Update utils/ffmpeg.py

utils/ffmpeg.py

@@ -47,6 +47,6 @@ def ffmpeg(input_stream: io.BufferedReader, ffmpeg_args: list) -> io.BytesIO:
 def mp3_to_opus(input_bytes_io: io.BytesIO) -> io.BytesIO:
     try:
         input_stream = io.BufferedReader(input_bytes_io)
-        return ffmpeg(input_stream, ["-c:a", "libopus"])
+        return ffmpeg(input_stream, ["-c:a", "libopus", "-f", "opus"])
     except Exception as e:
         raise RuntimeError(f"Failed to convert MP3 to Opus: {str(e)}")