[mythtv-users] PVR-250 and MPEG2 question

Jarod Wilson jcw at wilsonet.com
Tue Sep 21 16:38:43 EDT 2004

On Tuesday 21 September 2004 12:20, Gert van der Knokke wrote:
> Jarod Wilson wrote:
> >On Tuesday 21 September 2004 10:44, Michael J. Lynch wrote:
> >>Any idea how much P3 CPU crank is needed to view 720x480 8Mb/s MPEG2
> >>video?
> >
> >My Athlon 800 with a GeForce 4 MX had no problems handling that exact
> > MPEG2 spec.
> >
> >>Is MPEG2 decoding
> >>significantly more processor intesive than MPEG4 decoding?
> >
> >MPEG2 decoding is less processor-intensive than MPEG4. Less decompression
> > to do. MPEG2 is also at least somewhat standardized, while there are
> > umpteen different MPEG4 variants...
> Maybe this is true but my experience is that because the PVR cards are
> recording in quite a high resolution, a slower P3 (read < 600 MHz) might
> choke. I found out for example that a Celeron 400 could handle live TV
> and recordings from a bttv card fine and played most AVI files without
> problems too but stuttered terribly on playing the files recorded by the
> backend after upgrading it to a PVR250 instead of the bttv.

Now that I think about it, I think I may have things bass-ackwards on that 
(sort of). I believe MPEG4 takes more horsepower to encode the same video 
stream as MPEG2 would, but you can achieve the same visual quality (in 
theory) at a much lower bitrate. On the decode side, while the viewing 
machine has to use a more complex algorithm to decode, it is generally going 
to be decompressing less than a third as many bits for the same visual 
quality. So the less bits for more complex algorithm tradeoff probably 
results in less cpu usage.

> It could be that to decode the MPEG2 stuff the extra instructions of the
> newer Celerons and P3's are (automatically) used.

Yes, the SSE instruction set helps out a lot.

> So I would advise not using a P3 under 600 MHz.

Definitely not.

Jarod C. Wilson, RHCE
jcw at wilsonet.com

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