[mythtv] Need help diagnosing slow XvMC problem

Jerry Rubinow jerrymr at gmail.com
Sat Jan 14 21:45:47 UTC 2006

> -----Original Message-----
> From: mythtv-dev-bounces at mythtv.org [mailto:mythtv-dev-bounces at mythtv.org]
> On Behalf Of Jerry Rubinow
> Sent: Tuesday, January 10, 2006 5:10 PM
> To: mythtv-dev at mythtv.org
> Subject: [mythtv] Need help diagnosing slow XvMC problem
> When I play back content using XvMC, it plays back slower than real
> time, both HD and SD, cpu is not maxed out.  I haven't been able to
> figure out why, but it seems like it might be a Myth problem (but
> maybe not?).
> Here's what I have:
> Separate front end/back end.  Front end is a 2.8Ghz P4 with a GeForce 5200
> PCI.
> Running FC4 setup per Jarod's guide.
> Myth SVN as of about a week ago.
> Nvidia driver version 7667.
> Here's what I've tried:
> Tried with and without OpenGL sync.
> Tried Various Nvidia drivers up the the current 81xx.
> Tried playing same video files over nfs using mplayer with xvmc and
> they have no problem, so that seems to eliminate disk, network, or
> graphics card bandwidth problems.
> No deinterlacing going on.
> When it plays inside myth, everything is slow-mo.  Not a stuttering
> problem.  CPU usage is down below 20%.  If I turn off XvMC, SD plays
> back fine, but HD maxes out the CPU.  However, I hadn't been
> optimizing for P4 (d'oh), so that can probably be improved somewhat.
> But if I could get the XvMC thing working that would be a much better
> solution, since I'd have room to spare for deinterlacing and whatnot.
> All suggestions welcome.  I'll post whatever logs would be most
> helpful to diagnose this, just let me know which ones.
> -Jerry

On 1/14/06, Rob R <rob.r at plutohome.com> wrote:
> What does the console output/frontend log show while it's playing in slow
> mo?
> I get that exact behavior when "extra audio buffering" is disabled.   My log
> shows a ton of "prebuffering pauses".  With extra audio buffering enabled,
> it works correctly *most* of the time but I haven't been able to totally
> solve it.

Good suggestion.  I tried that and the problem got somewhat better,
but the video is still a little slow and sound is choppy.  When I do
mplayer -vo xvmc -vc ffmpeg12mc on the same mpeg file, it play back
absolutely perfectly, video and sound.

My current playback settings are
-no deinterlacing
-standard xvmc decoder
-enable opengl vsync for timing
-enable realtime priority threads
-extra audio buffering (problem is worse without this)

Myth svn, version 0.19.20051208-1

Enclosed is the frontend output from -v all,nodatabase.  Things that
look like they might be prolems to my untrained eye (but maybe they're

-VideoOutputXv Error: Couldn't get the color key color
-lots and lots of "Broadcasting free space avail" messages
-nVideoVideoSync: VBlank ioctl did not work, unimplemented in driver?
-DRMVideoSync: Could not open device /dev/dri/card0, No such file or directory
-a bunch of NVP: Video is X.XXXXX frames ahead of audio, skipping A/V wait.
-a bunch of audio waiting for buffer to fill: have 2048 want 4096
-a bunch of NVP: prebuffering pause

CPU is around 40%

Any suggestions on what to concentrate on and what not to worry about?


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