[mythtv-users] xorg.conf Section Extension

R. G. Newbury newbury at mandamus.org
Tue May 6 19:26:08 UTC 2008


Drew Tomlinson wrote:
> I'm attempting to enable XvMC on a Nvidia FX 5500 card.  I've followed 
> the instructions on the wiki 
> (http://mythtv.org/wiki/index.php/XvMC#NVIDIA_2).  My question is 
> regarding adding these lines to my xorg.conf file:
> 
> Section "Extensions"
>     Option "Composite" "Disabled"
> EndSection
> 
> What do these lines mean?  "Section Extensions" is not in the xorg.conf 
> man page.  Googling reveals lots of advice to *enable* it for Compiz but 
> no explanation of what it does.

Actually it IS in the xorg.conf man, but buried in the section on 'Load 
Modules'.
Since by default (on nvidia and intel) all of the extension modules are 
loaded, this section allows you to turn off modules which are not wanted.


> My experience is that when this section is in my xorg.conf, chromakey 
> works.  With chromakey working, I don't get nearly as much audio stutter 
> when the OSD is on.  Also, the picture looks like it has been 
> deinterlaced.  However the Off | Half | Full | Stretch view modes do not 
> work properly.  Left and right cropping is OK but vertical cropping is 
> only cropped from the top.  The bottom is not cropped.  This feature is 
> important to me because I have a widescreen television and use the Full 
> mode when viewing letterboxed content.  I hate watching a small picture 
> in the middle of my screen.  ;)
> 
> When this section is not in my xorg.conf file, chromakey doesn't work as 
> evidenced by this snippet of my frontend log:
> 
> 2008-05-06 11:15:18.338 VideoOutputXv: XvMC Adaptor Name: 'NV17 Video 
> Texture'
> 2008-05-06 11:15:18.388 VideoOutputXv: Ack! Disabling ChromaKey OSD
>                         We can't use ChromaKey OSD if chromakeying is 
> not supported!
> 
> Thus the audio is very choppy anytime the OSD is displayed.  However the 
> Off | Half | Full | Stretch view mode work just fine.
> 
> Is there anyway I can have both chromakey and proper cropping?  I've 
> included my xorg.conf for the nvidia 169.12 drivers below.

It does not appear so. I have no idea why Stretch does not work, even 
when you are using Chromakey. You might try playing with all of the 
settings in Playback Profiles, noting that Bob is the only filter which 
works with XvMC. I presume you are using IA444 (or whatever that one is) 
when you are not using Chromakey. There is another one...Softkey??

Try setting up a different profile which does not use XvMC (or change 
the priorities of those listed, so that you can try a different filter.)

As to the choppy audio, if you go into Setup-> TV Settings -> Playback, 
there are 2 settings on the first page of that section..extra audio 
buffering (which is often useful) and use video as timebase. The latter 
seems to cause problems on my Intel-video box and I have not tested it 
on this nvidia based box. But the extra audio buffer is almost a 
necessity with a lower-powered machine, sucj as my old Via motherboard.

Also, setting the OSD to NOT FADE seems to help generally. Personally, I 
don't much care whether the OSD is in grey or colour. So as long as the 
video + audio is fine, then I don't care about the actual load-lowering 
effects of Chromakey. (Chromakey is a further off-loading of work-load 
from the CPU to the GPU, beyond what XvMC is handling.)

  Thanks,

You are welcome. Glad to see that the wiki page is being used (and that 
  vindicates me for the time I spent re-writing it)


Geoff


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