[linux-dvb] Re: Lipsync

[Tomi Ollila <tomi.ollila@iki.fi>]

Thursday Sep 25 13:57:04 +0200 2003 Johannes Stezenbach <js@convergence.de> wrote:
> Dennis Noordsij wrote:
> > 
> > I am having audio/video sync problems on specific channels, both live viewing 
> > and playing back a recording. It only happens on channels MTV3 and SubTV 
> > which are on the same mux, not on any other muxes. It does not happen all the 
> > time, although certain programs are always problematic.

What programs -- I could give those a try.

> > 
> > If I'd have to isolate a difference (all DVB-T muxes, all same settings apart 
> > from frequency) it is that those channels sometimes have 48kHz audio whereas 
> > the others seem to stick with 44.1kHz.
> > 
> > Using dvb-kernel under 2.4.22, both an older CVS (~ 10 days old) and a recent 
> > one yesterday, same thing.  VDR 1.2.5. Primary card is a Siemens DVB-C 
> > revision 1.5 without a signal (no ves1820 module loaded, no problems 
> > whatsoever with the arm) and tuner card is a Hauppauge Nova-T ("new" model).
> 
> AV7110 based cards support PES playback only, and thus have to rely on the audio
> and video PTS (presentation time stamps) only for lipsync. You'd have to
> check if the PTS of audio and video are there, and are within certain
> limits for the sync to work. If the stream is too badly muxed it will
> play async. I don't know any tool to check this, maybe the Metzler Bros.
> mpegtools can do it.

I briefly checked dvb-mpegtools in libdvb-0.5.0 and did not find anything
that could do that.

I'd suggest try playing the material using mplayer (and on monitor, not via
TV-out of dvb card (well test first with monitor). If that is in sync, the
source material is just too bad (and I don't think any combination of
kernel/dvb-driver fixes that).

You can also try `mencoder -oac copy -ovc copy <inputfile> -o /dev/null'
and see how often it displays `skipped frame' and/or `duplicate frame' 
-- is you get lot of these, it could also explain the problem.


Something closely on-topic: I have one 2 hour recording (done using
dvbstream); When playing using mplayer, it keeps sync all the time.

If I do `dvb-mplex -T MPEG2 -o remux.mpg orig.mpg' with that file, In the
beginning of recording, there is perfect lip-sync. After one hour, video
is about 600ms ahead of audio, and at the end, video is about 700ms ahead
of audio. 

With the above mencoder run, during first hour it often prints `1 duplicate frame',
and near the end some more `1 duplicate frame's... mencoder (in streamcopy
modes) also produced (.avi) file that plays in sync (with mplayer), but
there might be some tricks involved...

> 
> 
> Johannes
> 

Tomi


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