[mythtv-users] NTSC ModeLine

Ryan Steffes rbsteffes at gmail.com
Thu Sep 2 21:21:35 EDT 2004


Since you seem to know a ton more than me, do you know any generic
reason why a tv-out card would cause the tv to look like it's got a
houndstooth pattern (for lack of a better description) over top of a
washed out version of what the picture should be?

I've got a Radeon 7000 that I just can't get a picture out of and it's
driving me nuts.

On Thu, 2 Sep 2004 19:41:46 -0400 (EDT), Cory Papenfuss
<papenfuss at juneau.me.vt.edu> wrote:
>         It's more complicated than that (of course!).  The 480 is required
> (well, actually 525 total scanlines.. lots of 'em blank) for NTSC.  The 640 is
> *NOT* a specification, but rather the resolution at which the aspect ratio is
> 4:3 just like NTSC.  Only horizonal frequency (and sync pulse widths) determine
> the horizonal resolution for NTSC.
> 
>         Pretty much all tvout cards have some funky hardware to match the video
> card's VGA output to the NTSC requirement.  You may be right that it doesn't
> have a scaler, so it needs 4:3.  What it most certainly will have (if you're
> running it out of a tvout card on svid or composite) is a frame-buffer
> resampling.  The NTSC spec requires 29.9Hz/15.7kHz, so it's gotta parse through
> the video ram at that speed.
> 
>         My advice on TVOUT cards is use 'em if you got 'em, but you're probably
> best off to stick with a standard modeline.  Don't try to get the one that
> "matches NTSC," because there is no such thing (except with component out the
> VGA port or similar).  Run with an 800x600 (4:3), maybe tweak the
> over/underscan if the tvout card will let you customize, and be done with it.
> There's too much going on under the scene that you don't have control over to
> make it "perfect."
> 
> -Cory
> 
> *************************************************************************
> * Cory Papenfuss                                                        *
> * Electrical Engineering Ph.D. Graduate Student                         *
> * Virginia Polytechnic Institute and State University                   *
> *************************************************************************
> 
> 
> 
> 
> On Thu, 2 Sep 2004, Shaun Jackman wrote:
> 
> > I've having a lot of trouble getting TV out to work with my G550. From
> > what I understand, the G400 had hardware to scale down whatever
> > resolution you were using to NTSC. The G550 doesn't include this
> > hardware, so the precise TV resolution must be used. I think 640x480
> > should be good, but I wasn't sure if it should be normal 640x480 at 60p
> > or interlaced, or NTSC, or what. So, I'm trying all of them. You're
> > right though. It's time to get on with life.  ; )
> >
> > Cheers,
> > Shaun
> >
> >
> > On Thu, 2 Sep 2004 18:21:15 -0400 (EDT), Cory Papenfuss
> > <papenfuss at juneau.me.vt.edu> wrote:
> >>         I wrote awhile back about modelines... check the archives and the wiki.
> >> In short, here's what I use, and it produces precisely NTSC spec (or at least
> >> the SDTV that I use thinks so)
> >>
> >> Modeline     "coryntsci"  14.318 720 760 824 910 480 484 492 525 interlace
> >>
> >>         I always hated that error message in X, because there's a big
> >> difference between a bad mode due to "clock" or "interlace" or "doublescan".
> >> You're using a Matrox card (MGA), and my experience has always been excellent
> >> with linux, custom modelines, interlaced, sync-on-green, and all sorts of
> >> nasties I could throw at it.
> >>
> >>         Check elsewhere in the logs for a "Dotclock range 12.0-250Mhz" to rule
> >> out that.  Try a standard VESA interlace modeline (e.g. 1024x768 at 43) to see if
> >> the card doesn't do interlace... some don't.
> >>
> >>         Of course, the obligatory question... why are you doing this?  Do you
> >> have a component tv that only does 480i or something?  VGA monitors don't do
> >> NTSC, but they will do double.  If you're using a standard tvout card, double
> >> the frequency, remove the interlace, and get on with life.  :)
> >>
> >> -Cory
> >
> 
> 
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