[mythtv-users] Experiences with XvMC

Todd Ignasiak ignasiak at gmail.com
Sun Jul 31 15:06:50 EDT 2005

Hi Scott,

I've been doingh the same analysis on HD playback .   I've been doing
XvMC with an FX5200 AGP card.  When it's working well, it's very good.
 But, I get the "prebuffering pause" issues, which causes choppy

I'm surprised that you were able to do HD playback via the PCI bus.  I
didn't think the bandwidth was sufficient for 1280x720x24bits at 60+fps. 
  Maybe XvMC changes the equation a bit..  Can you still get decent HD
playback without XvMC?

Another thing I'm interested in is the 'Unichrome' display adapters. 
This S3/VIA video chips do full MPEG decoding, not just the iDCT+MC
done with XvMC.  I don't know if it is any more/less capable with
things like de-interlacing.   Also, the 'Unichrome' version is
integrated into the motherboard, I don't know if they have the same
capabilities in their add-in cards.   Prior to moving to MythTV, I
used a 'MyHD' card in Windows.  It had a hardware MPEG decoder, which
did a nice job of scaling and de-interlacing, which almost no CPU
requirements.   I would love to find something similar for MythTV.

On 7/31/05, Scott <catfather at donpoo.net> wrote:
> Having been on the list for some time I was familiar with nvidia +
> xvmc combination and wanted to try it out. I picked up an evga
> GeForce FX 5200 PCI adapter and stuck it into my SIS based P4
> Northwood 2.4GHz Pundit system. (Note: not the Pundit-R) Setup was
> done under Gentoo 2005.0 using all stable packages with kernel 2.6.12-
> r4. I wanted to put down some notes for others who might be
> considering the same.
> My goal was to evaluate the xvmc + nvidia playback quality for future
> HDTV use. For playback I used xine-lib 1.1.0 and xine-ui 0.99.4 along
> with a few 1920x1080i and 1280x720p clips. I also used some standard
> DVD video to compare xv with xvmc processing. My viewing was focused
> around deinterlacing and artifacts that might be seen from post
> processing. For a display I used DVI out at 1280 x 720 to my
> Panasonic PT-L500U projector.
> Setup of nvidia + xvmc on Gentoo is well documented and went off
> without a hitch using nvidia-kernel 1.0.7667. Over all I was
> impressed with the results. Using xvmc I was able to easily playback
> 1080i clips with about 35% cpu use. Considering the low end PCI bus
> on the Pundit system board and the low end GPU on the FX 5200.
> I had two issues that for me are critical.
> When using xvmc with Xine none of the OSD overlays would work. This
> meant no on screen information, subtitles, or closed captions during
> playback. I didn't investigate this to much however I think it could
> be worked around. One possibility seems to be with the Xine xxmc
> support.
> XvMC appears to do very simple one-field deinterlacing in hardware.
> Xine 1.1.0 has experimental XvMC bob deinterlace support which I
> enabled and saw some improvements. I compared various DVD (480i
> content) scenes played via Xv with Xine deinterlace post processing
> and XvMC with hardware deinterlace. It was pretty clear to me that Xv
> with deinterlace post processing was producing a much better picture
> than XvMC using hardware deinterlacing.
> Based on my testing I think using nvidia + xvmc could be acceptable
> when dealing with HDTV streams but should be avoided for standard
> NTSC 480i content or where ever else it isn't absolutely needed. The
> best solution, from an image quality standpoint, would be to avoid
> XvMC and use a powerful system to handle the HDTV content decoding
> and playback. Obviously that solution brings with a host of other
> problems dealing with heat and noise.
> Right now I'm unsure of which direction I'll go in. I know I will be
> scraping my pundit and setting up a full FE/BE in a nice HTPC case
> like the ones Silverstone makes. The cheap solution, for me, is to
> get a socket 478 ATX board that supports my existing P4, memory, and
> other hardware then add in a quality Nvidia AGP based adapter.
> Considering the prices of nice looking HTPC cases and silent power
> supplies this might be the way to go as an interim step.
> --
> Scott <catfather at donpoo.net>
> AIM: BlueCame1
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