[mythtv-users] mythfrontend playback problems, but mplayer works

[Kevin Chmilar]

I have been using mythtv for a couple of years now and have built,
re-built, swapped hardware around and always managed to get everything
working perfectly, mostly by searching through this list.

I have recently set up a new machine and have one problem with video
playback.  The stream I am playing back was recorded from a PVR-250,
mpeg-2, NTSC, 480x480 resolution, default bitrate.

When I play the stream with mythfrontend, it stutters about every 20
seconds.  It seems to skip about half a second of video and audio.  If I
rewind 5 seconds, the skipped section plays fine.  I have tried turning
on the extra audio buffering and the video stream sync options (on the
first screen of the playback settings) and the problem persists.
mythfrontend puts out a "prebuffering pause" message when this happens.

If I use mplayer with the "-vo xv -vf scale" options to play the .nuv
file, then it plays flawlessly.  However, if I don't use those options,
I get the same stutter, and a message from mplayer saying something like
"Your system is not fast enough to play this file" along with
suggestions on options to try.

With both mplayer and mythfrontend, CPU usage is about 20-25%, with X
being 8-10%, and mythfrontend or mplayer at 10-12%.

I have also run xvtest, and it reports about 1100 frames/sec, which I
think should be adequate (my other system, with nvidia on-board
chaintech 7nif2 reports 6500 frames/sec).

Is mythfrontend not doing basically the equivalent of "-vo xv -vf scale"
that mplayer does?

Relevant system information:
Pundit-r
Gentoo, w/vanilla kernel 2.6.9, myth 0.16 built from source (no emerge)
xorg 6.8.0-r1
Using s-video out (NTSC), with ATI drivers (w/binary patch applied)
512 MB memory, 512 MB swap
Celeron 2.4 GHz CPU
PVR-250, ivtv 0.2.0-rc1c
200GB drive, dma is on, hdparm reports 62MB/s
xfs file system
mtrr enabled
apic enabled

After looking through the list, the things I haven't tried are
re-niceing the mythfrontend process, and using a 2.4 kernel.  I don't
think re-niceing will help, because CPU is not too busy.  I don't think
the kernel 2.4 option is feasible with this fairly new hardware.

I do notice that graphics and ivtv are sharing an interrupt.  Could this
be the problem?  I guess I could test this by unloading ivtv.

Any suggestions or comments are welcome.

cheers,
kevin