[mythtv-users] Custom Modeline

[Cory Papenfuss]

>> 
>>     As another example, if one wanted to construct an underscanning mode, 
>> how would one use the 'videogen' tool without already knowing *exactly* 
>> what mode he wanted anyway?  How about shifting the picture 
>> up/down/left/right? Hrm... maybe I aught to write my own utility or add to 
>> videogen.... :)
>
> What's underscanning? why would I want that?

 	TV is overscanned... some of the picture is blown off the sides of the 
monitor.  Computer monitors are underscanned... the entire picture fits on the 
tube, and has some small black bars around it.  If you're using TVOUT, there's 
often a TVOverScan option in the config you can use to try to compensate for 
this.  If you are cooking up your own modelines, you can make it underscanned 
by making the active picture smaller, and increasing the blanking intervals by 
the same amount.

Modeline coryntsci 14.318 720 760 824 910 480 484 492 525 interlace
 			    40  64  86

can be converted to 640x480 (with black bars on the sides) at *exactly* the 
same frequency specifications by making the visible 80 narrower, and the blank 
parts 40 and 40 wider:

Modeline coryntsci 14.318 640 720 784 910 480 484 492 525 interlace
 			    80  64  126

If you're using a vid card with tvout without the ability to overscan via 
custom options (like the nvidia drivers have), you could use this technique to 
manually fry up an underscanned line based on a standard size like 800x600.

-Cory