diff --git a/CHANGELOG.md b/CHANGELOG.md
index 73fb97b..65dc9e8 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,4 +1,5 @@
 # 1.1.3 (pre-release)
+- `M4B (with chapters)` generation is not faster now, as it directly generates `m4b` files instead of converting from `wav`, which significantly reduces processing time.
 - Better sleep state handling for Linux.
 - Fixed issue where the app would not restart properly on Windows.
 - Fixed last sentence/subtitle entry timing in generated subtitles, the end time of the final subtitle entry now correctly matches the end of the audio chunk, preventing zero or invalid timings at the end.
diff --git a/abogen/conversion.py b/abogen/conversion.py
index 8591b65..4f1756c 100644
--- a/abogen/conversion.py
+++ b/abogen/conversion.py
@@ -488,13 +488,27 @@ class ConversionThread(QThread):
                     )
                     ffmpeg_proc = None
                 elif self.output_format == "m4b":
-                    temp_wav_path = os.path.join(
-                        out_dir, f"temp_{base_name}{suffix}.wav"
-                    )
-                    merged_out_file = sf.SoundFile(
-                        temp_wav_path, "w", samplerate=24000, channels=1, format="wav"
-                    )
+                    # Real-time M4B generation using FFmpeg pipe
+                    static_ffmpeg.add_paths()
+                    merged_out_file = None
                     ffmpeg_proc = None
+                    # Prepare ffmpeg command for m4b output
+                    metadata_options = self._extract_and_add_metadata_tags_to_ffmpeg_cmd()
+                    cmd = [
+                        "ffmpeg",
+                        "-y",
+                        "-thread_queue_size", "32768",
+                        "-f", "f32le",
+                        "-ar", "24000",
+                        "-ac", "1",
+                        "-i", "pipe:0",
+                        "-c:a", "aac",
+                        "-q:a", "2",
+                        "-movflags", "+faststart+use_metadata_tags",
+                    ]
+                    cmd += metadata_options
+                    cmd.append(merged_out_path)
+                    ffmpeg_proc = create_process(cmd, stdin=subprocess.PIPE, text=False)
                 elif self.output_format == "opus":
                     static_ffmpeg.add_paths()
                     cmd = [
@@ -912,8 +926,9 @@ class ConversionThread(QThread):
                 if self.output_format in ["wav", "mp3", "flac"]:
                     merged_out_file.close()
                 elif self.output_format == "m4b":
-                    merged_out_file.close()
-                    # Only generate chapters info if there are chapters
+                    ffmpeg_proc.stdin.close()
+                    ffmpeg_proc.wait()
+                    # Add chapters via fast post-processing
                     if total_chapters > 1:
                         chapters_info_path = f"{base_filepath_no_ext}_chapters.txt"
                         with open(chapters_info_path, "w", encoding="utf-8") as f:
@@ -925,63 +940,26 @@ class ConversionThread(QThread):
                                 f.write(f"START={int(chapter['start']*1000)}\n")
                                 f.write(f"END={int(chapter['end']*1000)}\n")
                                 f.write(f"title={chapter_title}\n\n")
-                        metadata_options = (
-                            self._extract_and_add_metadata_tags_to_ffmpeg_cmd()
-                        )
+                        # Fast mux chapters into m4b (write to temp file, then replace original)
                         static_ffmpeg.add_paths()
+                        orig_path = merged_out_path
+                        root, ext = os.path.splitext(orig_path)
+                        tmp_path = root + ".tmp" + ext
                         cmd = [
                             "ffmpeg",
                             "-y",
-                            "-i",
-                            temp_wav_path,
-                            "-i",
-                            chapters_info_path,
-                            "-map",
-                            "0:a",
-                            "-map_metadata",
-                            "1",
-                            "-map_chapters",
-                            "1",
-                            *metadata_options,
-                            "-c:a",
-                            "aac",
-                            "-q:a",
-                            "2",
-                            "-movflags",
-                            "+faststart+use_metadata_tags",
-                            merged_out_path,
+                            "-i", orig_path,
+                            "-i", chapters_info_path,
+                            "-map", "0:a",
+                            "-map_metadata", "1",
+                            "-map_chapters", "1",
+                            "-c:a", "copy",
+                            tmp_path
                         ]
                         proc = create_process(cmd)
                         proc.wait()
-                        self.log_updated.emit(
-                            ("\nCleaning up temporary files...", "grey")
-                        )
-                        if os.path.exists(chapters_info_path):
-                            os.remove(chapters_info_path)
-                    else:
-                        # No chapters: skip chapters info and related ffmpeg args
-                        metadata_options = (
-                            self._extract_and_add_metadata_tags_to_ffmpeg_cmd()
-                        )
-                        static_ffmpeg.add_paths()
-                        cmd = [
-                            "ffmpeg",
-                            "-y",
-                            "-i",
-                            temp_wav_path,
-                            *metadata_options,
-                            "-c:a",
-                            "aac",
-                            "-q:a",
-                            "2",
-                            "-movflags",
-                            "+faststart+use_metadata_tags",
-                            merged_out_path,
-                        ]
-                        proc = create_process(cmd)
-                        proc.wait()
-                    if os.path.exists(temp_wav_path):
-                        os.remove(temp_wav_path)
+                        os.replace(tmp_path, orig_path)
+                        os.remove(chapters_info_path)
                 elif self.output_format in ["opus"]:
                     ffmpeg_proc.stdin.close()
                     ffmpeg_proc.wait()