[mythtv-users] M10K XvMC video stuttering

[Michael Carland]

Sorry to beat a seriously illin’ horse, and for the long post.

I was having this problem with .17, and waiting to see if it went away 
in .18, because I hadn’t been keeping up with patches.

I know turning off XvMC solves problems for many people, and that XvMC 
support is improving.

But I also thought that XvMC is working well for people with EPIA M10K 
setups.

I’m having a problem with stuttering video/sound on live tv playback. 
Playback from recorded content plays fine.

With both XvMC’s enabled (or just the VIA one), and deinterlace Bob (2x 
framerate), the picture looks great, but there are bursts of 
“prebuffering pause”s and “WriteAudio: buffer underrun” messages that 
go along with stuttering video.

With both XvMC’s disabled, no deinterlace, there are no pauses, no bad 
log messages, but there is video tearing.

With both XvMC’s disabled, and bob deinterlace, video is shown twice, 
split screen, with same picture squished on the top and the bottom, 
colors are funny (lots of purples and blues), and the whole screen 
flickers solid green. It’s a little noticable.

I’ve just built a new backend with a different MB/CPU, so I don’t think 
it is backend hardware related.

I’m using the following
Debian testing
X.org 6.8.2
Unichrome VIA driver from CVS, checked out 2005-03-15.
freedesktop.org DRM driver from CVS checked out 2005-02-10.
MythTV 0.17 (now .18)

I tried more recent checkouts of the VIA driver and DRM, but still had 
the same problem, along with some new ones, so I rolled back.

Other than the pause and underrun messages, there are no errors in the 
frontend log. The log does mention XV and VLD are being used:

2005-04-16 14:00:42.913 Using protocol version 15
2005-04-16 14:00:45.099 Opening audio device 'default'.
Using XvMC version: 1.0
XvMC found and using VLD surface
2005-04-16 14:00:45.131 Using XV port 64
2005-04-16 14:00:45.788 Using realtime priority.
2005-04-16 14:00:45.810 Changing from None to WatchingLiveTV
2005-04-16 14:00:45.816 Video timing method: DRM
2005-04-16 14:00:46.084 prebuffering pause

vmstat doesn't show anything odd, compared to when it is playing 
smoothly. No swapping at all. top shows no IO waiting, plenty of idle 
CPU (60-70%). There is about 3% hi and 3% si in top, which I can't find 
a description for, I don't know if that is a problem. The stuttering is 
very bad when I first go to live TV, or when I change channels, but 
then smoothes out after a minute or two. It never goes completey away, 
it can come back in bursts, but isn't nearly as noticeable after a 
while. If I pause so I'm 15 seconds behind, it doesn't seem to help, 
but if I pause about 1 minute or more, it seems to rarely pause once I 
start again.

I didn’t think the 3D parts of OpenGL were used, but I figured if I 
could get a good glxgears value, it might indicate I had the drivers 
set up properly. Before doing this, glxgears was around 50fps, and 
after going through the motions, it is now around 530fps, so I think I 
have OpenGL set up properly.

Playing prerecorded content works smoothly.

Two smaller problems, they are not a big deal, but if there are any 
ideas it would be nice to cross them off the list.

1) When watching video, overscan hides the VBI dots at the top, but 
they are visible in the program guide, and the preview of recordings. I 
know the crop filter doesn’t work with XvMC, but I gave it a try just 
in case XvMC wasn’t used in either of those two modes. crop=1:0:0:0 had 
no effect.

2) When entering and exiting the program guide, the video jumps down 
and left slightly between the time the guide is selected, and actually 
appears. Not a huge deal, but it is pretty noticable, since this causes 
the VBI to be visible.

Any suggestions?

Thanks,

-Michael