[FFmpeg-devel] [PATCH] avformat/matroskaenc: always reserve max aac private data

[John Stebbins]

On Fri, 2020-05-01 at 20:10 +0200, Nicolas George wrote:
> John Stebbins (12020-05-01):
> > If the parameters change on the fly, some part of the audio stream
> > is
> > going to be unplayable.  Either the part after the change will be
> > unplayable if you ignore extradata changes, or everything
> > preceeding 
> > the last extradata change will be unplayable if you rewrite codec
> > private on every change.
> 
> Then the only acceptable solution is to report an error.
> 
> If we can detect that the new extradata is compatible and will not
> cause
> the file to be unplayable, we can let it pass, but we should try to
> NEVER allow to lose data without notifying users.
> 

Well, current code in aac_adtstoasc silently ignores any changes.  It
only generates extradata from the initial packet.  It's not checked in
subsequent packets.

So this would have to be "fixed" in aac_adtstoasc as well if you want
to add error logging.

This is also a bit beyond my expertise.  I don't know what would
constitute incompitible parameters beyond a few obvious things.  I'm
not well versed in aac details.