[linux-dvb] Re: Clock synchronization

[<mocm@metzlerbros.de>]

Toby Jaffey writes:
 > 
 > On Sat, Mar 02, 2002 at 11:01:26AM +0100, Ralph Metzler wrote:
 > > Toby Jaffey writes:
 > >  > Do the available DVB cards have voltage controlled 27mhz oscillators for
 > >  > this function or is it managed some other way?
 > 
 > > That's all controlled by the firmware on the card.
 > > The driver just selects the PID.
 > 
 > In the cards with a hardware decoder that makes sense. The decoder would
 > run at the speed dictated by the 27mhz VCXO. But, in the cheaper cards
 > which only do a demux then rely on software decoding, how does the
 > software decoder adjust it's speed accordingly? Is PCR recovery done by
 > the software decoder?
 > 
 > Is it just forced to repeat/skip frames to make up for the time
 > difference?
 > 
 > Or does the provided software decoder take a clock pulse from the DVB
 > card's VCXO to run by?

What provided software decoder?
There are a couple of MPEG2 decoders for Linux, which have different
synching schemes. Most don't handle transport streams yet and you have
to use some TS to PS/PES converter. And they don't necessarily need an
external clock from the DVB card or even an SCR/PCR to get synching
right. Even the DVB hardware doesn't need SCR/PCR information for
that. 

Marcus



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