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

steve at nexusuk.org steve at nexusuk.org
Mon Feb 9 16:31:15 EST 2004

On Mon, 9 Feb 2004 papenfuss at juneau.me.vt.edu wrote:

> - I've got a couple of questions for the NVidia tvout folks.  Primarily, I'm
> wondering if you can truly get 480 lines of bone-fide output through some
> combination of drivers and/or nvtv?  When I got my GF2 MX400 awhile back, I

>From when I was using the TV out on an nVidia card, ISTR that the TV 
output hardware does some deinterlacing which reduces the quality of the 
output.  Basically that's good for showing computer generated stuff (i.e. 
the menus on Myth) since it reduces flicker, but not so good for the 
actual telly.

The nVidia cards also won't let you set the native PAL resolution of 
768x576 (at least with the closed source drivers), so you have so run in 
800x600 and let it scale the picture slightly (so you capture at 768x576, 
scale up to 800x600 and then scale down to 768x576 again, whcih is rather 
silly and can't do the quality much good).

> well as out.  Now, I'm pretty sure I shot myself in the foot.  First off, the
> second head won't do over 1024x768 or something ridiculously low, and secondly,

ISTR the second head on dual-head cards is actually driven off the bit of 
the chipset that was designed to drive the LCD screens in laptops, so it's 
really not designed to do nice resolutions.

> - Here's a good one...if there's a card that supports both XVideo and 
> Sync-on-green, wouldn't it be possible to write a dummy XVideo colorspace 

If you google around a bit then I'm sure you'll find some circuits that 
will inject the sync signals into the green signal (you should be able to 
do it with a couple of transistors)... if you feel competent with a 
soldering iron that is...

> "transformation" to go YUV->VUY?  The thought here is to do component out 
> without needing an external transcoder box.  Put the 'Y' on green with 
> composite sync, then put the 'U' and 'V' on red/green... just a VGA-BNC cable 
> and the TV's a VGA monitor.

Sounds like a nice idea, but isn't the YUV->RGB conversion matrix 
hard-wired into the hardware? (not sure on this one)..  if it is then 
you'd have to do the conversion in software, which would suck.


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

     Servatis a periculum, servatis a maleficum - Whisper, Evanescence

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