[mythtv-users] Sandy Bridge Graphics w/MythTV

Michael T. Dean mtdean at thirdcontact.com
Fri Jul 22 22:50:04 UTC 2011


On 07/22/2011 06:44 PM, jzigpublic wrote:
> On 7/22/2011 11:54 AM, Michael T. Dean wrote:
>> 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.
>>
>> Seehttp://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.
>>
> Unfortunately, My Sandy Bridge and  OpenGL stutters on MythTV 
> recordings, so I guess there isn't enough horsepower there.  And 
> you're right Xshm has it's problems too.

Yeah, I know I could only do 1x playback using OpenGL with my old GF7200 
and GF7800 cards.  My GT220 can do as much timestretch as I want with 
it.  I assumed that the Sandy Bridge GPU should be able to do 1x without 
problems.  If not, your best bet is to get Intel/whoever's working on 
the Intel video drivers to fix sync-to-vblank for Xv.

Mike


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