[mythtv] bugfix patch for XvMC deinterlacing

[Doug Larrick]

Brandon Beattie wrote:
> Just curious,
> 
>  After a week of testing this patch is working very well.  It has been
> some time since I have tried XvMC and am very impressed with how wel it
> is working now.  
> 
>  I have noticed 2 problems with my myth box if XvMC is enabled.  The
> first is that at the end of watching a show, or hitting escape
> (basically anytime you quit watching) mythfrontend segfaults. 

This probably belongs on the -users list, but...

How up-to-date with CVS are you?  That sounds a little like the OpenGL 
context bug that got fixed as part of my vsync rewrite.  Do you have 
vsync.c (old) or vsync.cpp (new)?  You're gonna have to provide a stack 
trace if you want more than just guesses, though.

>  The second problem is that the frontend will hang with "waiting for
> video buffer" and sometimes "prebuffering pause" errors when I hit fast
> forward too quickly, or just at some odd moments.  I was trying to get
> to the end of one show and setting bookmarks.  I saved one then tried
> fast forwarding, which it did then froze after a couple seconds.  Upon
> going back to watch again, myth froze with the errors when it started
> playback at the saved possition.

I have assumed this is related to ff/rew occupying more video frame 
buffers than it actually needs.  XvMC doesn't have as many available as 
straight Xv.  If we run out of free video frames the MPEG decoder (such 
as it is with XvMC) has nowhere to write new frames, so we can make no 
forward progress.  If you manage to get back to normal playback speed it 
all resolves itself.

Of course, there's also the hang that everybody sees if you press Pause 
while in ff/rew.

-Doug
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