[FFmpeg-devel] Channel layouts

Nicolas George nicolas.george at normalesup.org
Sun Nov 11 23:53:39 CET 2012

Le primidi 21 brumaire, an CCXXI, Carl Eugen Hoyos a écrit :
> But the current problem imo is that ffmpeg invents a layout 
> if it is unknown and even if it unsupported (making it 
> impossible for the user / caller to understand what is 
> going wrong), see tickets #1763, #1764.

That is true, that is a misfeature. It is necessary because of lavfi's
current design. I have proposed a workaround for that.

> (I can't comment on the TrueHD issue, but files can 
> obviously have different channel counts and 
> incorrectly written layouts, and looking at ticket 

It is not how I understand the code: the file looks like dual-mono, reported
as 2-channels and mono. That is not how the API is supposed to work, but it
is not absurd at all.

> #1819, I wonder if it may be perfectly valid for 
> some isom files to show stereo for mono files.)

I do not have time to read the whole ticket right now, but if it is valid,
then it is another proof that isom is braindead. And as usual with badly
designed and braindead formats, the only thing to do is to make the best of
it while still returning something sensical.

> I'd like to point out that afaik we have no sample 
> that cannot be correctly described by wav-channel 
> layout, we just have bugs.

What about dual-mono files? Granted, they are almost never correctly flagged
as such, and almost always passed as stereo, but if I understand correctly
the truhd sample the trend is changing.


  Nicolas George
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