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

[Daniel Walton]

On Thu, 8 Apr 2004, Doug Larrick wrote:

> 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.
>

I have overscan, its just that when myth or xine play the video the picture is
really narrow.  Sounds like you may have figured out why in the next paragraph.

> 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.
>

That is good to hear.  I'll give this a try and get back to you.

Daniel

> 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
>