[mythtv-users] Re: Custom Modeline

Jim Sager jim.sager at turner.com
Mon Jul 19 11:42:27 EDT 2004


Excuse my ignorance with respect to modelines. I have read through the 
discussion here and I have a question regarding underscanning the PVR-350 
TV-Out - can it be done using the modeline settings? Basically this is the 
setting that I currently have (found in myth setup documentation):

Section "Monitor"
        Identifier  "NTSC Monitor"
        HorizSync  30-68
        VertRefresh 50-120
        Mode "720x480"
          # D: 34.563 MHz, H: 37.244 kHz, V: 73.897 Hz
          DotClock 34.564
          HTimings 720 752 840 928
          VTimings 480 484 488 504
          Flags    "-HSync" "-VSync"

I currently have myth set to reduce the display size to 624x440 in order to 
fit in the TV screen (also have it running in a window since the x and y 
offsets don't appear to work unless you do so). Can the modeline settings be 
used to reduce the size of the visible picture and produce the correct offset 
to center it on the screen? I am truly showing my ignorance here with respect 
to modeline settings as well as an understanding of the hardware that's 


On Friday 16 July 2004 07:50 am, Cory Papenfuss wrote:
>  	It's certainly not the fault of the modelines that the TV is
> overscanned.  Rather, it's that historically TV pictures have always been
> overscanned and the switch to HDTV apparently hasn't fixed that (?).  If
> you raster the specified visual resolution with the standard timings, the
> picture will be overscanned.  Since you (and I for that matter) are
> essentially driving the TV directly from the VGA port, it's *REQUIRED* to
> output an ATSC standard video signal raster with standard timings.  If
> you're TV is tolerant of something other than that, great... but make sure
> it is by the book or you can blow it up.
>  	With all that said, remember that although the spec might specify
> visual size (e.g. 1920x1080) in addition to the raster size/speed, it's the
> raster that must be correct to avoid TV damage.  Think of the raster as the
> black canvas that's painted at a certain rate consisting of a certain
> number of lines.  For illustrative purposes, I scoured the 'net and found a
> 1080i modeline that does appear to have a 33.75kHz horizonal frequency
> (that appears to the be correct standard rate for 1080i... 45kHz for 720p
> BTW):
> Modeline "1080i" 74.250 1920 2008 2048 2200 1080 1084 1094 1125 interlace
>  	You could use the same modeline, but have a letterboxed 1024x768
> *visual* (upper left hand corner) by modifying it as follows:
> Modeline "test" 74.250 1024 2008 2048 2200 768 1084 1094 1125 interlace
>  	Or try to move it towards the center by 200 pixels H/V:
> Modeline "test" 74.250 1024 1808 1848 2200 768 884 894 1125 interlace
>  	In all those cases, the oscillators in the TV won't change at all...
> just when and for how long the video guns turn pixels on and off.
>  	So if you are trying to vertically "underscan" the mode and can live
> with running a "standard" HDTV raster with a "nonstandard" HDTV
> visual resolution,
> Modeline "test2" 74.250 1920 2008 2048 2200 980 1034 1044 1125 interlace
> will keep the TV happy, and you should have a 1920x980 resolution, with 50
> additional black pixels on both the top and the bottom.  Although it's a
> funky resolution, playing video on a linux box usually uses XV for scaling
> anyway, so it usually scales to fit accordingly.  If you're trying to
> actually play all 1080 lines of a bone-fide 1080i orginal source material
> without losing any lines off the screen, you'll need more than a
> modeline.... like a TV fancy enough to adjust the screen position, or
> unfancy enough to take a screwdriver to it and adjust the raster.
> Cheers
> -Cory
> *************************************************************************
> * The prime directive of Linux:  					*
> * 	- learn what you don't know, 					*
> * 	- teach what you do.						*
> * 						(Just my 20 USm$)	*
> *************************************************************************
> On Thu, 15 Jul 2004, Chris Vargas wrote:
> > Cory: your initial reply to John caught my eye,
> > because I'm in John's same boat. At first I thought
> > I'd be able to correct it given your great explanation
> > of modelines, but now I'm not so sure.
> >
> > I have a 9A60 transcoder (thanks yet again, Jarod!),
> > and am trying to adjust the vertical dimension as
> > well. My 480p modeline plays back anamorphic DVDs
> > correctly, but my 540p and 1080i modelines (derived
> > via Powerstrip) are all stretched too far vertically,
> > so that an anamorphic test pattern displays circles as
> > ovals.
> >
> > Wouldn't I need to add vertical lines to get this
> > compression? I tried using one of your examples to add
> > (say) 40 pixels vertically, but if it's not going to
> > work and blow up my TV, maybe not. Then again, it's 3
> > years old and doesn't do 720p, so maybe I should blow
> > it up...


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