[linux-dvb] Re: Mplex doesn't work

[Jan Panteltje <root@panteltje.demon.nl>]

On Sat, 2 Jun 2001, Klaus Schmidinger wrote:

> Henning Holtschneider wrote:
> > 
> > On Sat, 2 Jun 2001, Roland Praml wrote:
> > 
> > > > Does this happeen with _any_ recordings made with VDR 0.80pre7, or only
> > > > with specific channels and/or programmes?
> > >
> > > I don't know, sometimes it happens, sometimes not.
> > 
> > Same thing here, sometimes it works, sometimes it doesn't. It doesn't seem
> > to have anything to do with the recording or VDR's cutting mechanism.
> > 
> > Apart from that, the remuxed output file have remained useless for me so
> > far, because the audio/vide delay "drifts" throughout the file and mplex
> > only evaluates the a/v offset at the beginning of the file. So, in the
> > beginning, everything is fine but the delay increases towards the end of
> > the file.
> > 
> > I've been thinking about changing the behaviour of mplex so that it will
> > constantly monitor the a/v delay and insert silence or drop frames (like
> > PVAstrumento does under Windows) but my knowledge about MPEG streams is
> > very limited. If anyone already has a solution for this problem, I would
> > be glad to learn more about it ;-)
> 
> So would I, because I really would like to make VDR create 100% correct
> recordings, without the need to remux them afterwards...
> 
> I wonder how it can be that the a/v offset "drifts" throughout a recording.
> The original data that has been broadcast _must_ have been ok, because
> otherwise the live signal would have to show these drifts, too, wouldn't it?
> 
> Is the increase of delay you are observing always in the same direction, or is
> it random? 
> 
> Klaus
I think I evaluated that, the drift comes from the disk system being
so busy (lots of change in scene) that a block of data is late.
Then somehow the driver re-aligns data internally? perhaps.
If you keep the disk from other things, so no swapping occurs, this drift
does not happen.
(You can watch the harddisk light, if it is on all the time, you have a
problem), it shoul blink few times a second perhaps.
But I am only testing this now on a K6 2-450, so maybe systems with
less processor speed have a bottle neck somewhere else.
So I think it is not a VDR problem, as it also happens with cat > /dev/video
etc.
I can make the drift appear by forcing some extra harddisk traffic,
just copy couple a few of those av_pes files and run 'yes' a couple of times
perhaps, with nice -n -19.
Hehe

Regards
Jan


> -- 
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> 
> Klaus Schmidinger                       Phone: +49-8635-6989-10
> CadSoft Computer GmbH                   Fax:   +49-8635-6989-40
> Hofmark 2                               Email:   kls@cadsoft.de
> D-84568 Pleiskirchen, Germany           URL:     www.cadsoft.de
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