I have an unusual problem that I hope someone can help me solve. I have 45 video files that I'm batch encoding as MP4. Some of those files have their audio channel position set to Front L R and others have have it set to Front C. However, the distribution system which these videos are sent to (and which I have no control over) does some re-processing of these videos. All the videos that have their Channel Position set to Front C are coming back with distorted audio.

My question is:

Does anyone know how to encode a video with ffmpeg and force the audio channel positions to be Front L R? (I have carefully studied this page (https://trac.ffmpeg.org/wiki/AudioChannelManipulation#monostereo) but it was not obvious what the solution might be)

Thank you!

  • The encoder will set stereo layout when you encode with -ac 2 as shown in the wiki you linked to.
    – Gyan
    Dec 12, 2016 at 18:54
  • @Mulvya Thank you, I tried your suggestion. After encoding ffmpeg reported the following for the audio information: "Stream #0:1(und): Audio: aac (LC) (mp4a / 0x6134706D), 44100 Hz, stereo, fltp, 128 kb/s (default)" It's not clear to me how to read this. Does LC mean "Left Channel"?
    – d13
    Dec 12, 2016 at 19:40
  • No. LC means Low Complexity and refers to the audio bitstream profile.
    – Gyan
    Dec 12, 2016 at 19:49

1 Answer 1


If you run ffmpeg -layouts, you will see that stereo indicates the presence of two channels, one assigned as Front Left and the other as Front Right. If you use -ac 2 in your encode, ffmpeg will create a stereo layout output by default. FFmpeg does not display the individual channel assignments in the readout of the file.


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