[mythtv-users] Bob deinterlacing drops frames, but not high CPU

Matt Doran matt.doran at papercut.biz
Sat May 19 00:21:26 UTC 2007

Doug Larrick wrote:
> Matt Doran wrote:
>> Is this error because my refresh rate is 20040usec , which is 49.9Hz ... 
>> which isn't double 25?    Isn't it being a bit picky?  :) 
> Actually, technically, the calculation is that 20040 usec * 2 = 40080
> usec, which is longer than 40000 so we can't display two frames (fields)
> per refresh.  You need to somehow convince your video card to really do
> 50 Hz.
> You might try raising "74.25" in your modeline by a little bit, say to
> "74.26" which *should* be 50.0067 Hz.
> Note that 74.25 MHz / 1980 total pixels / 750 total lines does indeed
> exactly equal 50.000 Hz, so something is fishy if you're actually seeing
> 20040 (which is 49.899 Hz)... you should run 'xvidtune -show' which will
> report what modeline you're actually using.
Hi Doug,

I finally got a chance to update my modeline.  I used xvidtune.  For 
some reason I need to set my rate to slighlty above 50Hz in the modeline 
to make it really 50Hz.  It seems to drop 0.1Hz for some reason??

Anyway, after doing that I can get bob running with opengl vsync and it 
works well (only 20-30% CPU).  Thanks a lot for your help!!

I also had a quick question about the deinterlacers.  Bob seems to give 
me smoother panning/scrolling ... but it results in a slightly shakey 
appearance on things like text and the OSD.    Why does bob result in 
this shakiness?

How is it that digital STBs can get smooth deinterlacing without 
jerkiness or the shaky text?   Are there better deinterlacing algorithms 
that could be used that aren't implemented in Myth for whatever reason?


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