[FFmpeg-devel] [Bugreport] and [Patch]: duration of TS streams is wrong when used near 2^33 wrap

[Michael Niedermayer]

Hi

On Mon, Oct 29, 2007 at 10:40:29AM -0000, M?ns Rullg?rd wrote:
> 
> Thorsten Jordan wrote:
> > Hello,
> >
> > in libavformat/utils.c, the function av_estimate_timings_from_pts() is
> > used also for TS streams. It seeks to begin of file and gets a PTS value
> >  from a stream's packet and one value from the end.
> > It then computes:
> >
> > line 1559ff:
> > ***snip***
> > 	...
> >             end_time = pkt->pts;
> >             duration = end_time - st->start_time;
> >             if (duration > 0) {
> > 	...
> > ***snap***
> >
> > now for TS the PTS values are wrapping around at 2^33, so if the start
> > pts is near 2^33 and the end pts is beyond it, end < start is true
> > trivially, leading to no computed duration.
> >
> > How to fix that?
> >
> > e.g.: compute duration = (2^33 + end - start) & (2^33-1)
> >
> > pro: works for this and similar files
> > con: would give still wrong values if the file is longer than 2^33 pts
> > (26.5 hours), but rare case
> 
> It would fail also if the file has random PTS resets, as is quite common
> on DVDs and some TV channels.
> 
> > it would not hurt for PS streams, as for PS the PTS is max. 2^32 iirc.
> 
> PS also uses 33-bit PTS.
> 
> > The attached patch does that.
> 
> I think this is a problem we shouldn't even be trying to solve.  If you
> really must know the exact duration of the file you'll have to parse
> the whole thing.
> 
> I'm inclined to say that rather than trying to guess the unknown, we should
> simply report the duration of these files as unknown.

yes, fully agree


[...]
-- 
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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