[mythtv-users] Interlacing [was: Pvr250 issues - any suggestions?]

[Nick Craig-Wood]

On Mon, Apr 19, 2004 at 01:34:45PM +0200, Gert van der Knokke wrote:
> Nick Craig-Wood wrote:
> >Well there is always the vertical blank interrupt!  That worked fine
> >for avoiding tearing back in the bad old days (eg Atari ST!) for
> >games...
> >
> True, but which on which vertical blank is the interrupt generated ? The 
> TV out or the VGA vblank? :-)

A good point!  I was thinking of monitor output really as with TVout
one really should be able to do it properly...

> (With the Atari.. hmm, good old days.. it was easy as you had only
> one output.. but then some PAL games couldn't run on NTSC systems
> because there was less CPU time between Vblanks... ) Since the
> images from a PC VGA/TV-out are not in sync (due to the conversion
> from VGA to TV-out) it's gonna be difficult..

Yes including TVout is difficult!

> I must say that the TV-output of the Asus Pundit with the Winischofer 
> drivers has no visible tearing even though my monitor output 
> (simultaneous) runs at 75 Hz (which could explain it as this is 1.5 
> times the Vsync of my little Sharp PAL LCD beamer...)

The TVout that I've played with has not showed any problems either...
Some of the TVout circuitry is suprisingly clever!

> >You'll have to display some input frames for longer than others to
> >make the 25/30 fps, interlaced to 50/60 fps into the 70-100 fps
> >output, but from my own experiments at changing the frame rate of
> >video I know this isn't very noticeable.
> >
> You'll get jerky motion if you display some frames longer than the 
> others, especially with fast video which was made to move perfectly in 
> sync with the standard PAL/NTSC vertical blank.

Yes, but in my experience this isn't terribly noticeable...

> >I find this whole interlacing business very annoying!  Interlace was a
> >technical trick from the start of television to reduce the bandwidth
> >requirements - we really don't need it any more!
> 
> Yeah legacy sucks :-)

Indeed!


-- 
Nick Craig-Wood
ncw1 at axis.demon.co.uk