[mythtv] [mythtv-commits] mythtv commit: r11013 - in trunk/mythtv by nigel

Andrew Kimpton awk at awkward.org
Sat Sep 2 18:19:49 UTC 2006

Nigel Pearson wrote:
>> I've seen some commentary elsewhere on the 'net that Apples YUV420 ->
>> YUV422 (and I guess by association the YUV420 -> RGB) conversion is
>> poor. Experience here seems to indicate that it's more than poor.
>> So why do we even have an option to invoke it ?
> 	I think we were hoping that Apple would eventually
> provide hardware-assistance in QuickTime. But yes,
> we could remove the option with little impact.
I get the distinct impression that all of the future effort by Apple in 
this space is in CoreVideo and providing mechanisms to link QuickTime to 
CoreVideo - ie.

MPEG (YUV420) -> YUV422 -> CoreVideo -> Screen

CoreVideo takes care of the YUV422 -> RGB conversions on the graphics 
card - basically by using hardware 'shaders' to convert YUV to RGB. I 
don't think we'll see any more effort being made by apple to improve YUV 
conversions in QuickTime - rather they'll just continue to enhance the 
conversions done by CoreVideo. Right now CoreVideo only supports YUV422 
(and RGB), but it's possible they would add YUV420 in the future.

MPlayer has a CoreVideo rendering option and on my PowerBook G4 it 
seemed to save approx. 5-6 % points of CPU usage over the software 
YUV->RGB conversions that MPlayer also has.

It seems like implementing a videoout_corevideo module in Myth would be 
a good thing - indeed that's something I'm just starting on now.
>> Given that there are now Altivec and MMX routines
> 	G3?
> 	I haven't tested on an old iMac or PowerBook
> in a while, but I think QuickTime did it faster.
Yep - legacy support is a problem, CoreVideo for example is only 
supported on 10.4 and 10.3 with QuickTime 7.x - it's also not supported 
on every Macintosh even with the right software versions. Particularly 
lesser performing PowerPC macintoshes (PPC Mac Mini and some iBooks) do 
not support CoreVideo. It is however supported on all current Intel 
Macintosh's including the Intel MacBook and Intel Mini.

Probably the best solution is to take this out of the hands of a user 
setting and detect the platform/capabilities and then choose the 
appropriate videoout module and appropriate YUV conversions.

Andrew 8-)

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