[linux-dvb] Re: Audio sync

[Rene Bredlau <murray@blubber.de>]

Hi,

On Tue, Apr 08, 2003 at 03:54:21PM +0200, Klaus Schmidinger wrote:
> Ralph Metzler wrote:
> > 
> > Klaus Schmidinger writes:
> >  > Ralph Metzler wrote:
> >  > >
> >  > > Klaus Schmidinger writes:
> >  > > ...
> >  > >  > Are you saying VDR should set VPID, APID _and_ PCR-PID when recording?
> >  > >
> >  > > Yes.
> >  >
> >  > How does this correspond with your posting from 14:09:
> >  >
> >  >    During live viewing the ARM uses the PCR to set its own system clock
> >  >    (STC). The PTSs (DTSs are dropped AFAIK) of the streams are then used
> >  >    for synchronization.
> >  >    During playback only the PTSs are used. The STC is set according to
> >  >    the first PTS. It also is reset if there are large PTS gaps.
> >  >
> >  > This made me believe that the PCR-PID only needs to be set for _live_ tv viewing,
> >  > but not for _recording_.
> > 
> > OK, if you record separately (not the stuff you are viewing or via
> > time-shifting), you don't necessarily need to record it.
> > But again, newer hardware which pipes TS playback through its hardware
> > demuxer might need a PCR to work.
> 
> VDR doesn't replay TS, it stores its recordings as PES (as far as I understend these
> formats) and replays that.
Thats right. Vdr internaly remuxes the TS stream received by the device into a PES Stream with specific maximum stream length (defined by IPACKS inside remux.c). Per default all header information of the PES Stream are removed by this routine with one exception. If a PES stream is received (wraped inside a TS packet) which has a PTS header extension the header is copied.

This header fields are important for a/v sync if all header are rewritten audio and video get out of sync soon.

The conversation is happening during transfer mode, too. 

> 
> > Depending on how this hardware is driven (open/closed driver or
> > microcode/firmware) you might not be able to work around this and will have
> > to fix your files ...
> 
> But this would apply only if VDR would replay TS, right?
Alot of tools assume to get a PES Stream (AC3 patch for example or tools to burn recordings). So this is maybe not an option.

-- 
So long
	.\\urray


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