[mythtv] timestretch: predictive frame skipping (was Re: DVDplayback issues, patch)

Mark Spieth mark at digivation.com.au
Wed Nov 25 23:18:19 UTC 2009

>No worries. I guess a good place to start from would be: how would it 
>affect playback? (If you think having avsync_adjustment not be a multiple 
>of the refresh rate would affect playback in some way, it would maybe help 
>me understand your argument)

Im coming at this from a control systems point of view.
you have a model which should accurately represent the underlying system.
the model is necessary since the variables themselves are hidden.

my understanding is that each call to wait for frame is aligning with the 
next displayed frame at the refresh period.
(or 1/2 frame/field in the case of x2)

it makes no sense to wait for a partial frame and then wait for the next 
otherwise you would wait for the sub frame and then wait for the rest of the 
displayed frame.

thus effectively nothing happened. thus avsync_adjustment for that pass has 
no effect and would have to accumulate until it was larger than 1 display 
period. I suppose this would work too. I prefer controlling the quantized 
adjustments in the controller in question.
however there is always more than 1 way to skin cats. the effect would 
probably end up being the same.
though the interaction would be more complex and quite possible dependent on 
the implementation in waitforframe. so that would be a good argument for not 
relying on fractional waitforframe adjustments.


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