[FFmpeg-devel] [PATCH] mov.c: read fragment start dts from fragmented mp4

[Yusuke Nakamura]

2014-10-10 4:49 GMT+09:00 Michael Niedermayer <michaelni at gmx.at>:

> On Thu, Oct 09, 2014 at 09:44:43PM +0200, Michael Niedermayer wrote:
> > On Thu, Oct 09, 2014 at 06:57:59PM +0300, Mika Raento wrote:
> > > If present, an MFRA box and its TFRAs are read for fragment start
> times.
> > >
> > > Without this change, timestamps for discontinuous fragmented mp4 are
> > > wrong, and cause audio/video desync and are not usable for generating
> > > HLS.
> > > ---
> > >  libavformat/isom.h |  15 ++++++
> > >  libavformat/mov.c  | 140
> +++++++++++++++++++++++++++++++++++++++++++++++++++++
> > >  2 files changed, 155 insertions(+)
> >
> > this seems to break some files
> >
> > for example a file generated with the following 2 commands:
> > ffmpeg -i matrixbench_mpeg2.mpg -t 10 in.mp4
> > l-smash/cli/remuxer -i in.mp4 --fragment 1 -o test.mp4
> >
> > ive not investigated why this doesnt work
>
> maybe above was unclear, so to clarify before someone is confused
> test.mp4 from above plays with ffplay before te patch but not really
> aferwards. The 2 commads are just to create such file
>
> [...]
>
> --
> Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB
>
> Good people do not need laws to tell them to act responsibly, while bad
> people will find a way around the laws. -- Plato
>
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>
The 'time' field in the tfra box is defined in presentation timeline, not
composition or decode timeline.
Therefore, generally, the value of 'time' can't be used for DTS directly as
long as following 14496-12.
Maybe some derivatives of ISO Base Media file format define differently,
but the spec of ISO Base Media file format defines 'time' as the
presentation time of the sync sample.
Presentation times are composition times after the application of any edit
list for the track.

I have also some samples which use the 'time' as DTS of sync sample.
Historically, the term 'presentation time' was not defined clearly before
14496-12:2012, this fact possibly may have brought about such inconsistency.