[mythtv-users] Driving Australian TVs

[Hamish Moffatt]

On Sat, Jan 01, 2005 at 10:42:53PM +1100, William Uther wrote:
>   I've been building a MythTV box.  I have a VisionPlus digital DVB-T 
> capture card (giving me a PAL, MPEG2, 16:9, 50Hz, interlaced video 
> stream).  I'm trying to find the best way to get a picture on my TV (a 
> 4:3 aspect ratio, 100 Mhz Grundig with vga, scart, svideo and composite 
> interfaces).  I'd like to be able to watch the 16:9 signal both 
> letterboxed (see the whole thing with top and bottom black stripes) and 
> zoomed (just grab the middle 4:3 section out of the 16:9 signal - lose 
> the left and right edges of the video stream).
> 
>   I've tried two methods so far, but neither is entirely satisfactory.  
> Can anyone suggest a good approach?

I'm using TV out from a Geforce4 MX440 card. I have a 720x576 50Hz
modeline for X. Then use the TV out overscan controls to have the
picture fill the TV.

By default, the 16:9 picture is letterboxed to fit the 4:3 TV.
You can use the '16:9 Zoom' mode to get the central 4:3 portion
to fill the screen.

My TV is a plain Panasonic 4:3 with nothing but
composite/S-Video/component inputs, so I haven't tried VGA output.

>   Here is what I've tried:
> 
>   i) Use VGA out on the myth box at 640x480x60Hz into the vga in port 
> on the TV.

You should be able to use 50 Hz, which would be better. You need
interlaced output also, which your video card might not support.

>   I then tried the modeline on that website, and the one posted by 
> Stephen Williams on this list:
> 
>   Modeline "768x576pali" 14.76  768 789 858 944  576 580 583 625 -hsync 
> -vsync interlace
>   ModeLine "720x576pali" 13.875 720 744 808 888 576 581 586 625 -hsync 
> -vsync interlace
> 
>   Both of these generate an image that is too large for the TV screen.  
> More than that, changing the mode line by small amounts doesn't seem to 
> help - I'm beginning to wonder if the TV has some auto-centering 
> circuitry that is throwing things off.  sigh.

You might be able to fix this with 'xvidtune', though it might be the
same as the adjustments you already tried by hand.

>   The other problem is that the 'interlace' part of the modeline seems 
> to turn off Xv support (Savage drivers).  This in turn switches off the 
> ability to zoom in Myth - I only get the 16:9 image squished into 4:3.  
> I don't like the stretching.  Again, sigh.

It sounds like a better VGA card is in order.


regards

Hamish
-- 
Hamish Moffatt VK3SB <hamish at debian.org> <hamish at cloud.net.au>