[mythtv-users] XvMC on NVidia with Myth .20 (Anyonegetting goodHD off a P4 3

Brad Fuller bradallenfuller at yahoo.com
Mon Jan 8 20:30:31 UTC 2007

Drew Bernat wrote:
>> Whoa... XVMC is explicitly a video card driver thingy. It has NOTHING to 
>> do with the tuners. XVMC makes use of the video card *hardware* to do 
>> stuff which would otherwise be done by the main CPU is producing the 
>> video output. Which is why you see discussions of the computer power 
>> needed to decode HD. You need either a pile of computer grunt, OR an 
>> Nvidia or VIa video chipset which supports XVMC.
> Right. However:
> HD-resolution show recorded via HD tuner card: XvMC works
> SD-resolution show recorded via HD tuner card: unknown
> SD-resolution show recorded via SD tuner card: XvMC doesn't work
> This leads me to believe there is something about the _recording 
> format_ off the card that causes XvMC assistance to break, and not the 
> inherent resolution of the program. That's what I mean by tuner 
> difference - that's basically the only varying component right now.

XvMC, AFAIK, is a mechanism to offload IDCT and motion compensation 
chores to the GPU. Right?
Thus, by definition mpeg2 streams from OTA HD are going to be different 
than mpeg2 streams from your PVR card that does the mpeg2 encoding.  So, 
the decoding of a stream from OTA HD and from you PVR card are going to 
be different.

What do you mean "XvMC doesn't work"? What leads you to this conclusion


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