1

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 '16 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 '16 at 19:40
  • No. LC means Low Complexity and refers to the audio bitstream profile. – Gyan Dec 12 '16 at 19:49
4

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.

| improve this answer | |

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.