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-   -   Image tearing/image artifacts during video playback (http://www.nvnews.net/vbulletin/showthread.php?t=130917)

mbobak 03-31-09 04:35 PM

Image tearing/image artifacts during video playback
 
Hi all,

I'm running Ubuntu 8.10, MythTV 0.21+vdpau patches, and NVidia driver 180.29.

When I play recorded content on MythTv (or in mplayer, for that matter), I get image "tearing". My guess is that the picture isn't syncing correctly? The condition was quite severe, until it was suggested I disable compositing. I did so, and the situation improved notably, but I do still see artifacts and tearing, particularly when there's a scene with fast motion.

Anyone have any thoughts/ideas as to what can be done to prevent or minimize this problem?

Thanks,

-Mark

cthulhu 03-31-09 05:13 PM

Re: Image tearing/image artifacts during video playback
 
I've experienced tearing with mplayer if I had mythtv running in the background. Killing mythtv eliminated the tearing. If the tearing also happens when you're only running mythtv, I'd suggest trying not to use OpenGL for mythtv, though this is just a guess/hunch.

Stephen Warren 03-31-09 05:51 PM

Re: Image tearing/image artifacts during video playback
 
Did the situation improve when you
a) Turned of a compositing manager, but kept the X composite extension enabled
b) Disable the X composite extension

From your description, it sounds like you did (a), but you need to do (b) to get tear-free video at present. This will be resolved soon.

If you did in fact do (b), please see the driver README for a description of cases where overlay v.s. blit is used. Something is still forcing you into the blit path, if you are still getting tearing.

mbobak 03-31-09 06:41 PM

Re: Image tearing/image artifacts during video playback
 
Stephen,

I think you nailed it in one try. I had disabled a compositing manager, but not the composite extension.

I did:
sudo nvidia-xconfig --no-composite

to disable the compositing extension. I've just done it, and started watching again, and so far, I see no artifacts or tearing.

On a related note, I found some info on ubuntuforums advocating setting OpenGL VSync to Blank and enabling the TripleBuffer option. I'm wondering if those options will help/hurt the situation?

Also, I look forward to the issue w/ compositing being resolved. It's only eye candy, for the most part, but it'd be nice to have compositing enabled and still have good quality video.

Thanks for your help!

-Mark

Stephen Warren 03-31-09 08:31 PM

Re: Image tearing/image artifacts during video playback
 
There are two issues when a compositing manager is enabled:

a) The compositing manager must sync its own rendering to VBlank. Most compositing managers render using OpenGL, so the OpenGL sync to VBlank setting will help here.

b) There's an issue in the damage events spec and interaction with GLX_EXT_texture_from_pixmap, such that it's not possible for the compositing manager to atomically pick up rendering to redirected windows. This could cause tearing too, and unfortunately it can't be worked around at present. This may/may-not affect you depending on all manner of system timing issues.

mbobak 04-01-09 05:41 AM

Re: Image tearing/image artifacts during video playback
 
Stephen,

Again, thanks for the help. It's been several hours since I totally disabled compositing, and no signs of tearing.


-Mark


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