[linux-dvb] Re: Interesting DVB-T issues

["Edward Wildgoose" <ed@wildgooses.com>]

> > there are 2 problems currently:
> > 1) in DVB transmissions often there are huge preload times in the audio
> > stream
> > (such as audio_pts ~= video_pts - 5);  it's an old story, and mplayer
> > resyncs after few seconds;
>
> Well, BBC ONE and TWO now have zero preload time, and now VDR has no
preload
> time either.  Video and audio are instantly in sync on all channels.  I
> think the only change was the new channels.conf which has different HP, LP
> rates and PCR pids...
>
> Does that make sense?
>
> > 2) the pcr pid is totally ignored, so sync is made respect to audio (if
> > I remember correctly);
> > in mplayer-dev-eng of september there's a message by Arpi explaining
> > this behaviour

OK, using VDR: BBC ONE and TWO have PCR on the video channel, audio is
instantly in sync.  ITV 1/2 and Channel 4 have PCR on a seperate pid and
audio is out of sync until I add the PCR pid into channels.conf, then these
channels are instantly in sync on channel change.

So PCR seems to be very important for proper timesync.  Now looking through
remux.c in vdr I can't see anything clever happening with the PCR timecodes,
so is this something which happens in the driver?

Just to be clear, without the PCR pid set, then VDR is doing the same as
mplayer, but with PCR set then audio and video are instantly synchronised.
Does this make sense?

Ed W



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