[mythtv] Idea for interlaced playback.

Bjørn Konestabo bjornko at math.uio.no
Fri Nov 11 18:28:30 EST 2005


Daniel Kristjansson wrote:.

>It does not sacrifice spatial resolution of the video when shown
>on a monitor that can handle doubling the framerate. If used with
>a television set, the driver throws out half your frames, so you
>end up with half the vertical resolution.
>  
>
No, half my frames are not thrown out even though I use a tv-set. What
happens is that each field is shown at 50Hz (I'm in europe) blown up across
the framebuffer. Each field is refreshed by the tv-screen, but because
 
  1) myth can't tell when my tv is doing odd or even refreshes, data may be
     refreshed at the wrong place,  
  2) the rescaling of the field blends things a bit (possibly the center 
pixel
     is somewhere between the refreshing rasterline?), i do get the full
     framerate, but not the full spatial resolution. It not exactly half 
either,
     but it's noticably worse than it needs to be.

I've heard the bobdeint-filter works differently in xvmc than it does in 
xv.
Unfortunately, I've never gotten xvmc to work.

>You can do this with interlaced monitors, such as televisions sets, by
>simply setting things up properly. Use the same resolution in lines as
>the monitor, use OpenGL vsync, and don't enable deinterlacing.
>
If I do that then the fields will be refreshed out-of-order half the time
I start a clip, or after a while if playback drops a frame. This is 
exactly the
problem my wannabe-filter is supposed to fix.

>This is known as an interlaced framebuffer, not "bob and weave".
>
Sorry for being sloppy with the terminology. If what I have described is
indeed an interlaced framebuffer, then this is what I want. Simply 
pumping the
frames out interlaced as they are does not work for me.



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