[FFmpeg-devel] Any suggestion about better handling edit list in mov demuxer.

Michael Niedermayer michaelni
Fri May 14 01:22:28 CEST 2010

On Wed, May 12, 2010 at 04:25:19PM -0700, Thierry Foucu wrote:
> On Wed, May 12, 2010 at 8:30 AM, Michael Niedermayer <michaelni at gmx.at>wrote:
> > On Wed, May 12, 2010 at 10:24:50AM +0200, elupus wrote:
> > > >
> > > >    - Adding a flag to AVPacket like DROP_AFTER_DECODER, in which case
> > the
> > > >    demuxer could mark which packet will be needed to be dropped after
> > decoding,
> > > >    and  av_read_frame will still return them to pass them to the
> > decoder.
> > >
> > > This i think is the best aproach. It is something that can be used for
> > > seeking aswell. (and matches very well what we already do in xbmc after
> > > seeks).
> >
> > it will not work with audio as audio is simply not encoded with the
> > same packet rate as video. There would be too much or missing audio.
> > I thus think a solution that can handle sample accuracy and not just
> > packet accuracy is needed
> >
> >
> Agreed, that should the optimal solution. But are we not talking about a
> maximum lipsync problem of 1 audio frame per chunk? which could be less than
> 1 video frame duration?

i dunno about mov but in avi 0.5 second long audio frames are not that
uncommon thats enough to cause problems i think.

but lets first awnser a few questions (i dont know much about edit lists)
it was said that edit lists can ignore keyframes. This alone already looks
problematic, i mean if we have a 300 frame gop and an edit list starts at the
last frame then once this edit list becomes "active" we would have to very
quickly decode 10 seconds of video to show the next frame. This almost
certainly would cause problems to some players no matter how we implement it
So do edit lists in actual files really refer to non keyframes?
Also does the official (qt) player really display that non keyframe or does
it drop things until the next keyframe?
Iam trying to understand better how the actually used cases look because
the generic case is not implementable. (just think of a 2 hour file with
only 1 keyframe at the very begin)

Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

While the State exists there can be no freedom; when there is freedom there
will be no State. -- Vladimir Lenin
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