[linux-dvb] Re: hdtv scanning

Wolfgang Wegner wolfgang at leila.ping.de
Mon Nov 6 17:15:23 CET 2006


On Mon, Nov 06, 2006 at 03:59:46PM +0000, Torgeir Veimo wrote:
> On Mon, 2006-11-06 at 16:45 +0100, Wolfgang Wegner wrote:
> > The more difficult part is to synchronize the playback part (audio
> > sample
> > clock and video clock (frame rate)) to this new system clock - this is
> > simply
> > not possible with any of the PC hardware I currently know about.
> > (Except
> > the FF DVB cards, which do it internally.) 
> 
> What about the scenario where you're either using a budget dvb-t card
> with playback using a FF dvb-s card, or have two FF card, but playing
> back the stream from the other card? What clock does the FF card then
> sync to?

to be honest: I don't know, because I only used the FF card with VDR,
but used only budget cards for my own programming.

In case the FF card gets a (partial) transport stream, it could still
synchronize to the contained PCR packets - depending on interrupt and
transport latency (DMA?), the jitter will be higher than with direct
processing, though. If there are no PCR packets in the stream, it can
only use a free-running clock adjusted by guessing from PTS. But still,
you will have audio and video in sync without lost/double frames...
(as long as the intermediate stream has PTS)

Regards,
Wolfgang




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