[Libav-user] avcodec_open2 is changing the channels and channel_layout... why?

Michael Bradshaw mbradshaw at sorensonmedia.com
Fri Oct 12 01:19:31 CEST 2012

On Thu, Oct 11, 2012 at 5:15 PM, Carl Eugen Hoyos <cehoyos at ag.or.at> wrote:
> Michael Bradshaw <mbradshaw at ...> writes:
>> QuickTime reports it as mono. So does Windows Media Player. It plays
>> ok in ffplay and QuickTime though (didn't try Windows Media Player).
>> Seeing as remuxing the audio stream to plain .aac seems to have fixed
>> the issue, I'm thinking the container might be bad. Do you know of any
>> tools or options in ffmpeg to help validate that conclusion?
> I would say you just have to open out.aac in QuickTime
> or am I wrong?

Actually, I just tried ffmpeg -i ~/MP4-Apple264-AACPlus.mp4 -acodec
copy -vcodec copy ~/out.mp4 and it generated a .mp4 with the same
issue (that is, ffprobe -show_streams reports the audio stream as
having 1 channel, whereas the dump and show_frames reports 2
channels). I get the same thing if I also do ./ffmpeg -i
~/MP4-Apple264-AACPlus.mp4 -acodec copy -vn ~/out.mp4

Why would ffmpeg generate an .mp4 with the same issue? I think it's
weird because if I just remux the audio alone to a .aac it works fine
in ffprobe, but if I remux it into .mp4 it has the same problems.

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