[mythtv-users] Hardware for Best TV-Out?
core at enodev.com
Sat Nov 6 03:26:09 UTC 2004
Very cool. Finally got a chance to try out 480p and it worked, though
the picture is slightly too tall, which is par for the course with my
TV. Is it the same idea as adjusting underscan if I want to adjust
vertical screen size/position?
Also, my TV claims to do 1080i, but anything I try for HDTV modelines
out on the net make my screen go compressed and vertical vibrate flippy.
Please forgive the ignorance. I have been trying to get things figured
out myself, but so many supposed HOWTOs sometimes take leaps in logic
via assumptions of prior knowledge.
On Sun, 2004-10-31 at 08:12 -0500, Cory Papenfuss wrote:
> That's only 29.1kHz... a little too slow to be 480p resolution.
> You should start with a standard mode for VGA as given by
> e.g 640x480 at 60Hz
> Modeline "640x480" 25.17 640 656 752 800 480 491 493 524 -hsync -vsync
> 25,170,000 / 800 = 31.4kHz
> Then, if you need more underscanning, change the dotclock and the
> horizonal line width by the same percentage and you'll get another
> modeline with the same frequencies, but different widths of black at the
> edges. Strictly speaking, you should adjust the sync widths as well, but
> practically most monitors don't care so much about it, and you end up
> wanting fracional pixels or something you can't do anyway.. For example,
> adjust for 5% underscanning:
> 25.17*1.05 = 26.428
> 800*1.05 = 840
> Modeline "640x480" 26.428 640 656 752 840 480 491 493 524
> 26,428,000/840 = 31.46kHz
> That'll put lots of black on the left side of the screen, but keep the
> frequency the same. To move the picture to the left side, add some (the
> same amount) to the sync-describing number, keeping their difference the
> same. This adjustment will split the underscanning (which added 40 pixels
> to the line count) equally on the L+R side:
> 656 + 20 = 676
> 752 + 20 = 772
> you're using 640x480, but if you're looking for something higher for 480p,
> you can try a 720x480 with 480p timings e.g.
> ModeLine "480p" 28.6 720 760 824 910 480 484 492 525
> 28,600,000/910 = 31.42kHz (see a pattern here?)
> If you want higher resolutions than 480p, you'll need to find out what's
> acceptable for your TV. I don't have one that'll do any higher than 480p
> so I haven't looked into it. 540p, 720p, and 1080i should all be doable
> if the TV does it, but I won't presume to know anything about the
> modelines to use.
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