[mythtv-users] XvMC Prebuffering Pauses

[Brian Foddy]

On Monday 24 July 2006 05:58 pm, Steven Adeff wrote:
> On 7/23/06, Brian Foddy <bfoddy at visi.com> wrote:
> > 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
>
> I had a similar issue a while back, updating the nvidia drivers to one
> of the recommended two and running .19-fixes ended up getting me
> going, though i had other issues with XvMC so I don't use it. Will
> this work for you? dunno, XvMC is very very finicky.

What .19 fixes are you referring to?  I'm using stock .19 and
8762 Nvidia drivers.  Going back to older Nvidia versions is a real
hastel because of having to drop back kernels, causing driver cascade,
etc.

I'd also like a good answer to a question myself and Gary Dezern (and
probably others) have pondered.  What is really short, free buffers to
display to the card, or frames not ready to be displayed.  From the fact
that skipping around, FF, etc can cause moderate PBPs, I'd guess it
may be a lack of frames to be displayed.  

From my digging around so far, it looks like the software is maybe 
not using big enough buffers for the content.  When its given full
1080i content, it opens up large enough buffers to handle it.  But these
are just a little smaller and its using smaller blocks and buffers.  Perhaps
too small...

Brian