[mythtv-users] Where's the playback bottleneck?

[Jerry Rubinow]

If I playback an HD resolution file, I get stuttering, pick a codec, any codec.

If I play it back with mplayer (-vo xv -vc ffmpeg12), also stuttering.
 If I play it back with mplayer (-vo xvmc -vc ffmpeg12mc), plays back
pretty much ok.

In all cases, myth and mplayer, CPU is between 20% and 50% (this is on
a combined front/backend, P4 2.8 Pundit, with onboard VGA disabled,
using a PCI FX5200).

The fact that I can playback the file in mplayer with xvmc, tells me
it's not a disk issue, and the fact that mplayer cannot play it back
smoothly with xv tells me it's probably not a myth issue.

Is it a bandwidth problem in the video card or the bus?  Some BIOS
setting incorrect?  Does anyone have any suggestions for how to narrow
it down and tell for sure where the problem might be?

Is anyone using an original (sis-based) Pundit for HD playback successfully?

Thanks.

-Jerry