[FFmpeg-devel] PTS/DTS inaccuracy in PES

[Michael Niedermayer]

On Tue, Jan 06, 2009 at 05:56:05PM +0200, Tomer Barletz wrote:
> On Tue, Jan 6, 2009 at 4:57 PM, Michael Niedermayer <michaelni at gmx.at> wrote:
> > On Tue, Jan 06, 2009 at 08:44:57AM +0200, Tomer Barletz wrote:
> >> Hi Michael,
> >>
> >> On Mon, Jan 5, 2009 at 8:25 PM, Michael Niedermayer <michaelni at gmx.at> wrote:
> >> > On Mon, Jan 05, 2009 at 06:15:57PM +0200, Tomer Barletz wrote:
> >> >> Hi  everyone,
> >> >> Lately I've been working on the TS muxer from the gsoc repository, in
> >> >> order to fix some PCR timing issues.
> >> >> I've submitted a patch to fix these issues, and the output TS looks
> >> >> nice and accurate now.
> >> >>
> >> >> However, I'm currently experiencing some problems with the (video) PES
> >> >> PTS/DTS accuracy.
> >> >> After analysing the PES, I can see significant irregularities with the
> >> >> stream - the PTS and DTS values looks correct at first, but they will
> >> >> lose accuracy exponentially very soon.
> >> >>
> >> >> I've started to look at the code, and figured that the location where
> >> >> these values are calculated is at
> >> >> libavformat/utils.c::compute_pkt_fields; but this method is quite
> >> >> difficult to understand, specifically the blocks starting at 837, and
> >> >> 877 (I don't want to paste the code here, since it's pretty long).
> >> >> Can someone please shed some light on this?
> >> >
> >> > compute_pkt_fields() is used on the demuxer side, not the muxer.
> >> >
> >> > Also keep in mind H264 in MPEG-* is not supported. We are lacking
> >> > correct timestamp interpolation as described in H.222 & 264!
> >> > So if your problems are with H264 (you didnt say which codec) then
> >> > the problem is near certainly there.
> >> > If it is H264, the fix is to fix the AVParser for H.264 and
> >> > compute_pkt_fields() in the way its decribed in H.222/264 ...
> > [...]
> >> >From your message, I understand that MPEG-2 video is supported.
> >> But yet, I see the same results when wrapping it in a PES.
> >
> > well, you should elaborate on what exactly is wrong and provide some
> > test sample or if its reproduceabel with any pick one already on mphq
> > so we have the same sample ...
[...]
> 
> The following file was created with the "new" TS muxer:
> http://rapidshare.com/files/180404351/test.ts.html
> 
> It was transcoded from a VC-1 stream, using the following command line
> (latest svn):
> ffmpeg -i Coral_Reef_Adventure.wmv -vcodec mpeg2video -s 720x480
> -aspect 4:3 -b 5000k -maxrate 5000k -minrate 5000k -r 29.97 -bufsize
> 1835008 -threads 2 -an test.ts
> 
> As I said before - ffplay/mplayer will play this file with no
> complaints, even though it is not MPEG compliant (inaccurate PTS/DTS
> values).

so the problem only happens with PES in TS but not PES in PS ?

[...]

-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

Republics decline into democracies and democracies degenerate into
despotisms. -- Aristotle
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