[mythtv] XvMC studdering

Dave Just justifiably at cwazy.co.uk
Wed Jan 18 17:17:00 UTC 2006

> I have XvMC working very smoothly on a celeron 450 with 192mb of  
> ram.  This is with an agp nvidia 5200.  The setting that makes the  
> biggest difference is to turn on chromakey osd.  This frees up an  
> additional buffer on the card for video decoding that was  
> previously used for osd.  There is not yet a setting in the setup  
> page for mythfrontend, however the setting can be enabled with an  
> entry in the database.  Search the -dev list to find the setting as  
> I can't remember what it is exactly.  Also, I have found that  
> OpenGL vsync actually causes more stuttering and adds extra  
> processor load.   I run with OpenGL vsync off.

Thanks for the chroma key suggestion: I hadn't tried this and it's  
nice to see a colour OSD with XvMC.  On the other hand, the  
appearance and movement of the OSD still cause audio stuttering and  
video jitter.  On some streams this happens continually whether or  
not the OSD is shown. Worse, with the XvmcUsesTextures setting I get  
garbled OSD display for *non*-XvMC output.

I wonder if it could be some aspect of my hardware: I have an onboard  
GeForce 4 MX which shares the system RAM (this is *not* an MX 440 as  
I mistakenly said before).

  - Dave

NB: For chromakey you need in xorg.conf in the device section for the  
NVidia driver the flag:

   Option "XvmcUsesTextures" "false" # use 3d engine for overlays

And an entry in the database (don't think this is available from the  
mythtv setup):

   insert into settings values ('UseChromaKeyOSD','1','mymyth.mynet');

See ticket #512 on trac.

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