[FFmpeg-devel] [PATCH] avformat/mpegts: correct timestamp overflow on multiple pcr loopback

[Sébastien Rossi]

Hi,
Ok, my goal was to eliminate all wraparound for live transport stream
mainly. But as it seems hard to handle this particular case (long live
stream) and cover all the other use cases (scaning, smart stuff etc), I
will keep this patch on my side as an option for my personal usage.
Thanks for your help, have a good day.

Sébastien

Le ven. 24 juin 2022 à 22:35, Michael Niedermayer <michael at niedermayer.cc>
a écrit :

> Hi
>
> On Fri, Jun 24, 2022 at 02:30:19PM +0200, Sébastien Rossi wrote:
> > The issue I tried to patch is that on ts stream that last more than 26,5h
> > (time between pcr loopback) we had pts and dts discontinuities. In
> > wrap_timestamp function in demux.c, I've seen there's some code to
> correct
> > timestamp overflow, but when the stream last more than 26,5h, timestamps
> > are upper than pts_wrap_reference two times. So the second time we outrun
> > the pts_wrap_reference we lose the timestamp correction and have some
> > errors like pts < dts.
> > What I tried to do is to restamp pts and dts using mpegts pcr
> information.
> > The preserve_continuity function checks relative position between
> timestamp
> > (dts or pts) and pcr, and handle cases when pcr have already loopback and
> > timestamp not or vice versa. Then it applicates correction to the
> timestamp
> > depending on pcr loopback count.
>
> there can be more timestamp discontinuities than one per 26.5h
> if the goal is to remove all that requires more code. Either
> some scaning of the whole file or some quite smart stuff and either
> way a buffer to store where the discontinuities are so they are
> consistantly
> handled during seeking.
>
> if the goal is to eliminate 1 wraparound only, there should be some
> existing code i think that does this. IIRC see pts_wrap_behavior
>
> the wraping behavior is applies to multiple demuxers so code
> handling it really does not belong in a single demuxer
>
>
> >
> > I can provide a stream with a duration of 30h, if you want to.
>
> not needed
>
>
> >
> > Could you tell me how to reproduce the segfault you've seen ?
>
> it segfaults because filter is NULL.
> i can send you the file but as the code and why its segfaults is
> specific to one demxuer and this shouldnt be in one single demuxer
> i dont think it would help you
>
> thx
>
> [...]
> --
> Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB
>
> I am the wisest man alive, for I know one thing, and that is that I know
> nothing. -- Socrates
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