[FFmpeg-devel] PTS/DTS inaccuracy in PES

Tomer Barletz barletz
Tue Jan 6 07:44:57 CET 2009

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 ...
> [...]
> --
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>From your message, I understand that MPEG-2 video is supported.
But yet, I see the same results when wrapping it in a PES.

I should also mention that I can play the video correctly using ffplay
or mplayer, but not with VLC or an IP STB.

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