[mythtvnz] GeForce xfx 6200 & WinTV-NOVA-TD 500?

[Steve Hodge]

On Sun, Jun 13, 2010 at 4:57 PM, Nick Rout <nick.rout at gmail.com> wrote:

>
> On Sun, Jun 13, 2010 at 2:13 PM, mythtv <mythicalbeast at slingshot.co.nz>
> wrote:
> > But I did not think PCI or AGPx8 had the bandwidth for true HD1080
> > playback..
>
> Come on, PCI is 133 MB/s, the highest rate video you are likely to
> find is a bluray at 48 Mb/s, that's plenty of room for overhead!
>

Yup. I don't know where this perception that encoded video is bandwidth
intensive has come from but it seems to be pretty widespread despite being
dead wrong. As you say PCI has about 20x the bandwidth required. Harddrives
also have at least 10x the required throughput. Encoded video is trivial for
every part of the system except sometimes the CPU.

That's obviously feeding the encoded video straight to the card, you
> are possibly correct if you are trying to decode on the cpu and
> transfer the raw stream to a video card over PCI, I haven't done the
> math.
>

1080p is about 2 megapixels per frame x 4 bytes = 8MB per frame. PCI could
only manage about 16 frames per second. So yes, PCI can't do raw 1080p60.
But AGP 8x is 2133MB/s and could quite happily handle five 1080p60 streams
at once. If you can get the pixels to the bus then AGP 8x is more than
capable of pushing them to the video card.


> Remember these cards probably use an API that myth and other media
> players do not (yet) know how to play with.


This is the key question in my mind. Does the card have X drivers? If not
then can it's video buffer be accessed directly? Because if it can't then
you couldn't do the gui or the OSD via that card. It looks like a similar
situation to the old PVR350 output - an option that is no longer supported
in myth and always had significant limitations relative to using a normal
video card (some people were willing to live with those limitations for the
superior interlaced output but with vdpau that advantage seems to be gone).
I really doubt there will be any interest from the devs in this sort of
thing so someone else will need to step up.

Cheers,
Steve
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