[mythtv-users] Live HD TV jumpy

[DaveD]

My setup, for the most part is working quite well.  I have a pcHD3000, a
DVICO Gold, and a PVR-500.  This gives me two HD and two analog (I
haven't used the analog portions of either HD card for "sound" reasons,
NPI).   The recording and playback is working quite well.  I can watch a
full 1020i or 720p HD recording while all 4 tuners are recording!  I
find this amazing, but with the tuners doing all the work, recording is
just dumping onto the disk.  HD playback is another story; CPU usage
runs pretty high (about 90%, mostly Xorg, then Mythfrontend), no matter
what the tuners are doing.  Still, it all works well.  Until I try to
watch live HD TV.  Live standard def works fine, but HD is jumpy and
blocky.  Badly so.  So bad that Myth gives up, some times, and says "an
error was encountered while displaying video" then dumps me back to the
menu.  I don't really understand this.  Isn't live TV just like watching
a recording while another show is being recorded?  It just happens to be
the same show.

I'm running MythTV 0.21 from an Atrpms RPM (0.21-155_trunk_r13045) on an
updated Fedora 5, x86_64 system.  I had the same problem with 0.18, 0.19
and 0.20.   Hardware is an Athlon 64 3200+ with 2gB of RAM, one 300Gb
SATA and one 500Gb SATA.  Video is an Nvidia GeForce FX 5200 dual head
(single GPU) with the analog (15-pin) driving a Mitsubishi 37-inch LCD
HD TV/display (actually a 1920x1080 native monitor with separate tuner)
and DVI driving a 1280x1024 17-inch monitor.  Audio is ALSA:spdif
pass-through on a Creative SB Audigy.  I am using XFS filesystem on top
of an LVM, shared between my two disks.  I used to run ext3 on a
dedicated disk and had the same problem.  Signal strength is always good
(> 90%) as it's being fed by a 4-way amplifier connected to cable (clear
QAM-256).

I'm guessing the problem has something to do with sound, but I'm not
sure why.  Just a feeling/guess.  I had to turn on "Extra audio
buffering" and "Aggressive Sound card Buffereing" to get HD playback
smooth.  I'm not sure why this is, either, if it's digital pass-through,
but I guess it's gotta sync up some time.

Deinterlace settings don't seem to make any difference.  That makes
sense, since it's digital HD:  the signal already has all the fields.
(Deinterlace settings don't make any difference on standard def analog,
either, but that's another problem that I don't really care about, as
I'm spoiled with HD!).

I have tried every setting I could find (and MythTV has LOTS of them)
and nothing helps.  Any suggestions and/or explanation of how watching
live TV is different from watching and recording different shows at the
same time would be greatly appreciated.