[mythtv-users] Mac OS X choppy playback at high display resolutions, such as 1080p

[MythTV]

On Oct 9, 2007, at 7:52 PM, Eric Robinson wrote:

>> What I think is happening is that in order to keep the line count a
>> multiple of 16 the video height is being set to 1088 but the actual
>> content is 1080.  When this happens the pixel aspect ratio difference
>> becomes 0.013 which causes a transform matrix to be created so
>> Quicktime will try to "transform" the image to maintain the aspect
>> ratio.  By allowing a 0.015 difference in pixel aspect ratio to be
>> ignored it should remove the need for the transform.
>
> Would that have an effect on a screen that's been translated or zoomed
> in on?  I found that changing the setting mentioned before ONLY works
> if you *haven't* changed any of the settings in the Overscan Settings
> menu.
>
> The video through one of my tuners comes through with garbage to the
> left and bottom on NBC in HD.  I tried shifting the image with the
> Playback overscan options to compensate.  The picture looked good but
> the jerkiness came back again.  I then put the screen-translating
> options back to 0 and set an overscan percentage of 1 for both
> horizontal and vertical.  This also got rid of the garbage but brought
> back the jerky picture.
>
> Would the proposed patch address these little gotchas, too?
>
> Awesome work, by the way.
>
Eric,

I did some quick testing.  It looks like that anytime that the image  
needs to be transformed (offset or scaled) it causes a problem so the  
patch wouldn't solve the problem if you set an overscan or offset.

I don't know of an easy solution that will allow overscan or offset  
without using the QuickTime transform function which seems to be  
causing the problem.

The most likely solution would probably be to move to a CoreVideo/ 
OpenGL based VideoOutput class that could utilize the GPU for the  
transformation.

Mino