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

[Sasi Inguva]

According to  spec ( ISO-IEC-15444-12 ) specifying edit list duration 0,
makes sense for MP4F files
"A non‐empty edit may insert a portion of the media timeline that is not
present in the initial movie, and
is present only in subsequent movie fragments. Particularly in an empty
initial movie of a fragmented
movie file (when there are no media samples yet present), the
segment_duration of this edit may be
zero, whereupon the edit provides the offset from media composition time to
movie presentation time,
for the movie and subsequent movie fragments. It is recommended that such
an edit be used to
establish a presentation time of 0 for the first presented sample, when
composition offsets are used"

I was contacted with such a file previously and I tried playing that  in
Quicktime in mac to see its behavior.  When I played the video with
Quicktime 10.4 it showed the poster frame.  When I played it with Quicktime
7 , it showed black screen. Even in Quicktime 10.4 when you export the
video to reencode it, the output file has only audio.

However your hack seems to be specialized enough, so as not to hurt other
edit list cases. You just need to check that the file is not Fragmented MP4
, and need to check for st->nb_index_entries == 1 instead of
chunk_count==1.

On Thu, Jan 19, 2017 at 1:33 AM, Matthieu Bouron <matthieu.bouron at gmail.com>
wrote:

> 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
>
> [...]
> _______________________________________________
> ffmpeg-devel mailing list
> ffmpeg-devel at ffmpeg.org
> http://ffmpeg.org/mailman/listinfo/ffmpeg-devel
>