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

[Gert van der Knokke]

Nick Craig-Wood wrote:

>On Sun, Apr 11, 2004 at 12:40:41PM +0200, Gert van der Knokke wrote:
>  
>
>>Nick Craig-Wood wrote:
>>    
>>
>>>Or alternatively why doesn't mythtv display interlaced video the way
>>>it was intended to be displayed?
>>>
>>>Mythtv is currently displaying frames at 25 (PAL), 30 (NTSC) Hz which
>>>look like this
>>>      
>>>
>>Yep, but your monitor isn't... Since most monitors  run at 70-100 Hz you 
>>never get this right and you'll end up having the tearing effect during 
>>motion...
>>    
>>
>
>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? :-) (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..

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...)

>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.

>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 :-)

Gert