[mythtv-users] Possible XvMC prebuffering issues solution?

Jason Ferrara jason at discordia.org
Fri Dec 1 16:55:20 UTC 2006


I'm convinced that there is some sort of timing bug in the playback  
code.

With mythtv 0.19, I had HD playback with XvMC working perfectly on  
three different frontends:

Dual 3.06Ghz Xeon / GeForce FX 5200
2.8Ghz P4 / GeForce MX 440
2.0Ghz P4 / GeForce MX 420

I upgraded to mythtv 0.20, leaving everything else (os, kernel,  
nvidia drivers, settings) the same, and then got stuttering with  
"NVP: prebuffering pause" and "WriteAudio: buffer underrun" messages  
on all three front ends. XvMC is still working. I see the grey OSD,  
and CPU usages for the three frontends are 30%, 45%, and 75%, so its  
clearly not a lack of processing power issue. I was able to get rid  
of the stuttering on the dual xeon by checking "Extra audio  
buffering" and "Enable OpenGL vertical sync for timing". Doing the  
same thing on the other two front ends changes the way the stuttering  
sounds, but doesn't get rid of it.

Based on this and all the other possible solutions I've seen posted  
on this list, it seems to me there is a timing related bug in  
playback. If you're lucky you can manage to change settings to jiggle  
the timing such that the bug doesn't affect you, but basically HD  
playback is kind of broken.

- J


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