[FFmpeg-devel] [PATCH] lavf/mov: ignore edit list with duration equals to 0 for covers art

[Matthieu Bouron]

On Thu, Jan 19, 2017 at 04:55:22AM +0900, Yusuke Nakamura wrote:
> 2017-01-18 19:38 GMT+09:00 Matthieu Bouron <matthieu.bouron at gmail.com>:
> 
> > Discards edit list with duration equals to 0 for video streams with only
> > one frame and avoid discarding covers art muxed as a single frame video
> > stream.
> > ---
> > Hello,
> >
> > The following patch discards single edit list with duration equals to 0
> > for video streams with only one frame which prevents discarding covers art
> > muxed as a single frame video stream.
> >
> > The patch can be extended to make it always discards single edit list with
> > duration equals to 0 (even if the video streams has more than one sample).
> > What do you think ?
> >
> > Matthieu
> > ---
> >  libavformat/mov.c | 11 +++++++++++
> >  1 file changed, 11 insertions(+)
> >
> > diff --git a/libavformat/mov.c b/libavformat/mov.c
> > index d1b929174d..88ffd0e5f2 100644
> > --- a/libavformat/mov.c
> > +++ b/libavformat/mov.c
> > @@ -2988,6 +2988,17 @@ static void mov_fix_index(MOVContext *mov, AVStream
> > *st)
> >      if (!msc->elst_data || msc->elst_count <= 0 || nb_old <= 0) {
> >          return;
> >      }
> > +
> > +    // Discard edit list with duration equals to 0 for video streams with
> > only
> > +    // one frame and avoid discarding covers art muxed as a single frame
> > video
> > +    // stream
> > +    if (st->codecpar->codec_type == AVMEDIA_TYPE_VIDEO &&
> > +        msc->chunk_count == 1 &&
> > +        msc->elst_count == 1 &&
> > +        msc->elst_data[0].duration == 0) {
> >
> 
> This can be false positive since segment_duration=0 could be used for
> implicit segment_duration when movie fragments. The spec explicitly says
> that only when initial movie has no samples but
> w16161-14496-12-DefectReport-R4.docx implies that the 14496-12 spec will
> also apply it to more generic cases. And why msc->chunk_count == 1?  The
> chunk_count is the number of chunks but not samples.
> 

If I understand correctly segment_duration=0 means implicit duration for
all cases (fragmented / non-fragmented) ?  Does that mean we should
discard the duration but honor the rest of the elst fields ?

Regarding the use of msc->chunk_count I wrongly assumed that one chunk ==
one video frame. I used originally st->nb_index_entries but I'm not sure
if it's right though.

Thanks,
Matthieu

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