[mythtv-users] pcHDTV - 2 questions

[Doug Larrick]

On 11/06/03 01:35:16, Jarod C. Wilson wrote:
> For starters, the GF4MX won't output any interlaced modelines, so  
> 1920x1080i is out. My set doesn't do 720p, so that was out for me.  
> Next step down is a 540p modeline, which is basically electronically  
> equivalent to 1080i, if you do 1920x540p. However, I couldn't ever  
> get that rez to take, so I backed off to 960x540p, and it works just  
> fine. Everything gets scaled down a bit and you lose some definition,  
> but the picture still beats the pants off S-Video and/or NTSC. From  
> what I understand, 960x540p seems to be the norm for folks using GF4- 
> class video cards w/HDTV, though you may have to tweak the sync pulse  
> for your set. I'm pretty confident you'd be able to come up with a  
> modeline that worked, derived from either mine or Ian Forde's.

What he said.  I'll add that I *was* able to get 1920x540 to work on my  
set -- just double the dotclock and all the horizontal paramaters.   
Myth is not happy -- it's not scaling H and V separately for the video  
out -- but I hope to work on fixing that.

I also found that, for jitter-free playback, it's important to enforce  
that your modeline produces a vertical refresh of 59.94 Hz, matching  
the source material.  The sets seem to lock on to a narrow range of  
horizontal refresh for each mode -- 33.75 kHz for 1080i/540p, 45 kHz  
for 720p (though this one doesn't work for me, could be wrong), and I  
dunno for 480i or 480p.  So between those two, your vertical timings  
are just about sewn up, since 33.75k/59.94 = 563 total lines.  You can  
of course play with the # of active lines and sync pulse.  You have a  
little more flexibility in the horizontal timings, and it took a fair  
amount of experimentation for me to find timings with about the same  
amount of overscan as the vertical.  The dot clock is then once again  
determined for you, 33.75 kHz * your total horizontal size.

Note also that xvidtune is pretty useless if you want to hold your H  
and V refresh rates constant, as it's unwilling (unable?) to adjust the  
dot clock on the fly.

Here's what I use:

Modeline  "540p" 39.956   960 1020 1100 1184    540  550  551 563   
+hsync +vsync # 39.956 MHz 33.75 kHz 59.94 Hz
Modeline "540pw" 79.912  1920 2040 2200 2368    540  550  551 563   
+hsync +vsync # 79.912 MHz 33.75 kHz 59.94 Hz

-Doug
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