[mythtv-users] XvMC Prebuffering Pauses

[Brian Foddy]

I know this is probably one of the most beaten issues, but
I'd like some input.

My machine  is able to play 1080i content from
CBS/NBC without too much difficulty.  There are occasionally
streams of pauses, especially with fast  forwarding but they
don't cause too much problem and its easy to just jump back
15 seconds and it picks up fine.  Once its running, playback
is fine without pauses.

The problem has always been ABC (720p).  A program like the
Lost will play for about 5-10 seconds fine, then stream prebuffering
pauses, hanging the playback with really no way to ever get
it playing correctly.  Fox is also the same way.

Which is why its strange.  I've been browsing the code, putting
some variable dumps, etc.  In Ringbuffer.cpp, the 1080i is
a higher estimated bitrate (>18000) and uses a larger block size,
the 720p is about 13000, and standard tv is about 10000.
Also, when played on a faster frontend that is able to play
smoothly, the 720p content regularly takes less CPU load than
1080i.  So why is 720p such a problem?

I've also tried changing NvAGP from 0, to 1, to 3, no change.

What resource is actually short when 
Prebuffering pauses occur?  Originally I thought it was the 
XvMC internal buffers that weren't getting released fast enough.
But then I wondered why most often occurs starting up and fast forward
so I began to wonder if the player is starved of frames from the
disks?  Playing the content from local drives doesn't seem to help tho either.

System details:
Frontend:
P3-1400, 768MB ram, Nvidia 5600 or 5700 Ultra video (I've tried both).
FE NFS mounts video filesystem via 1Gb network, nfs mount options:
rsize=8192,wsize=8192,hard,intr,nfsvers=3,actimeo=0,tcp
Linux 2.6.16.23 kernel, 1000Hz CONFIG_HZ (I've tried lower also),
all preemption options.

Backend
Dual Xeon 2400 P4, 2GB ram, 5 raid0 160MB scsi disk drives, 1Gb network
to frontend.

I've also tried this from a dual P3-1000 machine, and even tho it can't
quite play any HD content smoothly, it doesn't ever get the streams like
the 1400 does.

I'm looking for guidance here, even if its making personal tweaks to 
the source.  But so far nothing is making any difference at all.

Thought?
Brian