[mythtv-users] 1920x1080i source on 1920x540p output, video is narrow

[Doug Larrick]

On Wed, 7 Apr 2004, Daniel Walton wrote:
>  "848x480" 36.789 848 944 1024 1088 480 509 515 563 +hsync +vsync
>  "960x540" 40.806 960 1056 1136 1216 540 550 551 563 +hsync +vsync
>  "1920x540" 80.986 1920 2064 2256 2416 540 547 548 563 +hsync +vsync
[snip]

John Patrick Poet wrote:
> Here is what I use (thanks to Doug Larrick):
> 
> # 960x540 progressive, pseudo-1080i
> Modeline "540p" 39.956 960 1020 1100 1184 540 550 551 563 +hsync +vsync # 39.956 MHz 33.75 kHz 59.94 Hz
> 
> # 1920X540 progressive, pseudo-1080i, 2x 540p's H timings
> Modeline "540pw" 79.912 1920 2040 2200 2368 540 550 551 563 +hsync +vsync # 79.912 MHz 33.75 kHz 59.94 Hz

Indeed, Daniel, you'll notice that your 1920x540 modeline's H values 
(the first 4 integers) are not 2x the better-working 960x540 H values. 
Indeed, your modelines work out to:

848x480:  36.789 MHz dotclock, 33.81 kHz hrefresh, 60.06 Hz vrefresh
960x540:  40.806 MHz dotclock, 33.55 kHz hrefresh, 59.60 Hz vrefresh
1920x540: 80.986 MHz dotclock, 33.52 kHz hrefresh, 59.54 Hz vrefresh

Those H refresh values are close enough to 33.75 kHz that your TV senses 
"1080i" and switches to that mode.  But your V refresh values are off 
from the broadcast standard of 59.94 Hz just enough that you'll get a 
video stutter every once in a while.  But I don't see anything here that 
would cause severe underscan.

You definitely *need* a DisplaySize option for the 1920x540 mode -- it's 
the only thing that tells Myth that your pixels aren't square (in fact, 
they're twice as high as they are wide).  Without this option you'll 
definitely see a half-size picture horizontally centered on the screen.

TVs, even HDTVs, are set up to overscan so they cut off any noise at the 
edges of the picture, or geometry problems with the CRT -- as opposed to 
computer monitors, which are set up to underscan so you can see the 
whole picture.  In order to use an HDTV as a computer monitor, you'll 
have to use a "subset" mode like your 848x480 one, though I'd suggest 
getting the "pure" modes working properly first.  Actually I'd suggest 
just cribbing mine :-)

-Doug
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