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

[Michael Bradshaw]

On Thu, Oct 11, 2012 at 5:19 PM, Michael Bradshaw
<mbradshaw at sorensonmedia.com> wrote:
>[...]
> 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.

Would it matter if the AAC stream is HE-AAC? I can provide the sample
if necessary.