[mythtv] DVD playback issues, patch

David Engel david at istwok.net
Wed Nov 25 02:57:25 UTC 2009

On Tue, Nov 24, 2009 at 06:36:21PM -0700, John P Poet wrote:
> ...and that happens even when doing this with "simple" 720p mpeg2.  My
> system should be able to decode 100 frames per second pretty easily.
> So, the video being +3 frames behind the audio does not make sense.
> There is no excuse for my system no being able to "keep up", unless it
> is not being allowed to.  I assume the problem is that there can only
> be one-frame-per-refresh, and the refresh is 60Hz.  I don't know what
> the solution is, but I would love it if Davin or Mark could come up
> with it ;-)

I haven't followed any of this thread until this message.  Please
pardon the interruption if I'm way off base.

John, I believe you've touched on the reason I have my HD-PVR attached
STBs set to 1080i instead of 720p -- interlaced content stretches much
more smoothly than progressive.  With the fallback deinerlacing
options limited to 1x, you never have more deinterlaced frames than
refresh intervals (60, in my case) so you never have to drop any
frames.  With progressive content, you always have more frames than
refresh intervals so you always have to drop frames and the result is

I have an idea that might remedy this.  We detect when we have more
video frames than refresh intervals similarly to how we detect when to
use the fallback deinterlacers.  When we detect this condition, what
if we discard every other video frame?  In a sense, we fallback to a
"0.5x deinterlacer."  Since we discard frames at a regular rate
instead of somewhat randomly as currently done, the result might be as
smooth current the stretching of interlaced content.

David Engel
david at istwok.net

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