[mythtv] G400-TV questions

Erik Arendse mythtv-dev@snowman.net
Wed, 04 Dec 2002 16:56:05 +0100

At 4-12-02 16:27, "Michael Kedl" <kedlm@knology.net> wrote:
>I'm just jumping in here with my limited understanding :-)
THNX for the long answer...

 > sounds reasonable; you just have to find a setup for your video card
>that does "Real TV Output Sync (TM)".
G400-TV should Do-Exactly-That (TM) :-)

The problem according to this maillist is that the hardware MJPEG 
compressor is used for decompression as well. But its one at the time, and 
when recording the hardware support for scaling and YUV->RGB conversion is 
not available.

>I think the problem is that "Real TV Output" is pretty ugly.
>You need to generate sync timings that lead to hidden areas around all 4
>edges of your "data area".
G400-TV is one the few Hhigh quality TV-out cards with overscan support.
What I want is MythTV to be VCR-compatible.
As far as I know the G400 grabs the overscan area, and when displaying 
overscans the same way. At least with separate recording/playback. When 
doing it simultanously it should be possible I think to use software 
YUV->RGB (already present in MythTV source) and skip the scaling. That way 
you don't have to use the xv interface to Xfree4.

With all these questions I try to find out if I am not making any mistakes 
before investing ni a used G400, a lot of other people on the list made it 
clear it won'w work out of the box with the current mythtv.

 > In fact, for some settop boxes I helped create, we display VGA data on TVs
>in overscan mode and I adjusted the "desktop" size to look "great" but
>with a visible resolution of say 580x400 in NTSC mode (approximate, its been
>years and I don't have the exact numbers handy).  This was a closed system
>and worked great, but how many people have that kind of mode/desktop size
>available under windblows/linux/etc.?
My mythTV will be a closed system, its only output running PAL 576x480 (or 
whatever, don't have numbers handy either, but visible PAL standard and 
equal to G400 HQ-grabbing resolution)) at 50 Hz interlaced. G400 should 
handle overscanning, mythtv will be used with its downscaled output feature 
to have it fully visible in the overscanned output on TV.

>I know I'm rambling, but the answer is "yes, what you propose would lead
>to the best quality image with least artifacts, etc" but you will
>probably have to tweak the video timings on your video chip to get it
>to look right since the drivers for winblows/linux are most likely setup
>to make the other 99.1% of the world happy and display data underscanned.
Tweaking should be handled by the G-400 I hope, and yes "best quality image 
with least artifacts", anyway given the terrible cable-input, is my only 
Holy Grail.

> > Another question: Why the YUV<-->RGB problems, can't I just grab the
> > configuration in the format I need for putting it on the output device?
Was signalled as problem on the list earlier, not sure why, MythTV already 
has yuv2rgb on board.

>Basically there are different formats for capturing video and displaying
>video.  I believe YUV typically is used for TV because of the nature
>of encoded TV signals.  It leads to smaller data captures that is basically
>still "right".  RGB is usually used for computer desktops because it
>gives exactly the same video color depth to each pixel and each color
>in a pixel (this is not at all what TV does).
Yep. G400-TV is grabbing hardware MJPEG in YUV422P if I understood 
correctly. Always thought all MPEG variants were strictly RGB, but have to 
read up the docs a little I guess.

>Hope some of that helps :-)
It did...
Still looking for more G400 related info however :-)