[mythtv-users] NTSC ModeLine

Cory Papenfuss papenfuss at juneau.me.vt.edu
Thu Sep 2 19:41:46 EDT 2004

 	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 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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