[mythtv-users] Good TV Out (long -sorry)

[Bruce Markey]

Chris Martin wrote:
>>This is what I call a 'straddle' event. If there is no retrace
>>timing for the card, the frame buffer is updated at equal frame
>>intervals unaware of when the actual retraces will occur. If the
>>update and retrace are at almost the exact same time, the update
>>could happen just before or just after the retrace deadline. This
>>causes rapid jitter until they go out of sync again (pause would
>>accomplish this). Ironically, the more accurate the timing, the
>>longer these events last.
> 
> 
>>Both OpenGL and DRM methods will get the retrace timing and can
>>avoid this problem.
> 
> That makes sense;

Really? It's awkward as hell to describe and I've failed miserably
in the past. I'll have to keep this for future cut'n'paste ;-).

>  so presuming the ati drivers have OpenGL support,
> how do I go ensuring that it is used?  Is it something that you have
> to tell Mythtv to use at complie time (and if so is it in Axel's

For 0.17 or earlier, you have to edit settings.pro and uncomment
the lines for opengl then recompile vsync.o . For current CVS and
0.18 you'll need to "./configure --enable-opengl-vsync [other args]"
and recompile.

> RPMs), is it something you have to enable in xorg.conf or is it
> something that has to be dealt with somewhere else?

Possibly. I don't use any ATI cards or drivers for MythTV anymore
but usually something needs to be included in the X config file
to load OpenGL support. See you driver's documentation.

When you start playback, the frontend logs the timing method that
it will use:

...
2005-04-12 12:30:04.469 Opening OSS audio device '/dev/dsp'.
2005-04-12 12:30:04.905 Using XV port 106
2005-04-12 12:30:05.864 Using realtime priority.
2005-04-12 12:30:05.996 Video timing method: SGI OpenGL
...

If you run "mythfrontend -v playback" it will print out more messages
about which methods it tested and why it decided it couldn't use them.

--  bjm