[mythtv-users] TV out for unlisted card?

Rod Smith mythtv at rodsbooks.com
Tue Apr 3 18:24:57 UTC 2007


On Monday 02 April 2007 21:54, Angus wrote:
> Rod Smith wrote:
> > I assume this means you're intending to use some other video source --
> > Internet downloads, DVDs, or whatever. Such sources might or might not
> > use the MPEG-2 encoding for which XvMC support can be useful
>
>     Correct on the Internet downloads. I also imagined viewing streaming
> sources, but that's starting to look like an unsupported feature.
>     There's something I don't understand about XvMC though. Why is any
> is any coprocessing necessary for TV out anyway? From what I remember
> about slow CPUs 800MHz is plenty of smarts to decode your typical MPEG.

A "typical" MPEG? Although I suppose you could do a statistical analysis to 
figure out what's "typical," the CPU power required to play back an MPEG-2 
file will vary greatly with a number of factors, such as the resolution and 
frame rate. That's why it takes so much more CPU power to play back HD video 
than SD video -- there are simply more bits to twiddle when playing back HD 
video, but the computer must do it in the same amount of time. Typical MythTV 
SD recording resolutions are between 480x480 and 720x480 (in NTSC countries), 
although it's possible to go lower than that at the cost of reduced quality. 
If your source recordings are at lower resolutions than this, then you might 
well be able to play them back using substantially less than your 800MHz 
CPU's full power, but they won't look as good as higher-resolution 
recordings, all other things being equal.

> If it can keep up with a monitor why would it need any more for a TV out?

AFAIK, monitor vs. TV has little or no effect on required CPU power, assuming 
output from the same video card. (I suppose there might be a slight effect of 
refresh rate, but I'm not even positive of that.)

-- 
Rod Smith
http://www.rodsbooks.com


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