[linux-dvb] Re: hdtv scanning

Wolfgang Wegner wolfgang at leila.ping.de
Mon Nov 6 15:25:05 CET 2006


On Mon, Nov 06, 2006 at 03:10:48PM +0100, Marco Masotti wrote:
> > ==========================
> > Date: Mon, 6 Nov 2006 13:53:27 +0100
> > From: wolfgang at leila.ping.de (Wolfgang Wegner)
> > To: Benny Amorsen <benny+usenet at amorsen.dk>
> > Cc: linux-dvb at linuxtv.org
> > Subject: Re: [linux-dvb] Re: hdtv scanning
> > ==========================
> >
> >[...]
> > As long as PCs do not have any means to synchronize frame and 
> > audio rate,
> > they are not really suited for MPEG decoding IMHO.
> > 
> >
> 
> I don't question that but, then,  how big do you consider the time skew to have audio and video tolerably in sync? I was assuming that receiving dvb-s programs, in-software decompressed by a processor in a shared memory proposition, was deemed common now. Also, it would seem that the whole sense of this list would be substantially lessen if only intelligent card (those capable of doing 100% hardware assisted processing - not counting which areas of code functionalities would be included in such assistance ) were supposed to correctly work.

My main goal was to say why I do think that special hardware still has
its place although actual PC hardware can perform the task of decoding
even HDTV yet.
Lip-sync is not the real problem, as long as sound is not earlier than video
some few milliseconds do not matter. However, when it comes to HDTV, I would
prefer to get the quality that is possible with both audio and video and
not some interpolated signal (in either time or space) - and that is what
you have to do when using standard PC hardware.
We can see that this is possible, and results are quite good with current
software decoders, but it is not as good as with a dedicated decoder chip
which generates its clock from MPEG SC, like every set-top-box does. We
(DVB) are broadcast, and not decoder-driven...

*dreaming* a graphics card giving the possibility of adjusting the master
clock from the TSC and having on-board audio capability, also synchronized
from the same clock, would be perfect IMO.

Regards,
Wolfgang




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