[mythtv-users] CPU Performance required three dumb capture cards (WORKING!)

Adam Felson a.f.5 at pobox.com
Sat Mar 27 10:27:35 EST 2004


> From: "Gregorio Gervasio, Jr." <gtgj at pacbell.net>
> 
>         What's the usage like with 480x480?  I think your system
> should be able to handle that.  I have two Bt878 cards on an
> Athlon XP 2500+ (1.83GHz), nForce2 system capturing 480x480 MPEG4,
> 2000 bitrate (1500 eff.), 4MV and HQ disabled, adjust and quickdnr
> filters enabled.  CPU usage is 60-75% when recording two programs and
> playing one more at the same time.  I don't transcode

Thanks for the heads-up. I went back to doing mpeg-4 on the fly with no
transcoding and I set the resolution to 480x480.  It was the transcoding
that was choking the system and causing it to crash;  sometime's I'd see
5-6 transcode processes and perhaps they had used up all the physical
memory and caused the system to thrash.  

Right now I have two capture cards doing RT mpeg-4 @ 480x480.  With two
cards recording and tvout playing a stream, I get 20% idle on the athlon
2400.  And the system doesn't crash any more!   (at least it made it
through the night for the first time in a week)  Another thing I did was
quit using a low latency pre-emptive kernel.  I'm now running
linux-2.4.25 straight from kernel.org without any of mandrake's
finaglry.

I much prefer dumb capture cards over smart ones.  They're half the
cost, mpeg-4 compression ROCKS (<1gb/hr vs. 4gb/hr for mpeg2), and
there's no need to transcode everything.

When I get the third capture card I want to decidate it to TV only use
and use rtjpeg compression.  If the system can't keep up, getting an
athlon XP 3000 is cheap enough.

Last question:  how do I dedicate a capture card for tv viewing only?
I have a few programs on the guide set to record anytime they're
anywhere and it's possible for three programs to be available at the
same time;  in such a situation, I want the conflict logic to treat it
like I just have two cards.



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