[mythtv-users] Ultimate Mythtv vid card, part II

[steve at nexusuk.org]

On Tue, 10 Feb 2004 papenfuss at juneau.me.vt.edu wrote:

> 	Directly into the VGA connector?  Is this a progressive TV or have you 
> cooked up a NTSC/PAL output for the vid card? 

Standard PAL interlaced TV.  I have a X modeline that has the PAL 
specification timings and a small circuit (consisting of a transistor and 
a bunch of resistors) to combine the H-sync and V-sync into a composite 
sync signal.  The raw RGB from the VGA port along with the composite 
signal from the circuit is then fed directly into the TV.  Since X is 
running in native PAL resolution and timings, the output from the VGA port 
is compatable with the RGB input of the TV.

The circuit is on my website:
http://www.nexusuk.org/projects/vga2scart/index.php

The modeline I use is:
"768x576pali" 14.76 768 789 858 944 576 580 583 625 -hsync -vsync interlace

> me when the vid card manufacturer/driver assumes, "It'll be different when it 
> flickers, so throw away every other line to make it look good for the 
> consumer."

The card manufacturers are probably worried about all the support calls 
they'd get from clueless lusers complaining that "my desktop flickers when 
I'm outputting it to my crappy TV" :)

> 	So this would be the deinterlace playback without having to have it on 
> all the time, right?  Is that an interpolation process right now?

Basically it'd deinterlace playback only when the frame is going to stay 
on the screen for longer than a single frame period (i.e. if you're 
running in slow-motion or paused).  If you pause a fully interlaced frame 
with lots of motion on it then it flickers horribly because the TV keeps 
drawingboth fields (which in high motion scenes can be very different).
AFAIK the default deinterlacing algorithm in Myth is a linear blend (i.e. 
take an odd line and the adjacent even line and average them together).

-- 

 - Steve                                             http://www.nexusuk.org/

     Servatis a periculum, servatis a maleficum - Whisper, Evanescence