[mythtv-users] Sandy Bridge Graphics w/MythTV

[Michael T. Dean]

On 07/22/2011 11:58 AM, jzigpublic wrote:
> I came across the following solution for Sandy Bridge Video Tearing in 
> MythTV.  The quote was pulled from this site:
> https://bugs.freedesktop.org/show_bug.cgi?id=37686
> It worked for me with an i3 CPU and an Intel motherboard with Intel 
> HD2000 on-board graphics.  No more tearing.  I'm using MythBuntu 11.04.
>
>> In order to play 1080i video content on my system running mythbuntu-11.04, I
>> created a new playback profile modeled after the "High Quality" playback
>> profile.  The new profile differs in that it uses xshm for the video renderer
>> (as opposed to xv-blit).  Please note that xshm says that it cannot scale video
>> in case this a problem for your setup


FWIW, Xshm is a terrible renderer to use for video.  It's extremely 
inefficient and, as mentioned, has issues such as lack of scaling, etc.

Xv, which is likely what you were using when you noticed the tearing, 
should automatically prevent tearing, though some video drivers do 
require flipping a switch--probably labeled something like, "Work 
properly," or "Do the right thing," or, "Sync to vblank" (OK, really, 
not like the first two, but...) in some configuration program.  But, it 
is possible that the drivers for the new Sandy Bridge graphics are 
broken and don't properly handle sync for Xvideo.

See http://www.gossamer-threads.com/lists/mythtv/commits/451677#451677

That said, Xv is a 20+ year old API that shouldn't be the focus of 
modern hardware/drivers.  Instead, you may want to try the OpenGL 
renderer (which is a much more modern approach to video--rather than 
Xshm, which is a step back even from Xv).  Again, you may need to set 
some driver-specific video-syncing switch to prevent tearing (and your 
drivers may have a different switch for Xv and OpenGL video).

With the OpenGL renderer, you'll also get additional benefits, such as a 
full-resolution (rather than video-resolution) OSD (meaning the OSD 
won't be squished to fit in a 4:3 video you're playing back with 
letterboxing on your widescreen display, and OSD fonts will look pretty 
even on standard definition video played back on your high-definition 
display).  The Sandy Bridge graphics should have sufficiently-powerful 
OpenGL capabilities to allow use of the OpenGL video renderer.

Mike