[mythtv-users] Experiences with XvMC

Scott catfather at donpoo.net
Sun Jul 31 16:55:51 EDT 2005

On Jul 31, 2005, at 3:06 PM, Todd Ignasiak wrote:
> 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
> playback

I don't have a tuner in my MythTV box right now. For my setup with  
the SD DirecTIVO it doesn't make sense for me to invest in a MythTV  
box for SD. My Pundit strictly handles DVD playback using MythTV as a  
nice front end to Xine.

> 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

I have a few test clips I used. One of which was the test clip found  
on the pchdtv.com site. Others are available from various locations  
on the Internet. On the Pundit with a 2.4GHz Northwood P4 chip I  
cannot playback any HDTV streams without serious stuttering. All to  
be expected. Once I popped in the PCI FX 5200 I was able to play back  
the same test clips with the previously noted issues. CPU was around  
35% during playback.

> 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.

I've thought about this too. Right now the investment is to high for  
me to pick one up on the cheap to try out. As such, I think the way  
to go would be a nice powerful CPU and a quality DVI based video  
card. Together with existing Linux post processing software in Xine  
(which uses stuff based on tvtime) I think the quality would be as  
good as it gets for a HTPC.

> 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.

I think lots of us would. Right now such a solution doesn't exist. i  
would expect as HDTV becomes more popular here in the US we'll see  
something for Linux in the next 5 years. Right now hardware HDTV  
decoding and playback on Linux seems to be where V4L was 5-6 years ago.

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