[mythtv-users] mpeg2 video stuttering

[ojw at weilerfamily.com]

After having ditched the idea that a 1.8Ghz P4 can display
1080i content, I invested in a dual core Wolfdale processor
(45nm) at 2.53Ghz and paired it with a Gigabyte GA-73PVM-2SH
motherboard (Nvidia 630i based mobo with a GeForce 7100 built
in).  I'm using two Pinnacle PCTV HD Pro USB capture devices
and am only tuning ATSC based terrestrial transmissions.  Both
mythfrontend and mythbackend are running on the same box.

The problem I'm having is that when I try to view either a
recorded show or something live'ish (from the ringbuffer),
the view jitters.  What should be obviously smooth scene
pans turns into jerky stutter steps through the scene.

I was thinking it might be the marginally supported PCTV
HD Pro USB stick but I found that when I transfer the
recorded MPEG file to a PC running windows XP (using
windows media player), the video playback is as smooth
as silk.  I checked the CPU utilization during playback
on my mythtv box using top and found that it's usage doesn't
go over 50%.  I also tried configuring for XvMC which results
in a good cpu usage drop (down to 30%) but the image still
stutters about the same amount.

I also tried playing the resulting mpegs in mplayer on the
mythtv box.  At first, mplayer told me I didn't have enough
CPU power to play the file so I used the -ao null option to
negate sound.  After I did that, mplayer didn't complain but
it stuttered more than during playback in mythtv.

I'm not sure where to go from here and was hoping you all
could direct me to further diagnostic efforts.  I'd be
happy to post whatever config information you think would
help diagnose this.  I'll start with the basics:

Kernel: v2.6.26.3
MythTV: 0.21.20080304-1
NVIDIA: 173.14.12
Using HDMI out at 1920x1080

Oliver