getattr(thread, "separate_chapters_format", "wav"),
+        save_as_project=getattr(thread, "save_as_project", False),
+        # Timing
+        silence_between_chapters=getattr(thread, "silence_duration", 2.0),
+        chapter_intro_delay=getattr(thread, "chapter_intro_delay", 0.0),
+        # Content Processing
+        replace_single_newlines=getattr(thread, "replace_single_newlines", False),
+        read_title_intro=getattr(thread, "read_title_intro", False),
+        read_closing_outro=getattr(thread, "read_closing_outro", True),
+        auto_prefix_chapter_titles=getattr(thread, "auto_prefix_chapter_titles", True),
+        normalize_chapter_opening_caps=thread.normalize_chapter_opening_caps,
+        # Metadata
+        metadata_tags=getattr(thread, "metadata_tags", {}) or {},
+        # Artifacts
+        cover_image_path=getattr(thread, "cover_image_path", None),
+        cover_image_mime=getattr(thread, "cover_image_mime", None),
+        # Feature configs
+        pronunciation=pronunciation,
+        epub3_export=epub3_export,
+        chapter_chunk=ChapterChunkConfig(),  # PyQt doesn't use chapter overrides from GUI
+    )
+
+
+class PyQtEvents:
+    """PyQt implementation of ConversionEvents protocol.
+
+    Wraps a ConversionThread to provide logging, progress, and cancellation.
+    """
+
+    def __init__(self, thread: Any):
+        self._thread = thread
+
+    def log(self, message: str, level: str = "info") -> None:
+        """Log a message via signal."""
+        self._thread.log_updated.emit((message, _level_to_color(level)))
+
+    def progress(self, pct: int, etr: str) -> None:
+        """Update progress via signal."""
+        self._thread.progress_updated.emit(pct, etr)
+
+    def check_cancelled(self) -> None:
+        """Check if conversion was cancelled.
+
+        Raises:
+            ConversionCancelled: If cancellation was requested
+        """
+        if self._thread.cancel_requested:
+            raise ConversionCancelled("Conversion cancelled by user")
+
+
+class PyQtPipelineProvider:
+    """PyQt implementation of PipelineProvider protocol.
+
+    Wraps the existing backend from ConversionThread.
+    """
+
+    def __init__(self, backend: Any):
+        self._backend = backend
+
+    def get(self, provider: str, language: str, use_gpu: bool) -> Any:
+        """Get a TTS backend instance.
+
+        For PyQt, this returns the pre-initialized backend.
+        """
+        return self._backend
+
+    def dispose_all(self) -> None:
+        """Dispose all backend resources."""
+        pass  # PyQt manages backend lifecycle in thread
+
+
+class PyQtVoiceResolver:
+    """PyQt implementation of VoiceResolver protocol.
+
+    Wraps load_voice_cached from the ConversionThread.
+    """
+
+    def __init__(self, thread: Any):
+        self._thread = thread
+
+    def resolve(self, voice_spec: str) -> ResolvedVoice:
+        """Resolve a voice spec into a loaded voice."""
+        from abogen.domain.voice_resolution import resolve_fallback_voice_spec
+
+        # Use thread's load_voice_cached method
+        loaded_voice = self._thread.load_voice_cached(voice_spec, self._thread.backend)
+
+        return ResolvedVoice(
+            provider="kokoro",
+            resolved_spec=voice_spec,
+            voice=loaded_voice,
+            speed=self._thread.speed,
+            supertonic_steps=getattr(self._thread, "supertonic_total_steps", 5),
+        )
+
+
+def _level_to_color(level: str) -> str:
+    """Map log level to PyQt color string."""
+    colors = {
+        "info": "grey",
+        "warning": "orange",
+        "error": "red",
+        "debug": "grey",
+    }
+    return colors.get(level, "grey")

abogen/pyqt/gui.py

@@ -7,6 +7,7 @@ import base64
 import re
 from abogen.pyqt.queue_manager_gui import QueueManager
 from abogen.pyqt.queued_item import QueuedItem
+
 import abogen.hf_tracker as hf_tracker
 import hashlib  # Added for cache path generation
 from PyQt6.QtWidgets import (
@@ -69,10 +70,8 @@ from abogen.utils import (
     LoadPipelineThread,
 )
 
-from abogen.subtitle_utils import (
-    clean_text,
-    calculate_text_length,
-)
+from abogen.subtitle_utils import clean_text
+from abogen.domain.text_utils import calculate_text_length
 
 from abogen.pyqt.conversion import ConversionThread, VoicePreviewThread, PlayAudioThread, ChapterOptionsDialog, TimestampDetectionDialog
 from abogen.pyqt.book_handler import HandlerDialog
@@ -82,14 +81,18 @@ from abogen.constants import (
     GITHUB_URL,
     PROGRAM_DESCRIPTION,
     LANGUAGE_DESCRIPTIONS,
-    VOICES_INTERNAL,
     SUPPORTED_LANGUAGES_FOR_SUBTITLE_GENERATION,
     COLORS,
     SUBTITLE_FORMATS,
 )
+from abogen.tts_plugin.utils import get_voices
 import threading
 from abogen.pyqt.voice_formula_gui import VoiceFormulaDialog
 from abogen.voice_profiles import load_profiles
+from abogen.domain.settings_core import all_settings_defaults
+
+# Module-level default cache for use outside __init__
+_DEFAULTS = all_settings_defaults()
 
 # Import ctypes for Windows-specific taskbar icon
 if platform.system() == "Windows":
@@ -837,7 +840,7 @@ class WordSubstitutionsDialog(QDialog):
             self,
         )
         instructions.setStyleSheet(
-            "padding: 10px; background-color: #f0f0f0; border-radius: 5px;"
+            f"padding: 10px; background-color: {COLORS['GREY_BACKGROUND']}; border-radius: 5px;"
         )
         instructions.setWordWrap(True)
         layout.addWidget(instructions)
@@ -911,9 +914,10 @@ class abogen(QWidget):
     def __init__(self):
         super().__init__()
         self.config = load_config()
-        self.apply_theme(self.config.get("theme", "system"))
+        _d = all_settings_defaults()
+        self.apply_theme(self.config.get("theme", _d["theme"]))
         migrate_subtitle_format(self.config)
-        self.check_updates = self.config.get("check_updates", True)
+        self.check_updates = self.config.get("check_updates", _d["check_updates"])
         self.save_option = self.config.get("save_option", "Save next to input file")
         self.selected_output_folder = self.config.get("selected_output_folder", None)
         self.selected_file = self.selected_file_type = self.selected_book_path = None
@@ -921,7 +925,7 @@ class abogen(QWidget):
             None  # Add new variable to track the displayed file path
         )
         # Max log lines
-        self.log_window_max_lines = self.config.get("log_window_max_lines", 2000)
+        self.log_window_max_lines = self.config.get("log_window_max_lines", _d["log_window_max_lines"])
         self.selected_chapters = set()
         self.last_opened_book_path = None  # Track the last opened book path
         self.last_output_path = None
@@ -936,40 +940,28 @@ class abogen(QWidget):
             self.selected_voice = None
             self.selected_lang = None
         else:
-            self.selected_voice = self.config.get("selected_voice", "af_heart")
+            self.selected_voice = self.config.get("selected_voice", _d["selected_voice"])
             self.selected_lang = self.selected_voice[0] if self.selected_voice else None
         self.is_converting = False
-        self.subtitle_mode = self.config.get("subtitle_mode", "Sentence")
-        self.max_subtitle_words = self.config.get(
-            "max_subtitle_words", 50
-        )  # Default max words per subtitle
-        self.silence_duration = self.config.get(
-            "silence_duration", 2.0
-        )  # Default silence duration
-        self.selected_format = self.config.get("selected_format", "wav")
-        self.separate_chapters_format = self.config.get(
-            "separate_chapters_format", "wav"
-        )  # Format for individual chapter files
-        self.use_gpu = self.config.get(
-            "use_gpu", True  # Load GPU setting with default True
-        )
-        self.replace_single_newlines = self.config.get("replace_single_newlines", True)
-        self.use_silent_gaps = self.config.get("use_silent_gaps", True)
-        self.subtitle_speed_method = self.config.get("subtitle_speed_method", "tts")
-        self.use_spacy_segmentation = self.config.get("use_spacy_segmentation", True)
+        self.subtitle_mode = self.config.get("subtitle_mode", _d["subtitle_mode"])
+        self.max_subtitle_words = self.config.get("max_subtitle_words", _d["max_subtitle_words"])
+        self.silence_duration = self.config.get("silence_duration", _d.get("silence_between_chapters", 2.0))
+        self.selected_format = self.config.get("selected_format", _d["selected_format"])
+        self.separate_chapters_format = self.config.get("separate_chapters_format", _d["separate_chapters_format"])
+        self.use_gpu = self.config.get("use_gpu", _d["use_gpu"])
+        self.replace_single_newlines = self.config.get("replace_single_newlines", _d.get("replace_single_newlines", True))
+        self.use_silent_gaps = self.config.get("use_silent_gaps", _d["use_silent_gaps"])
+        self.subtitle_speed_method = self.config.get("subtitle_speed_method", _d["subtitle_speed_method"])
+        self.use_spacy_segmentation = self.config.get("use_spacy_segmentation", _d["use_spacy_segmentation"])
+        self.read_title_intro = self.config.get("read_title_intro", _d.get("read_title_intro", False))
+        self.read_closing_outro = self.config.get("read_closing_outro", _d.get("read_closing_outro", True))
         # Word substitution settings
-        self.word_substitutions_enabled = self.config.get(
-            "word_substitutions_enabled", False
-        )
-        self.word_substitutions_list = self.config.get("word_substitutions_list", "")
-        self.case_sensitive_substitutions = self.config.get(
-            "case_sensitive_substitutions", False
-        )
-        self.replace_all_caps = self.config.get("replace_all_caps", False)
-        self.replace_numerals = self.config.get("replace_numerals", False)
-        self.fix_nonstandard_punctuation = self.config.get(
-            "fix_nonstandard_punctuation", False
-        )
+        self.word_substitutions_enabled = self.config.get("word_substitutions_enabled", _d["word_substitutions_enabled"])
+        self.word_substitutions_list = self.config.get("word_substitutions_list", _d["word_substitutions_list"])
+        self.case_sensitive_substitutions = self.config.get("case_sensitive_substitutions", _d["case_sensitive_substitutions"])
+        self.replace_all_caps = self.config.get("replace_all_caps", _d["replace_all_caps"])
+        self.replace_numerals = self.config.get("replace_numerals", _d["replace_numerals"])
+        self.fix_nonstandard_punctuation = self.config.get("fix_nonstandard_punctuation", _d["fix_nonstandard_punctuation"])
         self._pending_close_event = None
         self.gpu_ok = False  # Initialize GPU availability status
 
@@ -997,7 +989,7 @@ class abogen(QWidget):
         self.current_queue_index = 0
 
         self.initUI()
-        self.speed_slider.setValue(int(self.config.get("speed", 1.00) * 100))
+        self.speed_slider.setValue(int(self.config.get("speed", _d["speed"]) * 100))
         self.update_speed_label()
         # Set initial selection: prefer profile, else voice
         idx = -1
@@ -1873,7 +1865,7 @@ class abogen(QWidget):
         for pname in load_profiles().keys():
             self.voice_combo.addItem(profile_icon, pname, f"profile:{pname}")
         # re-add voices
-        for v in VOICES_INTERNAL:
+        for v in get_voices("kokoro"):
             icon = QIcon()
             flag_path = get_resource_path("abogen.assets.flags", f"{v[0]}.png")
             if flag_path and os.path.exists(flag_path):
@@ -2160,7 +2152,7 @@ class abogen(QWidget):
             )
 
             # CHECK GLOBAL OVERRIDE SETTING
-            if not self.config.get("queue_override_settings", False):
+            if not self.config.get("queue_override_settings", _DEFAULTS["queue_override_settings"]):
                 self.selected_lang = queued_item.lang_code
                 self.speed_slider.setValue(int(queued_item.speed * 100))
                 
@@ -2234,11 +2226,10 @@ class abogen(QWidget):
             self.current_queue_index = 0  # Reset for next time
 
     def get_voice_formula(self) -> str:
+        from abogen.voice_formulas import pairs_to_formula
+
         if self.mixed_voice_state:
-            formula_components = [
-                f"{name}*{weight}" for name, weight in self.mixed_voice_state
-            ]
-            return " + ".join(filter(None, formula_components))
+            return pairs_to_formula(self.mixed_voice_state) or ""
         else:
             return self.selected_voice
 
@@ -2316,9 +2307,9 @@ class abogen(QWidget):
             file_size_str = "Unknown"
 
         # pipeline_loaded_callback remains unchanged
-        def pipeline_loaded_callback(np_module, kpipeline_class, error):
+        def pipeline_loaded_callback(backend, error):
             if error:
-                self.update_log((f"Error loading numpy or KPipeline: {error}", "red"))
+                self.update_log((f"Error loading TTS backend: {error}", "red"))
                 prevent_sleep_end()
                 return
 
@@ -2341,8 +2332,7 @@ class abogen(QWidget):
                 self.selected_output_folder,
                 subtitle_mode=actual_subtitle_mode,
                 output_format=self.selected_format,
-                np_module=np_module,
-                kpipeline_class=kpipeline_class,
+                backend=backend,
                 start_time=self.start_time,
                 total_char_count=self.char_count,
                 use_gpu=self.gpu_ok,
@@ -2403,6 +2393,9 @@ class abogen(QWidget):
                 self.conversion_thread.merge_chapters_at_end = getattr(
                     self, "merge_chapters_at_end", True
                 )
+            # Pass intro/outro settings
+            self.conversion_thread.read_title_intro = self.read_title_intro
+            self.conversion_thread.read_closing_outro = self.read_closing_outro
             self.conversion_thread.progress_updated.connect(self.update_progress)
             self.conversion_thread.log_updated.connect(self.update_log)
             self.conversion_thread.conversion_finished.connect(
@@ -2426,7 +2419,11 @@ class abogen(QWidget):
             self.gpu_ok = gpu_ok
             self.update_log((gpu_msg, gpu_ok))
             self.update_log("Loading modules...")
-            load_thread = LoadPipelineThread(pipeline_loaded_callback)
+
+            lang_code = self.selected_lang or "a"
+            load_thread = LoadPipelineThread(
+                pipeline_loaded_callback, lang_code=lang_code, use_gpu=gpu_ok
+            )
             load_thread.start()
 
         threading.Thread(target=gpu_and_load, daemon=True).start()
@@ -2437,7 +2434,7 @@ class abogen(QWidget):
             return
 
         # Check if override was active (this determines which settings were ACTUALLY used)
-        override_active = self.config.get("queue_override_settings", False)
+        override_active = self.config.get("queue_override_settings", _DEFAULTS["queue_override_settings"])
 
         # If override is ON, capture the global settings that were used for processing
         if override_active:
@@ -2863,18 +2860,18 @@ class abogen(QWidget):
             )
             self.loading_movie.start()
 
-        def pipeline_loaded_callback(np_module, kpipeline_class, error):
-            self._on_pipeline_loaded_for_preview(np_module, kpipeline_class, error)
-
-        load_thread = LoadPipelineThread(pipeline_loaded_callback)
+        lang = self.selected_lang or "a"
+        load_thread = LoadPipelineThread(
+            self._on_pipeline_loaded_for_preview, lang_code=lang, use_gpu=self.gpu_ok
+        )
         load_thread.start()
 
-    def _on_pipeline_loaded_for_preview(self, np_module, kpipeline_class, error):
+    def _on_pipeline_loaded_for_preview(self, backend, error):
         # stop loading animation and restore icon on error
         if error:
             self.loading_movie.stop()
             self._show_error_message_box(
-                "Loading Error", f"Error loading numpy or KPipeline: {error}"
+                "Loading Error", f"Error loading TTS backend: {error}"
             )
             self.btn_preview.setIcon(self.play_icon)
             self.btn_preview.setEnabled(True)
@@ -2912,7 +2909,7 @@ class abogen(QWidget):
         gpu_msg, gpu_ok = get_gpu_acceleration(self.use_gpu)
 
         self.preview_thread = VoicePreviewThread(
-            np_module, kpipeline_class, lang, voice, speed, gpu_ok
+            backend, lang, voice, speed, gpu_ok
         )
         self.preview_thread.finished.connect(self._play_preview_audio)
         self.preview_thread.error.connect(self._preview_error)
@@ -3215,12 +3212,16 @@ class abogen(QWidget):
             )
             box.setDefaultButton(QMessageBox.StandardButton.No)
             if box.exec() == QMessageBox.StandardButton.Yes:
+                from abogen import shutdown
+                shutdown.request_shutdown()
                 self.cleanup_conversion_thread()
                 self.cleanup_preview_threads()
                 event.accept()
             else:
                 event.ignore()
         else:
+            from abogen import shutdown
+            shutdown.request_shutdown()
             self.cleanup_conversion_thread()
             self.cleanup_preview_threads()
             event.accept()
@@ -3409,7 +3410,7 @@ class abogen(QWidget):
         app.installEventFilter(app._dark_titlebar_event_filter)
 
         # Save config if changed
-        if self.config.get("theme", "system") != theme:
+        if self.config.get("theme", _DEFAULTS["theme"]) != theme:
             self.config["theme"] = theme
             save_config(self.config)
 
@@ -3431,7 +3432,7 @@ class abogen(QWidget):
         ]
 
         # Get current theme from config, default to "system"
-        current_theme = self.config.get("theme", "system")
+        current_theme = self.config.get("theme", _DEFAULTS["theme"])
         for value, text in theme_options:
             theme_action = QAction(text, self)
             theme_action.setCheckable(True)
@@ -3562,6 +3563,27 @@ class abogen(QWidget):
         # Add separator
         menu.addSeparator()
 
+        # Add title intro option
+        self.title_intro_action = QAction("Read title intro before first chapter", self)
+        self.title_intro_action.setCheckable(True)
+        self.title_intro_action.setChecked(self.read_title_intro)
+        self.title_intro_action.triggered.connect(
+            lambda checked: self.toggle_read_title_intro(checked)
+        )
+        menu.addAction(self.title_intro_action)
+
+        # Add closing outro option
+        self.closing_outro_action = QAction("Read closing outro after last chapter", self)
+        self.closing_outro_action.setCheckable(True)
+        self.closing_outro_action.setChecked(self.read_closing_outro)
+        self.closing_outro_action.triggered.connect(
+            lambda checked: self.toggle_read_closing_outro(checked)
+        )
+        menu.addAction(self.closing_outro_action)
+
+        # Add separator
+        menu.addSeparator()
+
         # Add "Pre-download models and voices for offline use" option
         predownload_action = QAction(
             "Pre-download models and voices for offline use", self
@@ -3573,7 +3595,7 @@ class abogen(QWidget):
         disable_kokoro_action = QAction("Disable Kokoro's internet access", self)
         disable_kokoro_action.setCheckable(True)
         disable_kokoro_action.setChecked(
-            self.config.get("disable_kokoro_internet", False)
+            self.config.get("disable_kokoro_internet", _DEFAULTS["disable_kokoro_internet"])
         )
         disable_kokoro_action.triggered.connect(
             lambda checked: self.toggle_kokoro_internet_access(checked)
@@ -3583,7 +3605,7 @@ class abogen(QWidget):
         # Add check for updates option
         check_updates_action = QAction("Check for updates at startup", self)
         check_updates_action.setCheckable(True)
-        check_updates_action.setChecked(self.config.get("check_updates", True))
+        check_updates_action.setChecked(self.config.get("check_updates", _DEFAULTS["check_updates"]))
         check_updates_action.triggered.connect(self.toggle_check_updates)
         menu.addAction(check_updates_action)
 
@@ -3638,6 +3660,16 @@ class abogen(QWidget):
         self.config["use_spacy_segmentation"] = enabled
         save_config(self.config)
 
+    def toggle_read_title_intro(self, enabled):
+        self.read_title_intro = enabled
+        self.config["read_title_intro"] = enabled
+        save_config(self.config)
+
+    def toggle_read_closing_outro(self, enabled):
+        self.read_closing_outro = enabled
+        self.config["read_closing_outro"] = enabled
+        save_config(self.config)
+
     def restart_app(self):
 
         import sys
@@ -4209,7 +4241,7 @@ Categories=AudioVideo;Audio;Utility;
         """Open a dialog to set the maximum words per subtitle"""
         from PyQt6.QtWidgets import QInputDialog
 
-        current_value = self.config.get("max_subtitle_words", 50)
+        current_value = self.config.get("max_subtitle_words", _DEFAULTS["max_subtitle_words"])
 
         value, ok = QInputDialog.getInt(
             self,
@@ -4237,7 +4269,7 @@ Categories=AudioVideo;Audio;Utility;
     def set_silence_between_chapters(self):
         """Open a dialog to set the silence duration between chapters"""
 
-        current_value = self.config.get("silence_duration", 2.0)
+        current_value = self.config.get("silence_duration", _DEFAULTS.get("silence_between_chapters", 2.0))
 
         dlg = QInputDialog(self)
         dlg.setWindowTitle("Silence Duration (seconds)")

abogen/pyqt/main.py

@@ -1,10 +1,10 @@
 import os
 import sys
 import platform
-import atexit
-import signal
-from abogen.utils import get_resource_path, load_config, prevent_sleep_end
 
+# Initialise global shutdown handling (atexit, signals, Qt) as early as possible.
+from abogen import shutdown  # noqa: F401
+shutdown.register_shutdown()
 
 # Fix PyTorch DLL loading issue ([WinError 1114]) on Windows before importing PyQt6
 if platform.system() == "Windows":
@@ -46,6 +46,8 @@ except ImportError:
     print("PyQt6 not installed.")
 
 
+from abogen.utils import get_resource_path
+
 # Pre-load "libxcb-cursor" on Linux (fixes #101)
 if platform.system() == "Linux":
     arch = platform.machine().lower()
@@ -94,6 +96,7 @@ os.environ["HF_HUB_DISABLE_TELEMETRY"] = "1"  # Disable Hugging Face telemetry
 os.environ["HF_HUB_ETAG_TIMEOUT"] = "10"  # Metadata request timeout (seconds)
 os.environ["HF_HUB_DOWNLOAD_TIMEOUT"] = "10"  # File download timeout (seconds)
 os.environ["HF_HUB_DISABLE_SYMLINKS_WARNING"] = "1"  # Disable symlinks warning
+from abogen.utils import load_config
 if load_config().get("disable_kokoro_internet", False):
     print("INFO: Kokoro's internet access is disabled.")
     os.environ["HF_HUB_OFFLINE"] = "1"  # Disable Hugging Face Hub internet access
@@ -105,25 +108,6 @@ from abogen.constants import PROGRAM_NAME, VERSION
 os.environ["MIOPEN_FIND_MODE"] = "FAST"
 os.environ["MIOPEN_CONV_PRECISE_ROCM_TUNING"] = "0"
 
-# Reset sleep states
-atexit.register(prevent_sleep_end)
-
-
-# Also handle signals (Ctrl+C, kill, etc.)
-def _cleanup_sleep(signum, frame):
-    prevent_sleep_end()
-    sys.exit(0)
-
-
-signal.signal(signal.SIGINT, _cleanup_sleep)
-signal.signal(signal.SIGTERM, _cleanup_sleep)
-
-# Ensure sys.stdout and sys.stderr are valid in GUI mode
-if sys.stdout is None:
-    sys.stdout = open(os.devnull, "w")
-if sys.stderr is None:
-    sys.stderr = open(os.devnull, "w")
-
 # Enable MPS GPU acceleration on Mac Apple Silicon
 if platform.system() == "Darwin" and platform.processor() == "arm":
     os.environ["PYTORCH_ENABLE_MPS_FALLBACK"] = "1"
@@ -136,6 +120,8 @@ def qt_message_handler(mode, context, message):
         return  # Suppress this specific message
     if "setGrabPopup called with a parent, QtWaylandClient" in message:
         return
+    if "Failed to register with host portal" in message:
+        return
 
     if mode == QtMsgType.QtWarningMsg:
         print(f"Qt Warning: {message}")

abogen/pyqt/predownload_gui.py

@@ -21,7 +21,8 @@ from PyQt6.QtWidgets import (
 )
 from PyQt6.QtCore import QThread, pyqtSignal
 
-from abogen.constants import COLORS, VOICES_INTERNAL
+from abogen.constants import COLORS
+from abogen.tts_plugin.utils import get_voices
 from abogen.spacy_utils import SPACY_MODELS
 import abogen.hf_tracker
 
@@ -114,7 +115,7 @@ class PreDownloadWorker(QThread):
             self._voices_success = False
             return
 
-        voice_list = VOICES_INTERNAL
+        voice_list = get_voices("kokoro")
         for idx, voice in enumerate(voice_list, start=1):
             if self._cancelled:
                 self._voices_success = False
@@ -462,14 +463,14 @@ class PreDownloadDialog(QDialog):
         try:
             from huggingface_hub import try_to_load_from_cache
 
-            for voice in VOICES_INTERNAL:
+            for voice in get_voices("kokoro"):
                 if not try_to_load_from_cache(
                     repo_id="hexgrad/Kokoro-82M", filename=f"voices/{voice}.pt"
                 ):
                     missing.append(voice)
         except Exception:
             # If HF missing, report all as missing
-            return False, list(VOICES_INTERNAL)
+            return False, list(get_voices("kokoro"))
         return (len(missing) == 0), missing
 
     def _check_kokoro_model(self) -> bool:

abogen/pyqt/queue_manager_gui.py

@@ -523,7 +523,7 @@ class QueueManager(QDialog):
         return attrs
 
     def add_files_from_paths(self, file_paths):
-        from abogen.subtitle_utils import calculate_text_length
+        from abogen.domain.text_utils import calculate_text_length
         from PyQt6.QtWidgets import QMessageBox
         import os
 

abogen/pyqt/voice_formula_gui.py

@@ -28,11 +28,11 @@ from PyQt6.QtWidgets import (
 from PyQt6.QtCore import Qt, QTimer, QPoint, QRect, QSize
 from PyQt6.QtGui import QPixmap, QIcon, QAction
 from abogen.constants import (
-    VOICES_INTERNAL,
     SUPPORTED_LANGUAGES_FOR_SUBTITLE_GENERATION,
     LANGUAGE_DESCRIPTIONS,
     COLORS,
 )
+from abogen.tts_plugin.utils import get_voices
 import re
 import platform
 from abogen.utils import get_resource_path
@@ -179,7 +179,7 @@ class VoiceMixer(QWidget):
         layout.addWidget(QLabel(name), alignment=Qt.AlignmentFlag.AlignCenter)
 
         # Voice name label with gender icon
-        is_female = self.voice_name in VOICES_INTERNAL and self.voice_name[1] == "f"
+        is_female = self.voice_name in get_voices("kokoro") and self.voice_name[1] == "f"
 
         # Icons layout (flag and gender)
         icons_layout = QHBoxLayout()
@@ -772,7 +772,7 @@ class VoiceFormulaDialog(QDialog):
 
     def add_voices(self, initial_state):
         first_enabled_voice = None
-        for voice in VOICES_INTERNAL:
+        for voice in get_voices("kokoro"):
             language_code = voice[0]  # First character is the language code
             matching_voice = next(
                 (item for item in initial_state if item[0] == voice), None

abogen/shutdown.py

@@ -0,0 +1,144 @@
+"""Graceful shutdown — process-level hooks and orchestration.
+
+Responsibilities:
+- Install atexit/signal/Qt hooks
+- Stop WebUI ConversionService (worker thread)
+- Restore sleep prevention
+- Terminate child processes (ffmpeg, etc.)
+- Delegate GPU/engine/UI cleanup to application.cleanup
+
+App-layer cleanup (GPU, engines, UI callbacks) lives in application/cleanup.py.
+Per-conversion cleanup lives in run_conversion() finally block.
+"""
+
+from __future__ import annotations
+
+import atexit
+import signal
+import sys
+from typing import Callable
+
+_CLEANUP_FUNCS: list[Callable[[], None]] = []
+_EXECUTED = False
+
+
+def register_cleanup(fn: Callable[[], None]) -> None:
+    """Register a cleanup function to run on shutdown."""
+    _CLEANUP_FUNCS.append(fn)
+
+
+def _run_cleanups() -> None:
+    global _EXECUTED
+    if _EXECUTED:
+        return
+    _EXECUTED = True
+    for fn in _CLEANUP_FUNCS:
+        try:
+            fn()
+        except Exception:
+            pass
+
+
+# ---- Process-level cleanup functions ----
+
+
+def _stop_conversion_service() -> None:
+    """Stop WebUI ConversionService worker thread."""
+    try:
+        from abogen.webui.service import get_service
+        svc = get_service()
+        if svc is not None:
+            svc.shutdown()
+    except Exception:
+        pass
+
+
+def _restore_sleep() -> None:
+    """Restore system sleep prevention (caffeinate/systemd-inhibit/Windows)."""
+    try:
+        from abogen.utils import prevent_sleep_end
+        prevent_sleep_end()
+    except Exception:
+        pass
+
+
+def _terminate_subprocesses() -> None:
+    """Terminate all child processes (ffmpeg, etc.)."""
+    try:
+        import psutil
+    except Exception:
+        return
+
+    try:
+        current = psutil.Process()
+        for child in current.children(recursive=True):
+            try:
+                child.terminate()
+            except Exception:
+                pass
+        gone, alive = psutil.wait_procs(current.children(recursive=True), timeout=3)
+        for proc in alive:
+            try:
+                proc.kill()
+            except Exception:
+                pass
+    except Exception:
+        pass
+
+
+def _app_cleanup() -> None:
+    """Delegate to application-layer cleanup (engines, GPU, UI callbacks)."""
+    try:
+        from abogen.application.cleanup import cleanup
+        cleanup()
+    except Exception:
+        pass
+
+
+# Register in execution order
+register_cleanup(_stop_conversion_service)
+register_cleanup(_app_cleanup)
+register_cleanup(_restore_sleep)
+register_cleanup(_terminate_subprocesses)
+
+
+def register_shutdown() -> None:
+    """Install process-wide shutdown hooks (atexit, signals, Qt)."""
+    if register_shutdown._registered:
+        return
+    register_shutdown._registered = True
+
+    atexit.register(_run_cleanups)
+
+    # POSIX signals
+    for sig in (signal.SIGINT, signal.SIGTERM):
+        try:
+            signal.signal(sig, _on_signal)
+        except Exception:
+            pass
+
+    # Qt hook — connect AFTER QApplication is created
+    try:
+        from PyQt6.QtWidgets import QApplication
+
+        app = QApplication.instance()
+        if app is not None:
+            app.aboutToQuit.connect(_run_cleanups)
+    except Exception:
+        pass
+
+
+register_shutdown._registered = False
+
+
+def _on_signal(signum: int, _frame) -> None:
+    _run_cleanups()
+    sys.exit(0)
+
+
+def request_shutdown() -> None:
+    """Programmatically trigger cleanup (e.g., from GUI closeEvent)."""
+    _run_cleanups()
+
+
+__all__ = ["register_shutdown", "request_shutdown", "register_cleanup"]

abogen/spacy_utils.py

@@ -2,24 +2,25 @@
 Lazy-loaded spaCy utilities for sentence segmentation.
 """
 
+from abogen.domain.enums import Language
+
 # Cached spaCy module and models (lazy loaded)
 _spacy = None
 _nlp_cache = {}
 
 # Language code to spaCy model mapping
 SPACY_MODELS = {
-    "a": "en_core_web_sm",  # American English
-    "b": "en_core_web_sm",  # British English
-    "e": "es_core_news_sm",  # Spanish
-    "f": "fr_core_news_sm",  # French
-    "i": "it_core_news_sm",  # Italian
-    "p": "pt_core_news_sm",  # Brazilian Portuguese
-    "z": "zh_core_web_sm",  # Mandarin Chinese
-    "j": "ja_core_news_sm",  # Japanese
-    "h": "xx_sent_ud_sm",  # Hindi (multi-language model)
+    Language.EN_US: "en_core_web_sm",
+    Language.EN_GB: "en_core_web_sm",
+    Language.ES: "es_core_news_sm",
+    Language.FR: "fr_core_news_sm",
+    Language.IT: "it_core_news_sm",
+    Language.PT_BR: "pt_core_news_sm",
+    Language.ZH: "zh_core_web_sm",
+    Language.JA: "ja_core_news_sm",
+    Language.HI: "xx_sent_ud_sm",
 }
 
-
 def _load_spacy():
     """Lazy load spaCy module."""
     global _spacy
@@ -33,13 +34,12 @@ def _load_spacy():
     return _spacy
 
 
-def get_spacy_model(lang_code, log_callback=None):
+def get_spacy_model(language: Language, log_callback=None):
     """
-    Get or load a spaCy model for the given language code.
-    Downloads the model automatically if not available.
+    Get or load a spaCy model for the given language.
 
     Args:
-        lang_code: Language code (a, b, e, f, etc.)
+        language: Language enum value.
         log_callback: Optional function to log messages
 
     Returns:
@@ -47,25 +47,24 @@ def get_spacy_model(lang_code, log_callback=None):
     """
 
     def log(msg, is_error=False):
-        # Prefer GUI log callback when provided to avoid spamming stdout.
         if log_callback:
             color = "red" if is_error else "grey"
             try:
                 log_callback((msg, color))
             except Exception:
-                # Fallback to printing if callback misbehaves
                 print(msg)
         else:
             print(msg)
 
-    # Check if model is cached
-    if lang_code in _nlp_cache:
-        return _nlp_cache[lang_code]
+    if not isinstance(language, Language):
+        raise TypeError(f"language must be Language enum, got {type(language).__name__}: {language!r}")
 
-    # Check if language is supported
-    model_name = SPACY_MODELS.get(lang_code)
+    if language in _nlp_cache:
+        return _nlp_cache[language]
+
+    model_name = SPACY_MODELS.get(language)
     if not model_name:
-        log(f"\nspaCy: No model mapping for language '{lang_code}'...")
+        log(f"\nspaCy: No model mapping for language '{language}'...")
         return None
 
     # Lazy load spaCy
@@ -89,7 +88,7 @@ def get_spacy_model(lang_code, log_callback=None):
         if "parser" not in nlp.pipe_names and "sentencizer" not in nlp.pipe_names:
             nlp.add_pipe("sentencizer")
 
-        _nlp_cache[lang_code] = nlp
+        _nlp_cache[language] = nlp
         return nlp
     except OSError:
         # Model not found, attempt download
@@ -106,7 +105,7 @@ def get_spacy_model(lang_code, log_callback=None):
             if "parser" not in nlp.pipe_names and "sentencizer" not in nlp.pipe_names:
                 nlp.add_pipe("sentencizer")
 
-            _nlp_cache[lang_code] = nlp
+            _nlp_cache[language] = nlp
             log(f"spaCy model '{model_name}' downloaded and loaded")
             return nlp
         except Exception as e:
@@ -120,19 +119,19 @@ def get_spacy_model(lang_code, log_callback=None):
         return None
 
 
-def segment_sentences(text, lang_code, log_callback=None):
+def segment_sentences(text, language: Language, log_callback=None):
     """
     Segment text into sentences using spaCy.
 
     Args:
         text: Text to segment
-        lang_code: Language code
+        language: Language enum value
         log_callback: Optional function to log messages
 
     Returns:
         List of sentence strings, or None if spaCy unavailable
     """
-    nlp = get_spacy_model(lang_code, log_callback)
+    nlp = get_spacy_model(language, log_callback)
     if nlp is None:
         return None
 

abogen/speaker_configs.py

@@ -4,7 +4,7 @@ import json
 import os
 from typing import Any, Dict, List, Optional
 
-from abogen.constants import LANGUAGE_DESCRIPTIONS
+from abogen.constants import KOKORO_CODE_LABELS
 from abogen.utils import get_user_config_path
 
 _CONFIG_WRAPPER_KEY = "abogen_speaker_configs"
@@ -163,4 +163,4 @@ def list_configs() -> List[Dict[str, Any]]:
 
 def describe_language(code: str) -> str:
     code = (code or "a").lower()
-    return LANGUAGE_DESCRIPTIONS.get(code, code.upper())
+    return KOKORO_CODE_LABELS.get(code, code.upper())

abogen/subtitle_utils.py

@@ -1,7 +1,7 @@
 import re
-import platform
 from abogen.utils import detect_encoding, load_config
 from abogen.constants import SAMPLE_VOICE_TEXTS
+from abogen.domain.enums import Language
 
 # Pre-compile frequently used regex patterns for better performance
 _METADATA_TAG_PATTERN = re.compile(r"<<METADATA_[^:]+:[^>]*>>")
@@ -23,13 +23,6 @@ _VTT_NOTE_PATTERN = re.compile(r"NOTE\s*\n.*?(?=\n\n|$)", re.DOTALL)
 _DOUBLE_NEWLINE_SPLIT_PATTERN = re.compile(r"\n\s*\n")
 _VTT_TIMESTAMP_PATTERN = re.compile(r"([\d:.]+)\s*-->\s*([\d:.]+)")
 _TIMESTAMP_ONLY_PATTERN = re.compile(r"^(\d{1,2}:\d{2}:\d{2}(?:[.,]\d{1,3})?)$")
-_WINDOWS_ILLEGAL_CHARS_PATTERN = re.compile(r'[<>:"/\\|?*]')
-_CONTROL_CHARS_PATTERN = re.compile(r"[\x00-\x1f]")
-_LINUX_CONTROL_CHARS_PATTERN = re.compile(
-    r"[\x01-\x1f]"
-)  # Linux: exclude \x00 for separate handling
-_MACOS_ILLEGAL_CHARS_PATTERN = re.compile(r"[:]")
-_LINUX_ILLEGAL_CHARS_PATTERN = re.compile(r"[/\x00]")
 
 
 def clean_subtitle_text(text):
@@ -41,17 +34,6 @@ def clean_subtitle_text(text):
     return text.strip()
 
 
-def calculate_text_length(text):
-    # Use pre-compiled patterns for better performance
-    # Ignore chapter markers, voice markers, and metadata patterns in a single pass
-    text = _CHAPTER_MARKER_PATTERN.sub("", text)
-    text = _VOICE_MARKER_PATTERN.sub("", text)
-    text = _METADATA_TAG_PATTERN.sub("", text)
-    # Ignore newlines and leading/trailing spaces
-    text = text.replace("\n", "").strip()
-    # Calculate character count
-    char_count = len(text)
-    return char_count
 
 
 def clean_text(text, *args, **kwargs):
@@ -396,189 +378,27 @@ def parse_ass_file(file_path):
     return subtitles
 
 
-def get_sample_voice_text(lang_code):
-    return SAMPLE_VOICE_TEXTS.get(lang_code, SAMPLE_VOICE_TEXTS["a"])
-
-
-def sanitize_name_for_os(name, is_folder=True):
-    """
-    Sanitize a filename or folder name based on the operating system.
+def get_sample_voice_text(language):
+    """Get sample voice text for a language.
 
     Args:
-        name: The name to sanitize
-        is_folder: Whether this is a folder name (default: True)
-
-    Returns:
-        Sanitized name safe for the current OS
+        language: Language enum value or string (for backward compatibility).
     """
-    if not name:
-        return "audiobook"
+    if isinstance(language, str):
+        try:
+            language = Language.from_str(language)
+        except (ValueError, AttributeError):
+            language = Language.EN_US
+    return SAMPLE_VOICE_TEXTS.get(language, SAMPLE_VOICE_TEXTS[Language.EN_US])
 
-    system = platform.system()
 
-    if system == "Windows":
-        # Windows illegal characters: < > : " / \ | ? *
-        # Also can't end with space or dot
-        # Use pre-compiled pattern for better performance
-        sanitized = _WINDOWS_ILLEGAL_CHARS_PATTERN.sub("_", name)
-        # Remove control characters (0-31)
-        sanitized = _CONTROL_CHARS_PATTERN.sub("_", sanitized)
-        # Remove trailing spaces and dots
-        sanitized = sanitized.rstrip(". ")
-        # Windows reserved names (CON, PRN, AUX, NUL, COM1-9, LPT1-9)
-        reserved = (
-            ["CON", "PRN", "AUX", "NUL"]
-            + [f"COM{i}" for i in range(1, 10)]
-            + [f"LPT{i}" for i in range(1, 10)]
+# Backward-compatible re-exports — canonical location is domain/output_paths.py
+from abogen.domain.output_paths import sanitize_name_for_os  # noqa: E402, F401
+
+# Backward-compatible re-exports — canonical location is domain/voice_markers.py
+from abogen.domain.voice_markers import (  # noqa: E402, F401
+    validate_voice_name,
+    split_text_by_voice_markers,
+    _VOICE_MARKER_PATTERN,
+    _VOICE_MARKER_SEARCH_PATTERN,
 )
-        if sanitized.upper() in reserved or sanitized.upper().split(".")[0] in reserved:
-            sanitized = f"_{sanitized}"
-    elif system == "Darwin":  # macOS
-        # macOS illegal characters: : (colon is converted to / by the system)
-        # Also can't start with dot (hidden file) for folders typically
-        # Use pre-compiled pattern for better performance
-        sanitized = _MACOS_ILLEGAL_CHARS_PATTERN.sub("_", name)
-        # Remove control characters
-        sanitized = _CONTROL_CHARS_PATTERN.sub("_", sanitized)
-        # Avoid leading dot for folders (creates hidden folders)
-        if is_folder and sanitized.startswith("."):
-            sanitized = "_" + sanitized[1:]
-    else:  # Linux and others
-        # Linux illegal characters: / and null character
-        # Though / is illegal, most other chars are technically allowed
-        # Use pre-compiled pattern for better performance
-        sanitized = _LINUX_ILLEGAL_CHARS_PATTERN.sub("_", name)
-        # Remove other control characters for safety (excluding \x00 which is already handled)
-        sanitized = _LINUX_CONTROL_CHARS_PATTERN.sub("_", sanitized)
-        # Avoid leading dot for folders (creates hidden folders)
-        if is_folder and sanitized.startswith("."):
-            sanitized = "_" + sanitized[1:]
-
-    # Ensure the name is not empty after sanitization
-    if not sanitized or sanitized.strip() == "":
-        sanitized = "audiobook"
-
-    # Limit length to 255 characters (common limit across filesystems)
-    if len(sanitized) > 255:
-        sanitized = sanitized[:255].rstrip(". ")
-
-    return sanitized
-
-
-def validate_voice_name(voice_name):
-    """Validate voice name against VOICES_INTERNAL list (case-insensitive).
-    Handles both single voices and formulas like 'af_heart*0.5 + am_echo*0.5'.
-
-    Args:
-        voice_name: Voice name or formula string to validate
-
-    Returns:
-        Tuple of (is_valid, invalid_voice_name):
-            - is_valid: True if all voices in the name/formula are valid
-            - invalid_voice_name: The first invalid voice found, or None if all valid
-    """
-    from abogen.constants import VOICES_INTERNAL
-
-    # Create case-insensitive lookup set (done once per call)
-    voice_lookup_lower = {v.lower() for v in VOICES_INTERNAL}
-    voice_name = voice_name.strip()
-
-    # Check if it's a formula (contains *)
-    if "*" in voice_name:
-        # Extract voice names from formula
-        voices = voice_name.split("+")
-        for term in voices:
-            if "*" in term:
-                base_voice = term.split("*")[0].strip()
-                # Case-insensitive comparison
-                if base_voice.lower() not in voice_lookup_lower:
-                    return False, base_voice
-        return True, None
-    else:
-        # Single voice - case-insensitive comparison
-        if voice_name.lower() not in voice_lookup_lower:
-            return False, voice_name
-        return True, None
-
-
-def split_text_by_voice_markers(text, default_voice):
-    """Split text by voice markers, returning list of (voice, text) tuples.
-
-    IMPORTANT: Returns the last voice used so it can persist across chapters.
-    Voice names are normalized to lowercase to match VOICES_INTERNAL.
-
-    Args:
-        text: Text potentially containing <<VOICE:name>> markers
-        default_voice: Voice to use if no markers found or before first marker
-
-    Returns:
-        Tuple of (segments_list, last_voice_used, valid_count, invalid_count):
-            - segments_list: List of (voice_name, segment_text) tuples
-            - last_voice_used: The voice that should continue into next chapter
-            - valid_count: Number of valid voice markers processed
-            - invalid_count: Number of invalid voice markers skipped
-    """
-    from abogen.constants import VOICES_INTERNAL
-
-    voice_splits = list(_VOICE_MARKER_SEARCH_PATTERN.finditer(text))
-
-    if not voice_splits:
-        # No voice markers, return entire text with default voice
-        return [(default_voice, text)], default_voice, 0, 0
-
-    segments = []
-    current_voice = default_voice
-    valid_markers = 0
-    invalid_markers = 0
-
-    # Text before first marker uses default voice
-    first_start = voice_splits[0].start()
-    if first_start > 0:
-        intro_text = text[:first_start].strip()
-        if intro_text:
-            segments.append((current_voice, intro_text))
-
-    # Process each voice marker
-    for idx, match in enumerate(voice_splits):
-        voice_name = match.group(1).strip()
-        start = match.end()
-        end = voice_splits[idx + 1].start() if idx + 1 < len(voice_splits) else len(text)
-        segment_text = text[start:end].strip()
-
-        # Validate voice name
-        is_valid, invalid_voice = validate_voice_name(voice_name)
-        if is_valid:
-            # Normalize to lowercase to match canonical form
-            # Handle both single voices and formulas
-            if "*" in voice_name:
-                # Normalize each voice in the formula
-                normalized_parts = []
-                for part in voice_name.split("+"):
-                    part = part.strip()
-                    if "*" in part:
-                        voice_part, weight = part.split("*", 1)
-                        # Find the canonical (lowercase) voice name
-                        voice_part_lower = voice_part.strip().lower()
-                        canonical_voice = next(
-                            (v for v in VOICES_INTERNAL if v.lower() == voice_part_lower),
-                            voice_part.strip()
-                        )
-                        normalized_parts.append(f"{canonical_voice}*{weight.strip()}")
-                current_voice = " + ".join(normalized_parts)
-            else:
-                # Find the canonical (lowercase) voice name
-                voice_name_lower = voice_name.lower()
-                current_voice = next(
-                    (v for v in VOICES_INTERNAL if v.lower() == voice_name_lower),
-                    voice_name
-                )
-            valid_markers += 1
-        else:
-            # Invalid voice - stay with previous voice
-            invalid_markers += 1
-
-        if segment_text:
-            segments.append((current_voice, segment_text))
-
-    # Return segments, last voice, and counts
-    return segments, current_voice, valid_markers, invalid_markers

abogen/text_extractor.py

@@ -16,7 +16,8 @@ import markdown  # type: ignore[import]
 from bs4 import BeautifulSoup, NavigableString  # type: ignore[import]
 from ebooklib import epub  # type: ignore[import]
 
-from .utils import calculate_text_length, clean_text, detect_encoding
+from .utils import clean_text, detect_encoding
+from .domain.text_utils import calculate_text_length
 
 logger = logging.getLogger(__name__)
 

abogen/tts_plugin/__init__.py

@@ -0,0 +1,170 @@
+"""TTS Plugin Architecture - Public API.
+
+This package defines the frozen Plugin API for the TTS Plugin Architecture.
+All public interfaces are fully defined but contain no business logic.
+
+Public modules:
+- types: Core domain value objects (AudioFormat, Duration, VoiceSelection, etc.)
+- errors: Error hierarchy (EngineError and subtypes)
+- manifest: Plugin manifest types (PluginManifest, EngineManifest, etc.)
+- engine: Engine and EngineSession protocols
+- capabilities: Optional capability interfaces (VoiceLister, PreviewGenerator, etc.)
+- host_context: HostContext dataclass
+- plugin: Plugin contract (create_engine function signature)
+- loader: Plugin discovery and loading
+- plugin_manager: Plugin management and engine creation
+- utils: Direct utility functions (get_voices, create_pipeline, etc.)
+
+Usage:
+    from abogen.tts_plugin import (
+        # Types
+        AudioFormat,
+        Duration,
+        VoiceSelection,
+        ParameterValues,
+        SynthesisRequest,
+        SynthesizedAudio,
+        EngineConfig,
+        # Errors
+        EngineError,
+        ModelNotFoundError,
+        ModelLoadError,
+        NetworkError,
+        InvalidInputError,
+        ConfigurationError,
+        CancelledError,
+        InternalError,
+        # Manifest
+        PluginManifest,
+        EngineManifest,
+        VoiceSourceManifest,
+        VoiceManifest,
+        ParameterManifest,
+        AudioFormatManifest,
+        EnumOption,
+        RequirementManifest,
+        GpuRequirement,
+        ModelManifest,
+        # Engine
+        Engine,
+        EngineSession,
+        # Capabilities
+        VoiceLister,
+        PreviewGenerator,
+        StreamingSynthesizer,
+        CancelableSession,
+        # Host Context
+        HostContext,
+        HttpClient,
+        # Plugin Manager
+        get_plugin_manager,
+        reset_plugin_manager,
+        # Utils
+        get_voices,
+        get_default_voice,
+        is_plugin_registered,
+        resolve_voice_to_plugin,
+        create_pipeline,
+    )
+"""
+
+from abogen.tts_plugin.capabilities import (
+    CancelableSession,
+    PreviewGenerator,
+    StreamingSynthesizer,
+    VoiceLister,
+)
+from abogen.tts_plugin.engine import Engine, EngineSession
+from abogen.tts_plugin.errors import (
+    CancelledError,
+    ConfigurationError,
+    EngineError,
+    InternalError,
+    InvalidInputError,
+    ModelLoadError,
+    ModelNotFoundError,
+    NetworkError,
+)
+from abogen.tts_plugin.host_context import HttpClient, HostContext
+from abogen.tts_plugin.manifest import (
+    AudioFormatManifest,
+    EngineManifest,
+    EnumOption,
+    GpuRequirement,
+    ModelManifest,
+    ParameterManifest,
+    PluginManifest,
+    RequirementManifest,
+    VoiceManifest,
+    VoiceSourceManifest,
+)
+from abogen.tts_plugin.types import (
+    AudioFormat,
+    Duration,
+    EngineConfig,
+    ParameterValues,
+    SynthesisRequest,
+    SynthesizedAudio,
+    VoiceSelection,
+)
+
+# Plugin Manager and Utils
+from abogen.tts_plugin.plugin_manager import get_plugin_manager, reset_plugin_manager
+from abogen.tts_plugin.utils import (
+    create_pipeline,
+    get_default_voice,
+    get_voices,
+    is_plugin_registered,
+    resolve_voice_to_plugin,
+)
+
+__all__ = [
+    # Types
+    "AudioFormat",
+    "Duration",
+    "VoiceSelection",
+    "ParameterValues",
+    "SynthesisRequest",
+    "SynthesizedAudio",
+    "EngineConfig",
+    # Errors
+    "EngineError",
+    "ModelNotFoundError",
+    "ModelLoadError",
+    "NetworkError",
+    "InvalidInputError",
+    "ConfigurationError",
+    "CancelledError",
+    "InternalError",
+    # Manifest
+    "PluginManifest",
+    "EngineManifest",
+    "VoiceSourceManifest",
+    "VoiceManifest",
+    "ParameterManifest",
+    "AudioFormatManifest",
+    "EnumOption",
+    "RequirementManifest",
+    "GpuRequirement",
+    "ModelManifest",
+    # Engine
+    "Engine",
+    "EngineSession",
+    # Capabilities
+    "VoiceLister",
+    "PreviewGenerator",
+    "StreamingSynthesizer",
+    "CancelableSession",
+    # Host Context
+    "HostContext",
+    "HttpClient",
+    # Plugin Manager
+    "get_plugin_manager",
+    "reset_plugin_manager",
+    # Utils
+    "get_voices",
+    "get_default_voice",
+    "is_plugin_registered",
+    "resolve_voice_to_plugin",
+    "create_pipeline",
+]

abogen/tts_plugin/capabilities.py

@@ -0,0 +1,103 @@
+"""Capability interfaces for the TTS Plugin Architecture.
+
+This module defines optional capability interfaces that engines can implement.
+Capabilities are additive; implementing new capabilities doesn't break old plugins.
+"""
+
+from __future__ import annotations
+
+from typing import Iterator, Protocol, runtime_checkable
+
+from abogen.tts_plugin.manifest import VoiceManifest
+from abogen.tts_plugin.types import SynthesisRequest, SynthesizedAudio, VoiceSelection
+
+
+@runtime_checkable
+class VoiceLister(Protocol):
+    """Protocol for listing available voices.
+
+    Engines that support voice listing should implement this interface.
+    """
+
+    def listVoices(self, sourceId: str) -> list[VoiceManifest]:
+        """List available voices for a given source.
+
+        Args:
+            sourceId: The voice source identifier.
+
+        Returns:
+            List of VoiceManifest describing available voices.
+
+        Raises:
+            EngineError: On failure.
+        """
+        ...
+
+
+@runtime_checkable
+class PreviewGenerator(Protocol):
+    """Protocol for generating voice previews.
+
+    Engines that support voice preview should implement this interface.
+    """
+
+    def generatePreview(self, voice: VoiceSelection, text: str) -> SynthesizedAudio:
+        """Generate a preview audio for a voice.
+
+        Args:
+            voice: Voice selection for the preview.
+            text: Text to use for the preview.
+
+        Returns:
+            SynthesizedAudio with the preview audio data.
+
+        Raises:
+            EngineError: On failure.
+        """
+        ...
+
+
+@runtime_checkable
+class StreamingSynthesizer(Protocol):
+    """Protocol for streaming synthesis.
+
+    Optional capability of EngineSession, not Engine.
+    Engines that support streaming synthesis should implement this interface.
+    """
+
+    def synthesizeStream(self, request: SynthesisRequest) -> Iterator[bytes]:
+        """Synthesize audio in streaming mode.
+
+        Args:
+            request: The synthesis request.
+
+        Yields:
+            Audio chunks as they become available.
+
+        Raises:
+            CancelledError: If cancel() is called during iteration.
+            EngineError: On synthesis failure.
+        """
+        ...
+        # This is a generator function; implementation will use yield
+        yield b""  # pragma: no cover
+
+
+@runtime_checkable
+class CancelableSession(Protocol):
+    """Protocol for cancellation support.
+
+    Optional capability for engines that support cancellation.
+    cancel() causes synthesize() to raise CancelledError.
+    """
+
+    def cancel(self) -> None:
+        """Cancel in-progress synthesis.
+
+        After cancellation, synthesize() raises CancelledError.
+        The session remains usable after cancellation.
+
+        Raises:
+            EngineError: If called after dispose().
+        """
+        ...

abogen/tts_plugin/engine.py

@@ -0,0 +1,95 @@
+"""Engine interfaces for the TTS Plugin Architecture.
+
+This module defines the core Engine and EngineSession protocols.
+These are the primary interfaces that plugin implementations must satisfy.
+"""
+
+from __future__ import annotations
+
+from typing import Protocol, runtime_checkable
+
+from abogen.tts_plugin.types import SynthesisRequest, SynthesizedAudio
+
+
+@runtime_checkable
+class EngineSession(Protocol):
+    """Protocol for a session that owns mutable execution state.
+
+    An EngineSession is created by Engine.createSession() and owns
+    mutable execution state isolated from other concurrent work.
+    It is NOT thread-safe.
+
+    Lifecycle:
+        1. Created by Engine.createSession()
+        2. Used for synthesis via synthesize()
+        3. Disposed via dispose()
+
+    After dispose(), all methods except dispose() raise EngineError.
+    """
+
+    def synthesize(self, request: SynthesisRequest) -> SynthesizedAudio:
+        """Synthesize audio from text.
+
+        Args:
+            request: The synthesis request containing text, voice, parameters, and format.
+
+        Returns:
+            SynthesizedAudio with the synthesized audio data.
+
+        Raises:
+            EngineError: On synthesis failure. Session remains usable after error.
+            EngineError: If called after dispose().
+        """
+        ...
+
+    def dispose(self) -> None:
+        """Release session resources.
+
+        This method is idempotent and safe to call multiple times.
+        It never raises exceptions (catches and logs internally).
+        After dispose(), all methods except dispose() raise EngineError.
+        """
+        ...
+
+
+@runtime_checkable
+class Engine(Protocol):
+    """Protocol for a TTS engine that creates sessions.
+
+    An Engine is a factory for EngineSession instances. It is stateless
+    and thread-safe for createSession().
+
+    Lifecycle:
+        1. Created via create_engine() (plugin contract)
+        2. Sessions created via createSession()
+        3. Disposed via dispose()
+
+    Thread Safety:
+        - createSession() is thread-safe and can be called from any thread.
+        - dispose() must be called after all sessions are disposed.
+        - Disposing engine while sessions are alive violates API contract.
+    """
+
+    def createSession(self) -> EngineSession:
+        """Create a new session for synthesis.
+
+        Returns:
+            A new EngineSession instance. Ownership transfers to caller.
+
+        Raises:
+            EngineError: On failure. No partially initialized session is returned.
+        """
+        ...
+
+    def dispose(self) -> None:
+        """Release engine resources.
+
+        Caller must ensure all sessions created by this engine are disposed
+        before calling dispose(). Disposing an engine while any session is
+        still alive violates the API contract; behavior is undefined.
+
+        This method is idempotent and safe to call multiple times.
+        It never raises exceptions (catches and logs internally).
+        After dispose(), all methods except dispose() raise EngineError.
+        """
+        ...

abogen/tts_plugin/errors.py

@@ -0,0 +1,62 @@
+"""Error hierarchy for the TTS Plugin Architecture.
+
+This module defines typed exceptions that engines raise.
+Engines should never raise raw exceptions; they must use EngineError or its subtypes.
+"""
+
+from __future__ import annotations
+
+
+class EngineError(Exception):
+    """Base exception for all engine errors.
+
+    All engine operations that can fail should raise EngineError or one of its subtypes.
+    After dispose(), all methods except dispose() raise EngineError.
+    """
+
+    pass
+
+
+class ModelNotFoundError(EngineError):
+    """Raised when a required model is not found."""
+
+    pass
+
+
+class ModelLoadError(EngineError):
+    """Raised when a model fails to load."""
+
+    pass
+
+
+class NetworkError(EngineError):
+    """Raised when a network operation fails."""
+
+    pass
+
+
+class InvalidInputError(EngineError):
+    """Raised when invalid input is provided to the engine."""
+
+    pass
+
+
+class ConfigurationError(EngineError):
+    """Raised when there is a configuration error."""
+
+    pass
+
+
+class CancelledError(EngineError):
+    """Raised when an operation is cancelled.
+
+    This is raised by synthesize() when cancel() is called during synthesis.
+    """
+
+    pass
+
+
+class InternalError(EngineError):
+    """Raised when an internal engine error occurs."""
+
+    pass

abogen/tts_plugin/host_context.py

@@ -0,0 +1,46 @@
+"""Host context for the TTS Plugin Architecture.
+
+This module defines the HostContext dataclass that provides minimal
+host services to plugins. It is the only interface through which
+plugins can access host functionality.
+"""
+
+from __future__ import annotations
+
+import logging
+from dataclasses import dataclass
+from pathlib import Path
+from typing import Protocol, runtime_checkable
+
+
+@runtime_checkable
+class HttpClient(Protocol):
+    """Protocol for HTTP client provided by host.
+
+    Plugins can use this for network requests (e.g., API-based engines).
+    """
+
+    def get(self, url: str, **kwargs: object) -> object:
+        """Perform an HTTP GET request."""
+        ...
+
+    def post(self, url: str, **kwargs: object) -> object:
+        """Perform an HTTP POST request."""
+        ...
+
+
+@dataclass(frozen=True)
+class HostContext:
+    """Minimal host context provided to plugins.
+
+    Contains only essential host services. No business logic.
+
+    Attributes:
+        config_dir: Directory for API keys, preferences, and configuration.
+        logger: Logger for plugin logging.
+        http_client: HTTP client for network requests.
+    """
+
+    config_dir: Path
+    logger: logging.Logger
+    http_client: HttpClient

abogen/tts_plugin/loader.py

@@ -0,0 +1,365 @@
+"""Plugin loader infrastructure for the TTS Plugin Architecture.
+
+This module provides functionality to discover, import, validate, and load
+TTS plugins. It handles both valid and invalid plugins, providing diagnostic
+messages for errors.
+
+The loader does NOT:
+- Create Engine instances (that's the plugin's create_engine() responsibility)
+- Manage plugin lifecycle (that's the Plugin Manager's responsibility)
+- Implement any TTS engine functionality
+"""
+
+from __future__ import annotations
+
+import importlib.util
+import re
+import sys
+import types
+from dataclasses import dataclass, field
+from pathlib import Path
+from typing import Any, Callable
+
+from abogen.tts_plugin.manifest import ModelManifest, PluginManifest
+
+
+# Host API version for compatibility checking
+HOST_API_VERSION = "1.0"
+
+
+@dataclass(frozen=True)
+class PluginLoadError:
+    """Diagnostic information for a failed plugin load.
+
+    Attributes:
+        plugin_id: Plugin identifier if available, otherwise directory name.
+        path: Path to the plugin directory.
+        errors: List of error messages describing what went wrong.
+    """
+
+    plugin_id: str
+    path: Path
+    errors: tuple[str, ...] = field(default_factory=tuple)
+
+
+@dataclass(frozen=True)
+class PluginLoadResult:
+    """Result of loading a plugin.
+
+    Attributes:
+        success: Whether the plugin loaded successfully.
+        manifest: The plugin manifest if successful.
+        model_requirements: Model requirements if successful.
+        create_engine: The create_engine function if successful.
+        module: The plugin module if successful.
+        error: Error information if failed.
+    """
+
+    success: bool
+    manifest: PluginManifest | None = None
+    model_requirements: tuple[ModelManifest, ...] | None = None
+    create_engine: Callable[..., Any] | None = None
+    module: types.ModuleType | None = None
+    error: PluginLoadError | None = None
+
+
+def _parse_api_version(version: str) -> tuple[int, int] | None:
+    """Parse an api_version string into (major, minor) tuple.
+
+    Args:
+        version: Version string in format "MAJOR.MINOR".
+
+    Returns:
+        Tuple of (major, minor) or None if invalid format.
+    """
+    match = re.match(r"^(\d+)\.(\d+)$", version)
+    if match:
+        return int(match.group(1)), int(match.group(2))
+    return None
+
+
+def _check_api_version_compatibility(plugin_version: str) -> str | None:
+    """Check if plugin api_version is compatible with host.
+
+    Architecture spec:
+    - Format: semver (MAJOR.MINOR)
+    - Compatibility: Host rejects plugin if major version differs
+    - Minor version: backward compatible, Host accepts higher minor
+
+    Args:
+        plugin_version: Plugin's api_version string.
+
+    Returns:
+        Error message if incompatible, None if compatible.
+    """
+    plugin_ver = _parse_api_version(plugin_version)
+    if plugin_ver is None:
+        return f"Invalid api_version format: '{plugin_version}'. Expected format: MAJOR.MINOR"
+
+    host_ver = _parse_api_version(HOST_API_VERSION)
+    if host_ver is None:
+        return f"Invalid host api_version format: '{HOST_API_VERSION}'"
+
+    if plugin_ver[0] != host_ver[0]:
+        return (
+            f"api_version major mismatch: plugin={plugin_ver[0]}, host={host_ver[0]}. "
+            f"Major version must match for compatibility."
+        )
+
+    return None
+
+
+def _validate_manifest(module: types.ModuleType, plugin_dir: Path) -> list[str]:
+    """Validate that a plugin module has required exports.
+
+    Args:
+        module: The imported plugin module.
+        plugin_dir: Path to the plugin directory.
+
+    Returns:
+        List of error messages (empty if valid).
+    """
+    errors: list[str] = []
+
+    # Check PLUGIN_MANIFEST
+    manifest = getattr(module, "PLUGIN_MANIFEST", None)
+    if manifest is None:
+        errors.append("Missing PLUGIN_MANIFEST export")
+    elif not isinstance(manifest, PluginManifest):
+        errors.append(
+            f"PLUGIN_MANIFEST must be a PluginManifest instance, "
+            f"got {type(manifest).__name__}"
+        )
+
+    # Check MODEL_REQUIREMENTS
+    model_reqs = getattr(module, "MODEL_REQUIREMENTS", None)
+    if model_reqs is None:
+        errors.append("Missing MODEL_REQUIREMENTS export")
+    elif not isinstance(model_reqs, list):
+        errors.append(
+            f"MODEL_REQUIREMENTS must be a list, got {type(model_reqs).__name__}"
+        )
+    else:
+        for i, req in enumerate(model_reqs):
+            if not isinstance(req, ModelManifest):
+                errors.append(
+                    f"MODEL_REQUIREMENTS[{i}] must be a ModelManifest instance, "
+                    f"got {type(req).__name__}"
+                )
+
+    # Check create_engine
+    create_engine = getattr(module, "create_engine", None)
+    if create_engine is None:
+        errors.append("Missing create_engine export")
+    elif not callable(create_engine):
+        errors.append(
+            f"create_engine must be callable, got {type(create_engine).__name__}"
+        )
+
+    return errors
+
+
+def _validate_capabilities(manifest: PluginManifest) -> list[str]:
+    """Validate plugin capabilities.
+
+    Args:
+        manifest: The plugin manifest to validate.
+
+    Returns:
+        List of error messages (empty if valid).
+    """
+    errors: list[str] = []
+
+    # Known capabilities (can be extended)
+    known_capabilities = frozenset({
+        "voice_list",
+        "preview",
+        "voice_clone",
+        "voice_blend",
+        "streaming",
+        "cancel",
+    })
+
+    for cap in manifest.capabilities:
+        if cap not in known_capabilities:
+            errors.append(f"Unknown capability: '{cap}'")
+
+    return errors
+
+
+def _validate_api_version(manifest: PluginManifest) -> list[str]:
+    """Validate api_version compatibility.
+
+    Args:
+        manifest: The plugin manifest to validate.
+
+    Returns:
+        List of error messages (empty if valid).
+    """
+    errors: list[str] = []
+    error = _check_api_version_compatibility(manifest.api_version)
+    if error:
+        errors.append(error)
+    return errors
+
+
+def load_plugin_from_dir(plugin_dir: Path) -> PluginLoadResult:
+    """Load and validate a plugin from a directory.
+
+    The plugin directory must contain an __init__.py that exports:
+    - PLUGIN_MANIFEST: PluginManifest
+    - MODEL_REQUIREMENTS: list[ModelManifest]
+    - create_engine: Callable
+
+    Args:
+        plugin_dir: Path to the plugin directory.
+
+    Returns:
+        PluginLoadResult with success status and either plugin data or error info.
+    """
+    plugin_id = plugin_dir.name
+    errors: list[str] = []
+
+    # Check if directory exists
+    if not plugin_dir.exists():
+        return PluginLoadResult(
+            success=False,
+            error=PluginLoadError(
+                plugin_id=plugin_id,
+                path=plugin_dir,
+                errors=(f"Plugin directory does not exist: {plugin_dir}",),
+            ),
+        )
+
+    # Check for __init__.py
+    init_file = plugin_dir / "__init__.py"
+    if not init_file.exists():
+        return PluginLoadResult(
+            success=False,
+            error=PluginLoadError(
+                plugin_id=plugin_id,
+                path=plugin_dir,
+                errors=("Missing __init__.py in plugin directory",),
+            ),
+        )
+
+    # Import the module
+    module_name = f"abogen.tts_plugin._loaded.{plugin_id}"
+    try:
+        # Remove from cache if already imported (for testing)
+        if module_name in sys.modules:
+            del sys.modules[module_name]
+
+        spec = importlib.util.spec_from_file_location(
+            module_name, init_file, submodule_search_locations=[]
+        )
+        if spec is None or spec.loader is None:
+            return PluginLoadResult(
+                success=False,
+                error=PluginLoadError(
+                    plugin_id=plugin_id,
+                    path=plugin_dir,
+                    errors=(f"Failed to create module spec for {init_file}",),
+                ),
+            )
+
+        module = importlib.util.module_from_spec(spec)
+        sys.modules[module_name] = module
+        spec.loader.exec_module(module)
+    except Exception as e:
+        # Clean up module from sys.modules on import failure
+        if module_name in sys.modules:
+            del sys.modules[module_name]
+        return PluginLoadResult(
+            success=False,
+            error=PluginLoadError(
+                plugin_id=plugin_id,
+                path=plugin_dir,
+                errors=(f"Failed to import plugin module: {e}",),
+            ),
+        )
+
+    # Validate manifest
+    manifest_errors = _validate_manifest(module, plugin_dir)
+    errors.extend(manifest_errors)
+
+    # If manifest is valid, perform additional validation
+    manifest = getattr(module, "PLUGIN_MANIFEST", None)
+    if isinstance(manifest, PluginManifest):
+        # Validate api_version
+        api_errors = _validate_api_version(manifest)
+        errors.extend(api_errors)
+
+        # Validate capabilities
+        cap_errors = _validate_capabilities(manifest)
+        errors.extend(cap_errors)
+
+        # Use manifest id if available
+        plugin_id = manifest.id
+
+    # Check if any errors occurred
+    if errors:
+        # Clean up module from sys.modules
+        if module_name in sys.modules:
+            del sys.modules[module_name]
+
+        return PluginLoadResult(
+            success=False,
+            error=PluginLoadError(
+                plugin_id=plugin_id,
+                path=plugin_dir,
+                errors=tuple(errors),
+            ),
+        )
+
+    # Get MODEL_REQUIREMENTS
+    model_requirements = tuple(getattr(module, "MODEL_REQUIREMENTS", []))
+    create_engine = getattr(module, "create_engine", None)
+
+    return PluginLoadResult(
+        success=True,
+        manifest=manifest,
+        model_requirements=model_requirements,
+        create_engine=create_engine,
+        module=module,
+    )
+
+
+def discover_plugins(plugin_dirs: list[Path]) -> list[PluginLoadResult]:
+    """Discover and load plugins from multiple directories.
+
+    Args:
+        plugin_dirs: List of directories to scan for plugins.
+
+    Returns:
+        List of PluginLoadResult, one per plugin directory found.
+    """
+    results: list[PluginLoadResult] = []
+
+    for plugin_dir in plugin_dirs:
+        if not plugin_dir.exists():
+            continue
+
+        # Scan for subdirectories (each is a potential plugin)
+        for item in sorted(plugin_dir.iterdir()):
+            if item.is_dir() and not item.name.startswith("."):
+                result = load_plugin_from_dir(item)
+                results.append(result)
+
+    return results
+
+
+def load_plugin(
+    plugin_dir: Path,
+) -> PluginLoadResult:
+    """Load a single plugin from a directory.
+
+    This is the main entry point for loading a plugin.
+
+    Args:
+        plugin_dir: Path to the plugin directory.
+
+    Returns:
+        PluginLoadResult with success status and either plugin data or error info.
+    """
+    return load_plugin_from_dir(plugin_dir)

abogen/tts_plugin/manifest.py

@@ -0,0 +1,189 @@
+"""Plugin manifest types for the TTS Plugin Architecture.
+
+This module contains static metadata types that describe plugins.
+These types have no dependencies and are immutable.
+"""
+
+from __future__ import annotations
+
+from dataclasses import dataclass, field
+from typing import Any
+
+
+@dataclass(frozen=True)
+class AudioFormatManifest:
+    """Manifest describing an audio format.
+
+    Attributes:
+        mime: MIME type of the audio.
+        extension: File extension.
+    """
+
+    mime: str
+    extension: str
+
+
+@dataclass(frozen=True)
+class EnumOption:
+    """Manifest describing an enum option for a parameter.
+
+    Attributes:
+        value: The enum value.
+        label: Human-readable label.
+    """
+
+    value: str
+    label: str
+
+
+@dataclass(frozen=True)
+class ParameterManifest:
+    """Manifest describing a synthesis parameter.
+
+    Attributes:
+        id: Parameter identifier.
+        name: Human-readable name.
+        description: Parameter description.
+        type: Parameter type ("float", "int", "string", "boolean", "enum").
+        default: Default value.
+        min: Minimum value (optional, for numeric types).
+        max: Maximum value (optional, for numeric types).
+        step: Step size (optional, for numeric types).
+        options: Available options (optional, for enum type).
+        unit: Unit of measurement (optional).
+        group: Parameter group (optional).
+    """
+
+    id: str
+    name: str
+    description: str
+    type: str
+    default: Any
+    min: float | None = None
+    max: float | None = None
+    step: float | None = None
+    options: tuple[EnumOption, ...] = field(default_factory=tuple)
+    unit: str | None = None
+    group: str | None = None
+
+
+@dataclass(frozen=True)
+class VoiceManifest:
+    """Manifest describing a voice.
+
+    Attributes:
+        id: Voice identifier.
+        name: Human-readable name.
+        tags: Voice tags (e.g., language, style).
+    """
+
+    id: str
+    name: str
+    tags: tuple[str, ...] = field(default_factory=tuple)
+
+
+@dataclass(frozen=True)
+class VoiceSourceManifest:
+    """Manifest describing a voice source.
+
+    Attributes:
+        id: Voice source identifier.
+        name: Human-readable name.
+        type: Source type ("list", "speaker_id", "clone", "blend", "generate", "none").
+        config: Source-specific configuration.
+    """
+
+    id: str
+    name: str
+    type: str
+    config: Any = None
+
+
+@dataclass(frozen=True)
+class EngineManifest:
+    """Manifest describing engine capabilities.
+
+    Attributes:
+        voiceSources: Available voice sources.
+        parameters: Available synthesis parameters.
+        audioFormats: Supported audio formats.
+    """
+
+    voiceSources: tuple[VoiceSourceManifest, ...] = field(default_factory=tuple)
+    parameters: tuple[ParameterManifest, ...] = field(default_factory=tuple)
+    audioFormats: tuple[AudioFormatManifest, ...] = field(default_factory=tuple)
+
+
+@dataclass(frozen=True)
+class GpuRequirement:
+    """Manifest describing GPU requirements.
+
+    Attributes:
+        required: Whether GPU is required.
+        type: GPU type (e.g., "cuda", "rocm").
+        memory: Required GPU memory in GB.
+    """
+
+    required: bool = False
+    type: str | None = None
+    memory: float | None = None
+
+
+@dataclass(frozen=True)
+class RequirementManifest:
+    """Manifest describing plugin requirements.
+
+    Attributes:
+        gpu: GPU requirements (optional).
+        memory: Required RAM in GB (optional).
+        internet: Whether internet is required (optional).
+    """
+
+    gpu: GpuRequirement | None = None
+    memory: float | None = None
+    internet: bool | None = None
+
+
+@dataclass(frozen=True)
+class ModelManifest:
+    """Manifest describing a model requirement.
+
+    Attributes:
+        id: Model identifier.
+        name: Human-readable name.
+        size: Model size as string (e.g., "100MB", "2GB").
+    """
+
+    id: str
+    name: str
+    size: str
+
+
+@dataclass(frozen=True)
+class PluginManifest:
+    """Main manifest for a TTS plugin.
+
+    Attributes:
+        id: Plugin identifier (unique).
+        name: Human-readable name.
+        version: Plugin version.
+        api_version: API version (semver format: MAJOR.MINOR).
+        description: Plugin description.
+        author: Plugin author.
+        capabilities: List of capability identifiers.
+        requires: Plugin requirements.
+        engine: Engine manifest.
+        voices: Optional static voice catalog. None = not declared (use VoiceLister),
+            empty tuple = explicitly no static voices, non-empty = static catalog.
+    """
+
+    id: str
+    name: str
+    version: str
+    api_version: str
+    description: str
+    author: str
+    capabilities: tuple[str, ...] = field(default_factory=tuple)
+    requires: RequirementManifest = field(default_factory=RequirementManifest)
+    engine: EngineManifest = field(default_factory=EngineManifest)
+    voices: tuple[VoiceManifest, ...] | None = None

abogen/tts_plugin/plugin.py

@@ -0,0 +1,55 @@
+"""Plugin contract for the TTS Plugin Architecture.
+
+This module defines the plugin contract that all TTS plugins must implement.
+Each plugin must export:
+- PLUGIN_MANIFEST: PluginManifest instance
+- MODEL_REQUIREMENTS: list of ModelManifest instances
+- create_engine(): Factory function that creates an Engine
+
+The create_engine() function is the entry point for plugin activation.
+It must be atomic: succeed fully or raise and clean up.
+"""
+
+from __future__ import annotations
+
+from pathlib import Path
+from typing import Protocol, runtime_checkable
+
+from abogen.tts_plugin.engine import Engine
+from abogen.tts_plugin.host_context import HostContext
+from abogen.tts_plugin.types import EngineConfig
+
+
+@runtime_checkable
+class Plugin(Protocol):
+    """Protocol defining the plugin contract.
+
+    Every TTS plugin must implement this protocol by exporting:
+    - PLUGIN_MANIFEST: PluginManifest
+    - MODEL_REQUIREMENTS: list[ModelManifest]
+    - create_engine: Callable[[HostContext, Path | None, EngineConfig], Engine]
+    """
+
+    def create_engine(
+        self,
+        context: HostContext,
+        model_path: Path | None,
+        config: EngineConfig,
+    ) -> Engine:
+        """Create an engine instance.
+
+        This is the factory function that creates an Engine from a plugin.
+        It must be atomic: succeed fully or raise EngineError and clean up.
+
+        Args:
+            context: Host services (config dir, logger, http client).
+            model_path: Resolved model path, or None for cloud/no-model engines.
+            config: Engine initialization settings.
+
+        Returns:
+            A fully initialized Engine instance.
+
+        Raises:
+            EngineError: On failure. Cleans up partially created resources.
+        """
+        ...

abogen/tts_plugin/plugin_manager.py

@@ -0,0 +1,156 @@
+"""Plugin Manager
+
+Provides a simple interface for consumers to access TTS engines via the
+new Plugin Architecture. Discovers, loads, and manages plugins from the
+plugins directory.
+
+Usage:
+    from abogen.tts_plugin.plugin_manager import get_plugin_manager
+
+    manager = get_plugin_manager()
+    engine = manager.create_engine("kokoro", language=Language.EN_US, device="cpu")
+    session = engine.create_session()
+    try:
+        result = session.synthesize("Hello world")
+    finally:
+        session.dispose()
+"""
+
+from typing import Any, Dict, List, Optional, Type
+
+from abogen.tts_plugin.engine import Engine, EngineSession
+from abogen.tts_plugin.manifest import PluginManifest
+from abogen.tts_plugin.types import AudioFormat
+
+
+class PluginManager:
+    """Manages TTS plugins and provides a simple interface for consumers."""
+
+    def __init__(self) -> None:
+        self._plugins: Dict[str, dict] = {}
+        self._engines: Dict[str, Engine] = {}
+        self._loaded = False
+
+    def discover(self, plugins_dir: str = "plugins") -> None:
+        """Discover and load all plugins from the given directory."""
+        import os
+        from pathlib import Path
+        from abogen.tts_plugin.loader import load_plugin_from_dir
+
+        self._plugins.clear()
+        self._engines.clear()
+
+        plugins_path = Path(plugins_dir)
+        if not plugins_path.exists():
+            if plugins_dir == "plugins":
+                plugins_path = Path(__file__).resolve().parent.parent.parent / "plugins"
+            if not plugins_path.exists():
+                self._loaded = True
+                return
+
+        for entry in plugins_path.iterdir():
+            if entry.is_dir() and (entry / "__init__.py").exists():
+                try:
+                    result = load_plugin_from_dir(entry)
+                    if result.success and result.manifest is not None:
+                        self._plugins[result.manifest.id] = {
+                            "manifest": result.manifest,
+                            "create_engine": result.create_engine,
+                            "module": result.module,
+                        }
+                except Exception as e:
+                    # Log error but continue with other plugins
+                    print(f"Warning: Failed to load plugin from {entry}: {e}")
+
+        self._loaded = True
+
+    def _ensure_loaded(self) -> None:
+        """Ensure plugins have been discovered."""
+        if not self._loaded:
+            self.discover()
+
+    def list_plugins(self) -> List[PluginManifest]:
+        """Return manifests for all loaded plugins."""
+        self._ensure_loaded()
+        return [info["manifest"] for info in self._plugins.values()]
+
+    def get_plugin(self, plugin_id: str) -> Optional[dict]:
+        """Get plugin info by ID."""
+        self._ensure_loaded()
+        return self._plugins.get(plugin_id)
+
+    def has_plugin(self, plugin_id: str) -> bool:
+        """Check if a plugin is loaded."""
+        self._ensure_loaded()
+        return plugin_id in self._plugins
+
+    def create_engine(self, plugin_id: str, **kwargs: Any) -> Engine:
+        """Create an engine instance for the given plugin.
+
+        Args:
+            plugin_id: The plugin identifier (e.g., "kokoro")
+            **kwargs: Arguments passed to the engine constructor
+
+        Returns:
+            An Engine instance
+
+        Raises:
+            KeyError: If plugin_id is not found
+            Exception: If engine creation fails
+        """
+        self._ensure_loaded()
+
+        if plugin_id not in self._plugins:
+            raise KeyError(f"Plugin not found: {plugin_id}")
+
+        plugin_info = self._plugins[plugin_id]
+        create_engine_func = plugin_info["create_engine"]
+
+        # Create engine using the plugin's factory
+        engine = create_engine_func(**kwargs)
+        return engine
+
+    def get_or_create_engine(self, plugin_id: str, **kwargs: Any) -> Engine:
+        """Get an existing engine or create a new one.
+
+        Engines are cached by plugin_id. If you need multiple instances
+        with different parameters, use create_engine() directly.
+        """
+        self._ensure_loaded()
+
+        cache_key = plugin_id
+        if cache_key in self._engines:
+            return self._engines[cache_key]
+
+        engine = self.create_engine(plugin_id, **kwargs)
+        self._engines[cache_key] = engine
+        return engine
+
+    def dispose_all(self) -> None:
+        """Dispose all cached engines."""
+        for engine in self._engines.values():
+            try:
+                engine.dispose()
+            except Exception:
+                pass  # dispose() should never raise
+        self._engines.clear()
+
+
+# Global singleton
+_manager: Optional[PluginManager] = None
+
+
+def get_plugin_manager() -> PluginManager:
+    """Get the global PluginManager instance."""
+    global _manager
+    if _manager is None:
+        _manager = PluginManager()
+    return _manager
+
+
+def reset_plugin_manager() -> None:
+    """Reset the global PluginManager (for testing)."""
+    global _manager
+    if _manager is not None:
+        _manager.dispose_all()
+    _manager = None

abogen/tts_plugin/types.py

@@ -0,0 +1,113 @@
+"""Core domain types for the TTS Plugin Architecture.
+
+This module contains immutable value objects that form the core domain.
+These types have zero dependencies and are used across the plugin system.
+"""
+
+from __future__ import annotations
+
+from dataclasses import dataclass, field
+from typing import Any, Mapping
+
+from abogen.domain.enums import Language
+
+
+@dataclass(frozen=True)
+class AudioFormat:
+    """Immutable value object representing an audio format.
+
+    Attributes:
+        mime: MIME type of the audio (e.g., "audio/wav", "audio/mpeg").
+        extension: File extension (e.g., "wav", "mp3").
+    """
+
+    mime: str
+    extension: str
+
+
+@dataclass(frozen=True)
+class Duration:
+    """Immutable value object representing a time duration.
+
+    Attributes:
+        seconds: Duration in seconds.
+    """
+
+    seconds: float
+
+
+@dataclass(frozen=True)
+class VoiceSelection:
+    """Immutable value object for voice selection. Opaque to engine.
+
+    Attributes:
+        source: Voice source identifier (e.g., "builtin", "clone").
+        key: Voice key within the source.
+        payload: Optional payload for clone/blend sources.
+    """
+
+    source: str
+    key: str
+    payload: Any = None
+
+
+@dataclass(frozen=True)
+class ParameterValues:
+    """Immutable value object for synthesis parameters. Behaves like Mapping[str, Any].
+
+    Attributes:
+        values: Mapping of parameter names to their values.
+    """
+
+    values: Mapping[str, Any] = field(default_factory=dict)
+
+
+@dataclass(frozen=True)
+class SynthesisRequest:
+    """Immutable value object for a synthesis request.
+
+    Attributes:
+        text: Text to synthesize.
+        voice: Voice selection.
+        parameters: Synthesis parameters.
+        format: Desired audio output format.
+    """
+
+    text: str
+    voice: VoiceSelection
+    parameters: ParameterValues
+    format: AudioFormat
+
+
+@dataclass(frozen=True)
+class SynthesizedAudio:
+    """Immutable value object for synthesized audio result.
+
+    Attributes:
+        data: Raw audio bytes.
+        format: Audio format of the result.
+        duration: Duration of the audio.
+    """
+
+    data: bytes
+    format: AudioFormat
+    duration: Duration
+
+
+@dataclass(frozen=True)
+class EngineConfig:
+    """Immutable configuration of an Engine instance.
+
+    Contains parameters that define how a particular Engine instance is
+    created and that remain constant throughout the lifetime of that Engine.
+
+    Plugin implementations may ignore fields that are not applicable to them.
+
+    Attributes:
+        device: Device to use (e.g., "cpu", "cuda:0").
+        language: Language enum value. The engine converts to its internal
+            format internally — callers never see engine-specific codes.
+    """
+
+    device: str = "cpu"
+    language: Language = Language.EN_US

abogen/tts_plugin/utils.py

@@ -0,0 +1,242 @@
+"""TTS Plugin Architecture — direct utility functions.
+
+Provides helpers that replace the former compatibility adapter by
+calling the Plugin Manager directly.
+"""
+
+from __future__ import annotations
+
+from typing import Any, Iterator
+
+import numpy as np
+
+from abogen.domain.enums import Language
+from abogen.tts_plugin.plugin_manager import get_plugin_manager
+
+
+def get_voices(plugin_id: str) -> tuple[str, ...]:
+    """Return the voice-id tuple for *plugin_id*.
+
+    Uses the official Plugin Architecture: PluginManager → Engine → VoiceLister.
+    First checks plugin manifest for static voice catalog.
+    """
+    import logging
+    import tempfile
+    from pathlib import Path
+
+    from abogen.tts_plugin.host_context import HostContext
+    from abogen.tts_plugin.types import EngineConfig
+
+    manager = get_plugin_manager()
+    if not manager.has_plugin(plugin_id):
+        return ()
+
+    # Check manifest for static voice catalog
+    plugin_info = manager.get_plugin(plugin_id)
+    if plugin_info is not None:
+        manifest = plugin_info.get("manifest")
+        if manifest is not None and manifest.voices is not None:
+            return tuple(v.id for v in manifest.voices)
+
+    ctx = HostContext(
+        config_dir=Path(tempfile.gettempdir()),
+        logger=logging.getLogger(f"abogen.utils.{plugin_id}"),
+        http_client=type("_StubHttpClient", (), {
+            "get": staticmethod(lambda url, **kw: None),
+            "post": staticmethod(lambda url, **kw: None),
+        })(),
+    )
+
+    try:
+        engine = manager.create_engine(
+            plugin_id,
+            context=ctx,
+            model_path=None,
+            config=EngineConfig(device="cpu"),
+        )
+    except Exception:
+        return ()
+
+    try:
+        from abogen.tts_plugin.capabilities import VoiceLister
+
+        if isinstance(engine, VoiceLister):
+            manifests = engine.listVoices("builtin")
+            return tuple(v.id for v in manifests)
+        return ()
+    except Exception:
+        return ()
+    finally:
+        engine.dispose()
+
+
+def get_default_voice(plugin_id: str, fallback: str = "") -> str:
+    """Return the first voice of *plugin_id*, or *fallback*."""
+    voices = get_voices(plugin_id)
+    return voices[0] if voices else fallback
+
+
+def is_plugin_registered(plugin_id: str) -> bool:
+    """Check whether *plugin_id* is loaded by the Plugin Manager."""
+    return get_plugin_manager().has_plugin(plugin_id)
+
+
+def resolve_voice_to_plugin(spec: str, fallback: str = "kokoro") -> str:
+    """Determine which plugin owns the given voice specification.
+
+    Resolution rules:
+    1. Empty spec -> fallback
+    2. Kokoro formula (contains '*' or '+') -> "kokoro"
+    3. Exact voice-id match against loaded plugins -> plugin id
+    4. Unknown voice -> fallback
+    """
+    raw = str(spec or "").strip()
+    if not raw:
+        return fallback
+
+    if "*" in raw or "+" in raw:
+        return "kokoro"
+
+    upper = raw.upper()
+    manager = get_plugin_manager()
+
+    for manifest in manager.list_plugins():
+        for voice_source in manifest.engine.voiceSources:
+            if voice_source.type == "list" and isinstance(voice_source.config, dict):
+                try:
+                    engine = manager.create_engine(manifest.id)
+                    try:
+                        if hasattr(engine, "listVoices"):
+                            voice_manifests = engine.listVoices(voice_source.id)
+                            voice_ids = [v.id.upper() for v in voice_manifests]
+                            if upper in voice_ids:
+                                return manifest.id
+                    finally:
+                        engine.dispose()
+                except Exception:
+                    continue
+
+    return fallback
+
+
+class Pipeline:
+    """Callable wrapper around Engine / EngineSession.
+
+    Presents the same interface that old callers expect::
+
+        pipeline = create_pipeline("kokoro", language=Language.EN_US, device="cpu")
+        for segment in pipeline(text, voice="af_nova", speed=1.0):
+            audio = segment.audio
+    """
+
+    def __init__(self, engine: Any, **engine_kwargs: Any) -> None:
+        self._engine = engine
+        self._engine_kwargs = engine_kwargs
+        self._session: Any = None
+
+    def _ensure_session(self) -> Any:
+        if self._session is None:
+            self._session = self._engine.createSession()
+        return self._session
+
+    def __call__(
+        self,
+        text: str,
+        voice: str = "default",
+        speed: float = 1.0,
+        split_pattern: str | None = None,
+        **kwargs: Any,
+    ) -> Iterator[Any]:
+        from abogen.tts_plugin.types import (
+            AudioFormat,
+            ParameterValues,
+            SynthesisRequest,
+            VoiceSelection,
+        )
+
+        session = self._ensure_session()
+
+        params: dict[str, Any] = {"speed": speed}
+        if split_pattern is not None:
+            params["split_pattern"] = split_pattern
+        params.update(kwargs)
+
+        request = SynthesisRequest(
+            text=text,
+            voice=VoiceSelection(source="builtin", key=voice),
+            parameters=ParameterValues(values=params),
+            format=AudioFormat(mime="audio/wav", extension="wav"),
+        )
+
+        result = session.synthesize(request)
+        audio_array = np.frombuffer(result.data, dtype=np.float32)
+
+        from dataclasses import dataclass
+
+        @dataclass
+        class Segment:
+            graphemes: str
+            audio: np.ndarray
+
+        yield Segment(graphemes=text, audio=audio_array)
+
+    def load_single_voice(self, voice_name: str) -> Any:
+        engine_pipeline = getattr(self._engine, '_pipeline', None)
+        if engine_pipeline is not None and hasattr(engine_pipeline, 'load_single_voice'):
+            return engine_pipeline.load_single_voice(voice_name)
+        raise AttributeError(f"load_single_voice not available on {type(self._engine).__name__}")
+
+    def dispose(self) -> None:
+        if self._session is not None:
+            try:
+                self._session.dispose()
+            except Exception:
+                pass
+            self._session = None
+
+    def __del__(self) -> None:
+        self.dispose()
+
+
+def create_pipeline(
+    plugin_id: str,
+    *,
+    language: Language = Language.EN_US,
+    device: str = "cpu",
+) -> Pipeline:
+    """Create a callable TTS pipeline via the Plugin Architecture.
+
+    Builds a proper HostContext and EngineConfig, then delegates to the
+    PluginManager to create the engine. Returns a :class:`Pipeline` whose
+    ``__call__`` interface matches the callable protocol used by consumers.
+
+    Args:
+        plugin_id: Plugin identifier (e.g., "kokoro", "supertonic").
+        language: Language enum value (app-layer type, not engine-specific).
+        device: Device to use (e.g., "cpu", "cuda:0").
+
+    Returns:
+        A callable Pipeline instance.
+    """
+    import logging
+    import tempfile
+    from pathlib import Path
+
+    from abogen.tts_plugin.host_context import HostContext
+    from abogen.tts_plugin.types import EngineConfig
+
+    manager = get_plugin_manager()
+
+    ctx = HostContext(
+        config_dir=Path(tempfile.gettempdir()),
+        logger=logging.getLogger(f"abogen.pipeline.{plugin_id}"),
+        http_client=type("_StubHttpClient", (), {
+            "get": staticmethod(lambda url, **kw: None),
+            "post": staticmethod(lambda url, **kw: None),
+        })(),
+    )
+
+    config = EngineConfig(device=device, language=language)
+
+    engine = manager.create_engine(plugin_id, context=ctx, model_path=None, config=config)
+    return Pipeline(engine)

abogen/utils.py

@@ -428,19 +428,6 @@ def save_config(config):
         pass
 
 
-def calculate_text_length(text):
-    # Ignore chapter markers
-    text = re.sub(r"<<CHAPTER_MARKER:.*?>>", "", text)
-    # Ignore metadata patterns
-    text = re.sub(r"<<METADATA_[^:]+:[^>]*>>", "", text)
-    # Ignore newlines
-    text = text.replace("\n", "")
-    # Ignore leading/trailing spaces
-    text = text.strip()
-    # Calculate character count
-    char_count = len(text)
-    return char_count
-
 
 def get_gpu_acceleration(enabled):
     try:
@@ -529,21 +516,20 @@ def prevent_sleep_end():
                 _sleep_procs[system] = None
 
 
-def load_numpy_kpipeline():
-    import numpy as np
-    from kokoro import KPipeline  # type: ignore[import-not-found]
-
-    return np, KPipeline
-
-
 class LoadPipelineThread(Thread):
-    def __init__(self, callback):
+    def __init__(self, callback, lang_code="a", use_gpu=True):
         super().__init__()
         self.callback = callback
+        self.lang_code = lang_code
+        self.use_gpu = use_gpu
 
     def run(self):
         try:
-            np_module, kpipeline_class = load_numpy_kpipeline()
-            self.callback(np_module, kpipeline_class, None)
+            from abogen.domain.pipeline_factory import create_pipeline_for_job
+
+            backend = create_pipeline_for_job(
+                "kokoro", language=self.lang_code, use_gpu=self.use_gpu
+            )
+            self.callback(backend, None)
         except Exception as e:
-            self.callback(None, None, str(e))
+            self.callback(None, str(e))

abogen/voice_cache.py

@@ -17,7 +17,7 @@ if LocalEntryNotFoundError is None:  # pragma: no cover - fallback for tests
         pass
 
 
-from abogen.constants import VOICES_INTERNAL
+from abogen.tts_plugin.utils import get_voices
 
 _CACHE_LOCK = threading.Lock()
 _CACHED_VOICES: Set[str] = set()
@@ -26,8 +26,9 @@ _BOOTSTRAPPED = False
 
 
 def _normalize_targets(voices: Optional[Iterable[str]]) -> Set[str]:
+    kokoro_voices = get_voices("kokoro")
     if not voices:
-        return set(VOICES_INTERNAL)
+        return set(kokoro_voices)
     normalized: Set[str] = set()
     for voice in voices:
         if not voice:
@@ -35,7 +36,7 @@ def _normalize_targets(voices: Optional[Iterable[str]]) -> Set[str]:
         voice_id = str(voice).strip()
         if not voice_id:
             continue
-        if voice_id in VOICES_INTERNAL:
+        if voice_id in kokoro_voices:
             normalized.add(voice_id)
     return normalized
 
@@ -143,3 +144,11 @@ def _ensure_single_voice_asset(
 
     hf_hub_download(resume_download=True, **common_kwargs)
     return True
+
+
+def clear_voice_cache() -> None:
+    """Clear the in‑process voice cache (used during shutdown)."""
+    with _CACHE_LOCK:
+        _CACHED_VOICES.clear()
+    global _BOOTSTRAPPED
+    _BOOTSTRAPPED = False

abogen/voice_formulas.py

@@ -1,7 +1,7 @@
 import re
-from typing import List, Tuple
+from typing import Iterable, List, Optional, Tuple
 
-from abogen.constants import VOICES_INTERNAL
+from abogen.tts_plugin.utils import get_voices
 
 
 # Calls parsing and loads the voice to gpu or cpu
@@ -22,6 +22,7 @@ def parse_formula_terms(formula: str) -> List[Tuple[str, float]]:
         raise ValueError("Empty voice formula")
 
     terms: List[Tuple[str, float]] = []
+    kokoro_voices = get_voices("kokoro")
     for segment in formula.split("+"):
         part = segment.strip()
         if not part:
@@ -30,7 +31,7 @@ def parse_formula_terms(formula: str) -> List[Tuple[str, float]]:
             raise ValueError("Each component must be in the form voice*weight")
         voice_name, raw_weight = part.split("*", 1)
         voice_name = voice_name.strip()
-        if voice_name not in VOICES_INTERNAL:
+        if voice_name not in kokoro_voices:
             raise ValueError(f"Unknown voice: {voice_name}")
         try:
             weight = float(raw_weight.strip())
@@ -71,6 +72,33 @@ def parse_voice_formula(pipeline, formula):
     return weighted_sum
 
 
+def pairs_to_formula(pairs: Iterable[Tuple[str, float]]) -> Optional[str]:
+    """Build a voice formula string from (voice_name, weight) pairs.
+
+    Normalizes weights to sum to 1.0 and formats as "voice1*0.5+voice2*0.5".
+
+    Args:
+        pairs: Iterable of (voice_name, weight) tuples. Zero-weight entries
+            are filtered out.
+
+    Returns:
+        Formula string, or None if no valid entries.
+    """
+    voices = [(voice, float(weight)) for voice, weight in pairs if weight is not None and float(weight) > 0]
+    if not voices:
+        return None
+    total = sum(weight for _, weight in voices)
+    if total <= 0:
+        return None
+
+    def _format_value(value: float) -> str:
+        normalized = value / total if total else 0.0
+        return (f"{normalized:.4f}").rstrip("0").rstrip(".") or "0"
+
+    parts = [f"{voice}*{_format_value(weight)}" for voice, weight in voices]
+    return "+".join(parts)
+
+
 def calculate_sum_from_formula(formula):
     weights = re.findall(r"\* *([\d.]+)", formula)
     total_sum = sum(float(weight) for weight in weights)

abogen/voice_metadata.py

@@ -0,0 +1,33 @@
+from dataclasses import dataclass
+
+
+@dataclass(frozen=True)
+class VoiceMetadata:
+    """
+    Immutable metadata describing a voice from a TTS backend.
+
+    This model describes a voice independently of any backend implementation.
+    Backends populate these objects; the application consumes them.
+
+    The ``backend_id`` field is set by the backend itself (via
+    ``self.metadata.id``) — the application never hardcodes it.
+    This ensures renaming a backend does not require touching voice definitions.
+    """
+
+    id: str
+    """Unique voice identifier within the backend (e.g. ``"af_alloy"``, ``"M1"``)."""
+
+    display_name: str
+    """Human-readable display name (e.g. ``"Alloy"``, ``"Male 1"``)."""
+
+    language: str
+    """Language code — backend-specific format is acceptable (e.g. ``"a"``, ``"en"``)."""
+
+    gender: str
+    """Gender category: ``"female"``, ``"male"``, or ``"unknown"``."""
+
+    backend_id: str
+    """Identifier of the backend that owns this voice (e.g. ``"kokoro"``).
+
+    Set automatically by the backend — never hardcoded in voice definitions.
+    """

abogen/voice_profiles.py

@@ -2,8 +2,7 @@ import json
 import os
 from typing import Any, Dict, Iterable, List, Tuple
 
-from abogen.constants import VOICES_INTERNAL
-from abogen.tts_supertonic import DEFAULT_SUPERTONIC_VOICES
+from abogen.tts_plugin.utils import get_voices, is_plugin_registered
 from abogen.utils import get_user_config_path
 
 
@@ -70,7 +69,8 @@ def serialize_profiles() -> Dict[str, Dict[str, Iterable[Tuple[str, float]]]]:
 
 def _normalize_supertonic_voice(value: Any) -> str:
     raw = str(value or "").strip().upper()
-    return raw if raw in DEFAULT_SUPERTONIC_VOICES else "M1"
+    supertonic_voices = get_voices("supertonic")
+    return raw if raw in supertonic_voices else "M1"
 
 
 def _coerce_supertonic_steps(value: Any) -> int:
@@ -101,7 +101,7 @@ def normalize_profile_entry(entry: Any) -> Dict[str, Any]:
         return {}
 
     provider = str(entry.get("provider") or "kokoro").strip().lower()
-    if provider not in {"kokoro", "supertonic"}:
+    if not is_plugin_registered(provider):
         provider = "kokoro"
 
     language = str(entry.get("language") or "a").strip().lower() or "a"
@@ -135,6 +135,7 @@ def normalize_profile_entry(entry: Any) -> Dict[str, Any]:
 
 def _normalize_voice_entries(entries: Iterable) -> List[Tuple[str, float]]:
     normalized: List[Tuple[str, float]] = []
+    kokoro_voices = get_voices("kokoro")
     for item in entries or []:
         if isinstance(item, dict):
             voice = item.get("id") or item.get("voice")
@@ -143,7 +144,7 @@ def _normalize_voice_entries(entries: Iterable) -> List[Tuple[str, float]]:
             voice, weight = item[0], item[1]
         else:
             continue
-        if voice not in VOICES_INTERNAL:
+        if voice not in kokoro_voices:
             continue
         if weight is None:
             continue

abogen/webui/Dockerfile

@@ -2,7 +2,6 @@ FROM nvidia/cuda:12.6.3-cudnn-runtime-ubuntu22.04
 
 ENV PYTHONDONTWRITEBYTECODE=1 \
   PYTHONUNBUFFERED=1 \
-  PIP_NO_CACHE_DIR=1 \
   VIRTUAL_ENV=/opt/venv \
   PATH=/opt/venv/bin:$PATH
 
@@ -27,22 +26,22 @@ RUN python3 -m venv "$VIRTUAL_ENV"
 WORKDIR /app
 
 COPY pyproject.toml README.md ./
-COPY abogen ./abogen
-
-RUN pip install --upgrade pip \
+RUN pip install uv \
   && if [ -n "$TORCH_VERSION" ]; then \
-       pip install torch=="$TORCH_VERSION" torchvision=="$TORCH_VERSION" torchaudio=="$TORCH_VERSION" --index-url "$TORCH_INDEX_URL"; \
+       uv pip install --system torch=="$TORCH_VERSION" torchvision=="$TORCH_VERSION" torchaudio=="$TORCH_VERSION" --index-url "$TORCH_INDEX_URL"; \
      else \
-       pip install torch torchvision torchaudio --index-url "$TORCH_INDEX_URL"; \
+       uv pip install --system torch torchvision torchaudio --index-url "$TORCH_INDEX_URL"; \
      fi \
-  && pip install --no-cache-dir . \
+  && uv pip install --system . \
     https://github.com/explosion/spacy-models/releases/download/en_core_web_sm-3.8.0/en_core_web_sm-3.8.0-py3-none-any.whl \
-  && pip install --no-cache-dir "mutagen>=1.47.0"
+  && uv pip install --system "mutagen>=1.47.0"
+
+COPY abogen ./abogen
 
 # Install onnxruntime-gpu for CUDA acceleration (supertonic uses ONNX Runtime)
 # Set USE_GPU=false to skip this for CPU-only deployments
 RUN if [ "$USE_GPU" = "true" ]; then \
-      pip install --no-cache-dir onnxruntime-gpu; \
+      uv pip install --system onnxruntime-gpu; \
     fi
 
 ENV ABOGEN_HOST=0.0.0.0 \

abogen/webui/app.py

@@ -1,6 +1,5 @@
 from __future__ import annotations
 
-import atexit
 import logging
 import os
 from pathlib import Path
@@ -8,6 +7,8 @@ from typing import Any, Optional
 
 from flask import Flask
 
+from abogen import shutdown  # noqa: F401
+shutdown.register_shutdown()
 from abogen.utils import get_user_cache_path, get_user_output_path, get_user_settings_dir
 
 from .conversion_runner import run_conversion_job
@@ -28,6 +29,13 @@ class _SuppressSuccessfulAccessFilter(logging.Filter):
         return " 200 " not in message and " 201 " not in message and " 204 " not in message
 
 
+class _SuppressPhonemizerWarnings(logging.Filter):
+    """Suppress phonemizer word-count-mismatch warnings (normal behavior)."""
+
+    def filter(self, record: logging.LogRecord) -> bool:  # pragma: no cover - small utility
+        return "words count mismatch" not in record.getMessage()
+
+
 _access_log_filter_attached = False
 
 
@@ -83,6 +91,12 @@ def create_app(config: Optional[dict[str, Any]] = None) -> Flask:
         "UPLOAD_FOLDER": str(uploads_dir),
         "OUTPUT_FOLDER": str(outputs_dir),
         "MAX_CONTENT_LENGTH": 1024 * 1024 * 400,  # 400 MB uploads
+        # Large books can submit four form fields per chapter. Werkzeug's
+        # defaults reject those requests before the wizard route can process
+        # them, even though the encoded payload is much smaller than the upload
+        # limit above.
+        "MAX_FORM_MEMORY_SIZE": 10 * 1024 * 1024,
+        "MAX_FORM_PARTS": 10_000,
     }
     if config:
         base_config.update(config)
@@ -113,11 +127,10 @@ def create_app(config: Optional[dict[str, Any]] = None) -> Flask:
     app.register_blueprint(books_bp, url_prefix="/find-books")
     app.register_blueprint(api_bp, url_prefix="/api")
 
-    atexit.register(service.shutdown)
-
     global _access_log_filter_attached
     if not _access_log_filter_attached:
         logging.getLogger("werkzeug").addFilter(_SuppressSuccessfulAccessFilter())
+        logging.getLogger("phonemizer").addFilter(_SuppressPhonemizerWarnings())
         _access_log_filter_attached = True
 
     return app

abogen/webui/debug_tts_runner.py

@@ -14,8 +14,13 @@ from abogen.kokoro_text_normalization import normalize_for_pipeline
 from abogen.normalization_settings import build_apostrophe_config
 from abogen.text_extractor import extract_from_path
 from abogen.voice_cache import ensure_voice_assets
-from abogen.webui.conversion_runner import SAMPLE_RATE, SPLIT_PATTERN, _select_device, _to_float32, _resolve_voice, _spec_to_voice_ids
-from abogen.utils import load_numpy_kpipeline
+from abogen.domain.device import select_device as _select_device
+from abogen.domain.audio_helpers import to_float32 as _to_float32, SAMPLE_RATE
+from abogen.domain.voice_resolution import spec_to_voice_ids as _spec_to_voice_ids
+from abogen.domain.voice_loader import resolve_voice
+from abogen.domain.split_pattern import get_split_pattern
+from abogen.domain.enums import Language
+from abogen.tts_plugin.utils import create_pipeline
 
 
 _MARKER_RE = re.compile(re.escape(MARKER_PREFIX) + r"(?P<code>[A-Z0-9_]+)" + re.escape(MARKER_SUFFIX))
@@ -41,12 +46,11 @@ def _resolve_voice_setting(value: str) -> tuple[str, Optional[str], Optional[str
     return resolve_voice_setting(value)
 
 
-def _load_pipeline(language: str, use_gpu: bool) -> Any:
+def _load_pipeline(language: Language, use_gpu: bool) -> Any:
     device = "cpu"
     if use_gpu:
         device = _select_device()
-    _np, KPipeline = load_numpy_kpipeline()
-    return KPipeline(lang_code=language, repo_id="hexgrad/Kokoro-82M", device=device)
+    return create_pipeline("kokoro", language=language, device=device)
 
 
 def _extract_cases_from_text(text: str) -> List[Tuple[str, str]]:
@@ -126,32 +130,14 @@ def run_debug_tts_wavs(
     if missing:
         raise RuntimeError(f"Debug EPUB missing expected codes: {', '.join(missing)}")
 
-    language = str(settings.get("language") or "a").strip() or "a"
-    # Kokoro's KPipeline expects short language codes like "a" (American English),
-    # but older settings may store ISO-like values such as "en".
-    language_aliases = {
-        "en": "a",
-        "en-us": "a",
-        "en_us": "a",
-        "en-gb": "b",
-        "en_gb": "b",
-        "es": "e",
-        "es-es": "e",
-        "fr": "f",
-        "fr-fr": "f",
-        "hi": "h",
-        "it": "i",
-        "pt": "p",
-        "pt-br": "p",
-        "ja": "j",
-        "jp": "j",
-        "zh": "z",
-        "zh-cn": "z",
-    }
-    language = language_aliases.get(language.lower(), language)
+    raw_language = str(settings.get("language") or "en-US").strip() or "en-US"
+    try:
+        language = Language.from_str(raw_language)
+    except ValueError:
+        language = Language.EN_US
     voice_spec = str(settings.get("default_voice") or "").strip()
     use_gpu = bool(settings.get("use_gpu", False))
-    speed = float(settings.get("default_speed", 1.0) or 1.0)
+    speed = float(settings.get("default_speed") or 1.0)
 
     # Settings may store "profile:<name>" which is not a Kokoro voice ID.
     # Resolve it to a concrete voice formula (e.g. "af_heart*0.5+...") so Kokoro
@@ -161,7 +147,10 @@ def run_debug_tts_wavs(
         if resolved_voice:
             voice_spec = resolved_voice
         if profile_language:
-            language = str(profile_language).strip() or language
+            try:
+                language = Language.from_str(str(profile_language).strip()) or language
+            except (ValueError, AttributeError):
+                pass
     except Exception:
         # Voice profile resolution is best-effort; fall back to raw voice_spec.
         pass
@@ -176,7 +165,7 @@ def run_debug_tts_wavs(
             pass
 
     pipeline = _load_pipeline(language, use_gpu)
-    voice_choice = _resolve_voice(pipeline, voice_spec, use_gpu)
+    voice_choice = resolve_voice(voice_spec, pipeline, use_gpu)
 
     apostrophe_config = build_apostrophe_config(settings=settings)
     normalization_settings = dict(settings)
@@ -201,7 +190,7 @@ def run_debug_tts_wavs(
             normalized,
             voice=voice_choice,
             speed=speed,
-            split_pattern=SPLIT_PATTERN,
+            split_pattern=get_split_pattern(language, "Disabled"),
         ):
             audio = _to_float32(getattr(segment, "audio", None))
             if audio.size:
@@ -248,4 +237,8 @@ def run_debug_tts_wavs(
         "sample_rate": SAMPLE_RATE,
     }
     (run_dir / "manifest.json").write_text(json.dumps(manifest, indent=2), encoding="utf-8")
+    try:
+        pipeline.dispose()
+    except Exception:
+        pass
     return manifest

abogen/webui/routes/api.py

@@ -6,6 +6,7 @@ from pathlib import Path
 from flask import Blueprint, request, jsonify, send_file, url_for, current_app
 from flask.typing import ResponseReturnValue
 
+from abogen.domain.enums import Language
 from abogen.webui.routes.utils.settings import (
     load_settings,
     load_integration_settings,
@@ -25,7 +26,7 @@ from abogen.voice_profiles import (
     normalize_profile_entry,
 )
 from abogen.webui.routes.utils.common import split_profile_spec
-from abogen.webui.routes.utils.preview import synthesize_preview, generate_preview_audio
+from abogen.webui.routes.utils.synthesize import synthesize_preview, generate_preview_audio
 from abogen.webui.routes.utils.voice import formula_from_profile
 from abogen.normalization_settings import (
     build_llm_configuration,
@@ -34,6 +35,7 @@ from abogen.normalization_settings import (
 )
 from abogen.llm_client import list_models, LLMClientError
 from abogen.kokoro_text_normalization import normalize_for_pipeline
+from abogen.tts_plugin.utils import is_plugin_registered
 from abogen.integrations.audiobookshelf import AudiobookshelfClient, AudiobookshelfConfig
 from abogen.integrations.calibre_opds import (
     CalibreOPDSClient,
@@ -46,6 +48,21 @@ from werkzeug.utils import secure_filename
 
 api_bp = Blueprint("api", __name__)
 
+
+def _parse_language(value: Any) -> Language:
+    """Parse a frontend language value to Language enum.
+
+    This is the API boundary — frontend sends strings, backend parses
+    to Language enum. No engine-specific codes leak outside the engine.
+    """
+    if isinstance(value, Language):
+        return value
+    try:
+        return Language.from_str(str(value or "").strip())
+    except (ValueError, AttributeError):
+        return Language.EN_US
+
+
 # --- Voice Profile Routes ---
 
 @api_bp.get("/voice-profiles")
@@ -63,7 +80,7 @@ def api_save_voice_profile() -> ResponseReturnValue:
     if profile is None:
         # Speaker Studio payload format
         provider = str(payload.get("provider") or "kokoro").strip().lower()
-        if provider not in {"kokoro", "supertonic"}:
+        if not is_plugin_registered(provider):
             provider = "kokoro"
         if provider == "supertonic":
             profile = {
@@ -151,7 +168,7 @@ def api_export_voice_profiles() -> ResponseReturnValue:
 def api_voice_profiles_preview() -> ResponseReturnValue:
     payload = request.get_json(force=True, silent=True) or {}
     text = str(payload.get("text") or "").strip() or "Hello world"
-    language = str(payload.get("language") or "a").strip().lower() or "a"
+    language = _parse_language(payload.get("language"))
     speed = coerce_float(payload.get("speed"), 1.0)
     max_seconds = coerce_float(payload.get("max_seconds"), 8.0)
 
@@ -167,6 +184,11 @@ def api_voice_profiles_preview() -> ResponseReturnValue:
     voice_spec = ""
     resolved_provider = provider or "kokoro"
 
+    current_app.logger.info(
+        "[preview] provider=%s language=%s speed=%.2f profile=%s formula=%s",
+        resolved_provider, language, speed, profile_name or "-", formula or "-",
+    )
+
     profiles = load_profiles()
     if resolved_provider == "supertonic" and not profile_name:
         voice_spec = str(payload.get("voice") or payload.get("supertonic_voice") or "M1").strip() or "M1"
@@ -185,7 +207,7 @@ def api_voice_profiles_preview() -> ResponseReturnValue:
             speed = float(normalized_entry.get("speed") or speed)
         else:
             voice_spec = formula_from_profile(normalized_entry) or ""
-            language = str(normalized_entry.get("language") or language)
+            language = _parse_language(normalized_entry.get("language") or language)
     elif formula:
         voice_spec = formula
         resolved_provider = "kokoro"
@@ -197,7 +219,13 @@ def api_voice_profiles_preview() -> ResponseReturnValue:
         voice_spec = formula_from_profile(normalized_entry) or ""
         resolved_provider = "kokoro"
 
+    current_app.logger.info(
+        "[preview] resolved: provider=%s voice_spec=%s",
+        resolved_provider, voice_spec[:80] if voice_spec else "-",
+    )
+
     if not voice_spec:
+        current_app.logger.warning("[preview] empty voice_spec, returning 400")
         return jsonify({"error": "Unable to resolve preview voice"}), 400
 
     try:
@@ -212,6 +240,7 @@ def api_voice_profiles_preview() -> ResponseReturnValue:
             max_seconds=max_seconds,
         )
     except Exception as exc:
+        current_app.logger.exception("[preview] synthesis failed: %s", exc)
         return jsonify({"error": str(exc)}), 500
 
 @api_bp.post("/speaker-preview")
@@ -220,7 +249,7 @@ def api_speaker_preview() -> ResponseReturnValue:
     pending_id = str(payload.get("pending_id") or "").strip()
     text = payload.get("text", "Hello world")
     voice = payload.get("voice", "af_heart")
-    language = payload.get("language", "a")
+    language = _parse_language(payload.get("language"))
     speed_value = payload.get("speed")
     speed = coerce_float(speed_value, 1.0)
     tts_provider = str(payload.get("tts_provider") or "").strip().lower()
@@ -230,7 +259,7 @@ def api_speaker_preview() -> ResponseReturnValue:
     use_gpu = settings.get("use_gpu", False)
 
     base_spec, speaker_name = split_profile_spec(voice)
-    resolved_provider = tts_provider if tts_provider in {"kokoro", "supertonic"} else ""
+    resolved_provider = tts_provider if is_plugin_registered(tts_provider) else ""
 
     if speaker_name:
         entry = normalize_profile_entry(load_profiles().get(speaker_name))
@@ -280,83 +309,7 @@ def api_speaker_preview() -> ResponseReturnValue:
 # --- Integration Routes ---
 
 
-def _opds_metadata_overrides(metadata_payload: Mapping[str, Any]) -> Dict[str, Any]:
-    metadata_overrides: Dict[str, Any] = {}
-
-    def _stringify_metadata_value(value: Any) -> str:
-        if value is None:
-            return ""
-        if isinstance(value, (list, tuple, set)):
-            parts = [str(item).strip() for item in value if item is not None]
-            parts = [part for part in parts if part]
-            return ", ".join(parts)
-        return str(value).strip()
-
-    raw_series = metadata_payload.get("series") or metadata_payload.get("series_name")
-    series_name = str(raw_series or "").strip()
-    if series_name:
-        metadata_overrides["series"] = series_name
-        metadata_overrides.setdefault("series_name", series_name)
-
-    series_index_value = (
-        metadata_payload.get("series_index")
-        or metadata_payload.get("series_position")
-        or metadata_payload.get("series_sequence")
-        or metadata_payload.get("book_number")
-    )
-    if series_index_value is not None:
-        series_index_text = str(series_index_value).strip()
-        if series_index_text:
-            metadata_overrides.setdefault("series_index", series_index_text)
-            metadata_overrides.setdefault("series_position", series_index_text)
-            metadata_overrides.setdefault("series_sequence", series_index_text)
-            metadata_overrides.setdefault("book_number", series_index_text)
-
-    tags_value = metadata_payload.get("tags") or metadata_payload.get("keywords")
-    if tags_value:
-        tags_text = _stringify_metadata_value(tags_value)
-        if tags_text:
-            metadata_overrides.setdefault("tags", tags_text)
-            metadata_overrides.setdefault("keywords", tags_text)
-            metadata_overrides.setdefault("genre", tags_text)
-
-    description_value = metadata_payload.get("description") or metadata_payload.get("summary")
-    if description_value:
-        description_text = _stringify_metadata_value(description_value)
-        if description_text:
-            metadata_overrides.setdefault("description", description_text)
-            metadata_overrides.setdefault("summary", description_text)
-
-    subtitle_value = (
-        metadata_payload.get("subtitle")
-        or metadata_payload.get("sub_title")
-        or metadata_payload.get("calibre_subtitle")
-    )
-    if subtitle_value:
-        subtitle_text = _stringify_metadata_value(subtitle_value)
-        if subtitle_text:
-            metadata_overrides.setdefault("subtitle", subtitle_text)
-
-    publisher_value = metadata_payload.get("publisher")
-    if publisher_value:
-        publisher_text = _stringify_metadata_value(publisher_value)
-        if publisher_text:
-            metadata_overrides.setdefault("publisher", publisher_text)
-
-    # Author mapping: Abogen templates look for either 'authors' or 'author'.
-    authors_value = (
-        metadata_payload.get("authors")
-        or metadata_payload.get("author")
-        or metadata_payload.get("creator")
-        or metadata_payload.get("dc_creator")
-    )
-    if authors_value:
-        authors_text = _stringify_metadata_value(authors_value)
-        if authors_text:
-            metadata_overrides.setdefault("authors", authors_text)
-            metadata_overrides.setdefault("author", authors_text)
-
-    return metadata_overrides
+from abogen.domain.metadata_overrides import normalize_opds_metadata as _opds_metadata_overrides
 
 @api_bp.get("/integrations/calibre-opds/feed")
 def api_calibre_opds_feed() -> ResponseReturnValue:
@@ -651,7 +604,7 @@ def api_entity_pronunciation_preview() -> ResponseReturnValue:
     token = payload.get("token", "").strip()
     pronunciation = payload.get("pronunciation", "").strip()
     voice = payload.get("voice", "").strip()
-    language = payload.get("language", "a").strip()
+    language = _parse_language(payload.get("language"))
     
     if not token and not pronunciation:
         return jsonify({"error": "Token or pronunciation required"}), 400

abogen/webui/routes/jobs.py

@@ -8,8 +8,10 @@ from flask.typing import ResponseReturnValue
 
 from abogen.webui.service import (
     JobStatus,
-    load_audiobookshelf_chapters,
+)
+from abogen.domain.metadata_helpers import (
     build_audiobookshelf_metadata,
+    load_audiobookshelf_chapters,
 )
 from abogen.webui.routes.utils.service import get_service
 from abogen.webui.routes.utils.form import render_jobs_panel
@@ -19,18 +21,25 @@ from abogen.webui.routes.utils.epub import (
     locate_job_epub,
     locate_job_audio,
 )
-from abogen.webui.routes.utils.settings import (
-    stored_integration_config,
+from abogen.domain.settings_core import (
     build_audiobookshelf_config,
-    coerce_bool,
+    stored_integration_config,
 )
 from abogen.webui.routes.utils.common import existing_paths
-from abogen.integrations.audiobookshelf import AudiobookshelfClient, AudiobookshelfUploadError
+from abogen.infrastructure.exporters import ExportService
 
 logger = logging.getLogger(__name__)
 
 jobs_bp = Blueprint("jobs", __name__)
 
+
+def _resolve_cover(job: Any, config: Any) -> Optional[Path]:
+    """Resolve cover image path if enabled."""
+    if not config.send_cover or not job.cover_image_path:
+        return None
+    cover = job.cover_image_path if isinstance(job.cover_image_path, Path) else Path(str(job.cover_image_path))
+    return cover if cover.exists() else None
+
 @jobs_bp.get("/<job_id>")
 def job_detail(job_id: str) -> ResponseReturnValue:
     job = get_service().get_job(job_id)
@@ -98,24 +107,18 @@ def send_job_to_audiobookshelf(job_id: str) -> ResponseReturnValue:
         return _panel_response()
 
     settings = stored_integration_config("audiobookshelf")
-    if not settings or not coerce_bool(settings.get("enabled"), False):
+    if not settings or not settings.get("enabled"):
         job.add_log("Audiobookshelf upload skipped: integration is disabled.", level="warning")
         service._persist_state()
         return _panel_response()
 
     config = build_audiobookshelf_config(settings)
     if config is None:
-        job.add_log(
-            "Audiobookshelf upload skipped: configure base URL, API token, and library ID first.",
-            level="warning",
-        )
+        job.add_log("Audiobookshelf upload skipped: configure base URL, API token, and library ID first.", level="warning")
         service._persist_state()
         return _panel_response()
     if not config.folder_id:
-        job.add_log(
-            "Audiobookshelf upload skipped: enter the folder name or ID in the Audiobookshelf settings.",
-            level="warning",
-        )
+        job.add_log("Audiobookshelf upload skipped: enter the folder name or ID in the Audiobookshelf settings.", level="warning")
         service._persist_state()
         return _panel_response()
 
@@ -125,39 +128,20 @@ def send_job_to_audiobookshelf(job_id: str) -> ResponseReturnValue:
         service._persist_state()
         return _panel_response()
 
-    cover_path = None
-    if config.send_cover and job.cover_image_path:
-        cover_candidate = job.cover_image_path
-        if not isinstance(cover_candidate, Path):
-            cover_candidate = Path(str(cover_candidate))
-        if cover_candidate.exists():
-            cover_path = cover_candidate
-
-    subtitles = existing_paths(job.result.subtitle_paths) if config.send_subtitles else None
-    chapters = load_audiobookshelf_chapters(job) if config.send_chapters else None
-    metadata = build_audiobookshelf_metadata(job)
-    display_title = metadata.get("title") or audio_path.stem
     overwrite_requested = request.form.get("overwrite") == "true" or request.args.get("overwrite") == "true"
 
+    if not overwrite_requested:
+        from abogen.integrations.audiobookshelf import AudiobookshelfClient, AudiobookshelfUploadError
+        metadata = build_audiobookshelf_metadata(job)
+        display_title = metadata.get("title") or audio_path.stem
         try:
-        client = AudiobookshelfClient(config)
-    except ValueError as exc:
-        job.add_log(f"Audiobookshelf configuration error: {exc}", level="error")
-        service._persist_state()
-        return _panel_response()
-
-    try:
-        existing_items = client.find_existing_items(display_title, folder_id=config.folder_id)
+            existing_items = AudiobookshelfClient(config).find_existing_items(display_title, folder_id=config.folder_id)
         except AudiobookshelfUploadError as exc:
             job.add_log(f"Audiobookshelf lookup failed: {exc}", level="error")
             service._persist_state()
             return _panel_response()
-
-    if existing_items and not overwrite_requested:
-        job.add_log(
-            f"Audiobookshelf already contains '{display_title}'. Awaiting overwrite confirmation.",
-            level="warning",
-        )
+        if existing_items:
+            job.add_log(f"Audiobookshelf already contains '{display_title}'. Awaiting overwrite confirmation.", level="warning")
             service._persist_state()
             if request.headers.get("HX-Request"):
                 detail = {
@@ -171,37 +155,22 @@ def send_job_to_audiobookshelf(job_id: str) -> ResponseReturnValue:
                 return Response("", status=204, headers=headers)
             return _panel_response()
 
-    if existing_items and overwrite_requested:
-        try:
-            client.delete_items(existing_items)
-        except AudiobookshelfUploadError as exc:
-            job.add_log(f"Audiobookshelf overwrite aborted: {exc}", level="error")
-            service._persist_state()
-            return _panel_response()
-        else:
-            job.add_log(
-                f"Removed {len(existing_items)} existing Audiobookshelf item(s) prior to overwrite.",
-                level="info",
-            )
-
     job.add_log("Audiobookshelf upload triggered manually.", level="info")
+    export_svc = ExportService()
     try:
-        client.upload_audiobook(
+        export_svc.upload_audiobookshelf(
+            job,
             audio_path,
-            metadata=metadata,
-            cover_path=cover_path,
-            chapters=chapters,
-            subtitles=subtitles,
+            existing_paths(job.result.subtitle_paths),
+            load_audiobookshelf_chapters(job) if config.send_chapters else None,
+            build_audiobookshelf_metadata(job),
+            cover_path=_resolve_cover(job, config),
+            config=config,
+            log_callback=lambda msg, lvl="info": job.add_log(msg, level=lvl),
         )
-    except AudiobookshelfUploadError as exc:
-        job.add_log(f"Audiobookshelf upload failed: {exc}", level="error")
     except Exception as exc:
         job.add_log(f"Audiobookshelf integration error: {exc}", level="error")
-    else:
-        job.add_log("Audiobookshelf upload queued.", level="success")
-    finally:
     service._persist_state()
-
     return _panel_response()
 
 @jobs_bp.post("/clear-finished")