[mythtv-users] DVB cards and encoding

Christian Hack christianh at pdd.edmi.com.au
Tue Dec 9 05:32:38 EST 2003


> > I've been looking at Myth TV for a while and I'm trying to 
> > decide what 
> > hardware to buy.  I would like to buy an EPIA M10000 
> > motherboard and I 
> > know that they aren't very powerful for encoding.  I am therefore 
> > thinking about getting a PVR250 or PVR350 card to put in it 
> > to do MPEG 
> > encoding.
> > 
> > I have also been looking at DVB cards, specifically the 
> > Nova-T and I was 
> > wondering if the output from this card (into the computer) is 
> > MPEG(2?) 
> > and if so does that mean that recording from this card 
> > requires little 
> > CPU power or does the data from this card need encoding in some way?
> 
> It doesn't need encoding as such. It needs "processing" though. DVB
> streams can have more than one audio and video stream 
> embedded in them.
> So the software needs to strip out the unwanted streams. Since it's
> essentially throwing data away, it takes very little CPU. I think some
> cards can even do this themselves. Can they? I might have 
> made this last
> bit up.
> 
> On my XP2400+ nForce 1 board I can't really see it even use the CPU.
> Maybe a few percent every now and again.
> 

I'm going to reply to my own post because I probably wasn't all that
clear and the other poster may have just confused you.

DVB streams consist of multiple MPEG2 streams so require no encoding
whatsoever, just the stripping of unwanted streams. As I said - very
little CPU. Decoding is another story.

To decode a SD (Standard Definition) stream on my XP2400+ completely in
software takes about 15-20% of my XP2400+. A HD stream is up around the
60-70% mark if I can get it to work. 

_Some_ of the DVB cards also have hardware DEcoders. As far as I am
aware these are not supported very well in Linux (if at all). They
definitely aren't supported in MythTV. MythTV does support the CLE266
and XvMC accelerations if available though. I haven't tried either of
those.

CH



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