add option to set audio channels directly

README.md

@@ -295,6 +295,8 @@ For more information on the options (`[options]`) available, run `ffmpeg-normali
 
     Will use input sample rate by default, except for EBU normalization, which will change the input sample rate to 192 kHz.
 
+- `-ac`, `--audio-channels`: Set the number of audio channels. If not specified, the input channel layout will be used. This is equivalent to `-ac` in ffmpeg.
+
 - `-koa, --keep-original-audio`: Copy original, non-normalized audio streams to output file
 
 - `-prf PRE_FILTER, --pre-filter PRE_FILTER`: Add an audio filter chain before applying normalization.

ffmpeg_normalize/__main__.py

@@ -303,6 +303,17 @@ def create_parser() -> argparse.ArgumentParser:
         """
         ),
     )
+    group_acodec.add_argument(
+        "-ac",
+        "--audio-channels",
+        type=int,
+        help=textwrap.dedent(
+            """\
+        Set the number of audio channels.
+        If not specified, the input channel layout will be used.
+        """
+        ),
+    )
     group_acodec.add_argument(
         "-koa",
         "--keep-original-audio",
@@ -506,6 +517,7 @@ def _split_options(opts: str) -> list[str]:
         audio_codec=cli_args.audio_codec,
         audio_bitrate=cli_args.audio_bitrate,
         sample_rate=cli_args.sample_rate,
+        audio_channels=cli_args.audio_channels,
         keep_original_audio=cli_args.keep_original_audio,
         pre_filter=cli_args.pre_filter,
         post_filter=cli_args.post_filter,

ffmpeg_normalize/_ffmpeg_normalize.py

@@ -63,6 +63,7 @@ class FFmpegNormalize:
         audio_codec (str, optional): Audio codec. Defaults to "pcm_s16le".
         audio_bitrate (float, optional): Audio bitrate. Defaults to None.
         sample_rate (int, optional): Sample rate. Defaults to None.
+        audio_channels (int | None, optional): Audio channels. Defaults to None.
         keep_original_audio (bool, optional): Keep original audio. Defaults to False.
         pre_filter (str, optional): Pre filter. Defaults to None.
         post_filter (str, optional): Post filter. Defaults to None.
@@ -98,6 +99,7 @@ def __init__(
         audio_codec: str = "pcm_s16le",
         audio_bitrate: float | None = None,
         sample_rate: float | int | None = None,
+        audio_channels: int | None = None,
         keep_original_audio: bool = False,
         pre_filter: str | None = None,
         post_filter: str | None = None,
@@ -170,6 +172,7 @@ def __init__(
         self.dual_mono = dual_mono
         self.dynamic = dynamic
         self.sample_rate = None if sample_rate is None else int(sample_rate)
+        self.audio_channels = None if audio_channels is None else int(audio_channels)
 
         self.audio_codec = audio_codec
         self.audio_bitrate = audio_bitrate

ffmpeg_normalize/_media_file.py

@@ -355,6 +355,8 @@ def _second_pass(self) -> Iterator[float]:
             cmd.extend(["-b:a", str(self.ffmpeg_normalize.audio_bitrate)])
         if self.ffmpeg_normalize.sample_rate:
             cmd.extend(["-ar", str(self.ffmpeg_normalize.sample_rate)])
+        if self.ffmpeg_normalize.audio_channels:
+            cmd.extend(["-ac", str(self.ffmpeg_normalize.audio_channels)])
 
         # ... and subtitles
         if not self.ffmpeg_normalize.subtitle_disable:

test/test.py

@@ -460,3 +460,18 @@ def test_quiet(self):
             ["test/test.mp4", "-ext", "wav", "-vn", "-f", "q"]
         )
         assert "only supports one stream" not in stderr
+
+    def test_audio_channels(self):
+        ffmpeg_normalize_call(
+            ["test/test.mp4", "-ac", "1", "-o", "normalized/test.wav"]
+        )
+        assert os.path.isfile("normalized/test.wav")
+        stream_info = _get_stream_info("normalized/test.wav")[0]
+        assert stream_info["channels"] == 1
+
+        ffmpeg_normalize_call(
+            ["test/test.mp4", "-ac", "2", "-o", "normalized/test2.wav"]
+        )
+        assert os.path.isfile("normalized/test2.wav")
+        stream_info = _get_stream_info("normalized/test2.wav")[0]
+        assert stream_info["channels"] == 2