[mythtv] Jitter with time stretch

[Peter Bennett]

On 07/14/2018 09:52 PM, David Engel wrote:
> Did you try this with 1080i?  720p worked fine for me.  With 1080i,
> however, playback doesn't actually speed up for speeds greater than
> 1x.  It stays at 1x even though MythTV reports it being faster.  It
> dows slow down for speeds less than 1x, though.  Strange.
I did some timing on NULL audio and I discovered that with 1080i 
content, the method VideoOutputOpenGL::ProcessFrame takes from 13 - 15 
milliseconds. Also sometimes VideoOutputOpenGL::PrepareFrame takes 5 
milliseconds. At 60 fps, one frame needs to be displayed every 16.6 
milliseconds, so OpenGL the way we are using it cannot display more than 
60 fps of 1920x1080 images. At 60fps it is running at maximum speed. 
Without audio there is nothing that will drop frames to force it to 
catch up. The time stretch works with software decoding and NULL audio, 
presumably because that is rendered at 30 fps not 60.

Peter