diff --git a/abogen/conversion.py b/abogen/conversion.py
index d1ee171..f4084aa 100644
--- a/abogen/conversion.py
+++ b/abogen/conversion.py
@@ -519,7 +519,7 @@ class ConversionThread(QThread):
                                 "-ac",
                                 "1",
                                 "-i",
-                                "pipe:",
+                                "pipe:0",
                                 "-c:a",
                                 "libopus",
                                 "-b:a",
@@ -598,7 +598,7 @@ class ConversionThread(QThread):
                     ffmpeg_cmd_opus = [
                         "ffmpeg", "-y",
                         "-thread_queue_size", "1024", # Increased thread_queue_size
-                        "-f", "f32le", "-ar", "24000", "-ac", "1", "-i", "pipe:",
+                        "-f", "f32le", "-ar", "24000", "-ac", "1", "-i", "pipe:0",
                         "-c:a", "libopus", "-b:a", "24000", # Original bitrate
                         opus_out_path,
                     ]
diff --git a/abogen/utils.py b/abogen/utils.py
index 63e4ffe..6536102 100644
--- a/abogen/utils.py
+++ b/abogen/utils.py
@@ -118,8 +118,10 @@ def create_process(cmd, stdin=None, text=True):
         root.addHandler(handler)
         root.setLevel(logging.INFO)
     
+    # Determine shell usage: use shell only for string commands
+    use_shell = isinstance(cmd, str)
     kwargs = {
-        "shell": True,
+        "shell": use_shell,
         "stdout": subprocess.PIPE,
         "stderr": subprocess.STDOUT,
         "bufsize": 1,  # Line buffered