[mythtv] Idea for interlaced playback.

Daniel Kristjansson danielk at cuymedia.net
Fri Nov 11 18:39:18 EST 2005

On Sat, 2005-11-12 at 00:28 +0100, Bjørn Konestabo wrote:
> 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
In anycase bob-deint is the worst filter to use with an interlaced
monitor, because it doubles the framerate. If some hardware deals
with this less well than others, then so it is.
> I've heard the bobdeint-filter works differently in xvmc than it does in 
> xv. Unfortunately, I've never gotten xvmc to work.
Only the implementation is different, the final output should be about the same.

> >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.
Ah, you are using an analog frame grabber ?

> >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.
So basically you need to flip the fields, so that the odd lines are
are on the odd lines, and even lines are on the even lines?

You should be able to use the same code we use for bob-deint to detect
if you need to swap the lines odd and even lines. This should be fairly
easy to do, just look at frame->top_field_first. See calc_bob() in
VideoOutputXv for an example.

When you have a patch ready, assign the ticket to me.
I'd like to improve the video output a bit in 0.20...

-- Daniel

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