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Old 08-01-06, 11:36 PM   #8
mythtv_buster
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Join Date: Aug 2006
Location: Northern CA
Posts: 6
Default Re: What card for 1080P60 with XvMC

Quote:
Originally Posted by pe1chl
I'm getting a little bit closer...
The nvidia card shares its interrupt with the diskdrive the HD movie is being read from
....
But apparently it is no problem when using xv or gl output. Only with xvmc. And only with HD. (SD from the same disk is no problem)
Why?
When using XvMC with nvidia, the video card assists with decoding but does not do full decoding. This means that data transfers to/from the video card multiple times when using XvMC whereas without it the CPU decodes it fully and sends only the final data to the video card. Multiple trips to the video card means higher bus utilization/bandwidth.

All else being equal, a 1080i HD stream uses about 7x more bandwidth than a 640x480i (which would be a pretty hires NTSC encoding) stream. Then take into consideration that this increased bandwidth from HD vs SD is a double whammy as it applies to taking the data off the hard drive as well as going to (and from, and to, etc. in the case of XvMC) the video card.

More bus bandwidth usage also translates to more interrupts. Make sense now?

It sounds like the motherboard is wired so that what ever you put in that PCI slot will share an interrupt with your video card. If you have an open PCI slot move the IDE controller to it. If you don't then try swapping it with a device that doesn't use much bandwidth (won't generate a lot of interrupts.) It looks like you already know that "cat /proc/interrupts" is your friend in determining which hardware generates a lot of interrupts.
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