[mythtv] Idea for interlaced playback.

[Daniel Kristjansson]

On Thu, 2005-11-10 at 22:05 +0100, bjornko wrote:
> Sorry for comming on a bit strong, being newly subscribed to this list and
> all, but I've search through the mailing list archives (user and dev)
> looking for ways to get proper interlaced playback with correct field
> order to no avail.
> 
> The best I can get is either using the bob deinterlacing field, which does
> preserve temporal resolution but seems to sacrifice spatial resolution.
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.

> Three things are needed for proper interlaced playback:
> 1) You need perfect line matching between the video framebuffer and
>     the tv-raster-lines. This can (at least on my nvidia card) be solved
> 2) You need to synch at the field frequency.
>     With xv or the OpenGL synch function, this is no problem.
> 3) You need to update half the lines (one field) at one refresh, and the
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. With
progressive scan display devices you can achieve something very similar
using bobdeint.

> Some people seem to think you need to know when the TV-out is doing a
> odd-line or even-line refresh, which is not easy at all. But this is
> incorrect, all you need to do is make sure odd-field lines are only in 
> odd lines in the framebuffer and the same for the even fields and update 
> the fields in order. (This is known as "bob and weave")
This is known as an interlaced framebuffer, not "bob and weave". I
believe what you mean by "bob and weave" is called bobdeint in myth,
and is for progressive scan monitors, when used with interlaced 
monitors that can't work at double the rate you will halve your
vertical resolution if you use this.

-- Daniel