[mythtv-users] Stupid overscan question

[Ben Dash]

I think that I may need to tweak fbset as documented
here:

http://forums.xbox-scene.com/lofiversion/index.php/t377567.html

--- Cory Papenfuss <papenfuss at juneau.me.vt.edu> wrote:

> > So are you saying that I should use something else
> > instead of 640x480?  If so then what would you
> > suggest?
> >
>  	What I'm saying is that if you're using a "tvout"
> card, what your 
> computer renders is only loosely related to what
> shows up on the TV.  The 
> signal to the TV *MUST* be NTSC-compliant.  That
> means *exactly* 525 lines 
> drawn every 1/29.97th of a second, where each line
> takes exactly 
> 1/15,734th of a second.  The 640x480 pixels the
> computer is rendering is 
> likely being spatially interpolated (in both horiz
> and vert dimensions) by 
> the tvout chip on the video card so 1 pixel rendered
> != 1 pixel displayed.
> 
>    The number of visible horizontal pixels can be
> just about anything, so 
> long as it take 1/15734th of a second to draw a
> whole line's worth of 
> them.  One can pad the modeline horizontally to make
> 640 or 720 or 
> whatever "visible" pixels visible.
> 
>    The number of vertical lines is *fixed* at 525/2
> per field... If 
> you draw 480 of them (the generally accepted number
> of "visible" lines for 
> NTSC), the TV will draw some of them off the top
> and/or bottom screen so 
> you cannot see them.  If you use a "640x465"
> resolution, the video player 
> will scale the presumably 480-line source into
> 465-line output.... now the 
> video's been abused.
> 
>  	Bottom line, overscanned is the way TVs have been
> mal-adjusted 
> forever.  The *correct* way to not have overscanning
> is to adjust the TV 
> so it doesn't do it.
> 
> -Cory
> 
> 
> > I know that my TV is capable of displaying a
> picture
> > which fills the screen without the top being
> slightly
> > narrower than the bottom since the normal antenna
> > input does so, as does the xBox boot screen.  I've
> > noticed that some xBox games have this resolution
> > problem while some do not.  I'm sure that there's
> some
> > setting in xorg.conf that will fix this but I am
> not
> > familiar enough with TV out to figure out what.
> >
> > Please let me know if you have any ideas,
> >
>  	Sounds like poor geometry control on the TV if
> it's not a 
> rectangular picture.  Again... overscanning hides
> such misadjustments.
> 
> -Cory
> 
> -- 
> 
>
*************************************************************************
> * Cory Papenfuss                                    
>                    *
> * Electrical Engineering candidate Ph.D. graduate
> student               *
> * Virginia Polytechnic Institute and State
> University                   *
>
*************************************************************************
> 
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