[mythtv-users] overscan problems with nvidia 8400 GS

Mike Perkins mikep at randomtraveller.org.uk
Tue Jul 14 11:43:00 UTC 2009

Simon Hobson wrote:
> Matthew Harrison wrote:
>> I suppose a more usefull question is: Have broadcasters stopped 
>> letting junk into the edges of their transmissions to allow us to 
>> safely reduce overscan?
> With digital there is no reason for there to be any junk. There is no 
> need for any signalling, and no need for any guard areas to separate the 
> picture from non-existant sync and colour phase signals.
> As I mentioned earlier, I've been watching UK Freeview for several years 
> without overscan and never noticed anything untoward. Since they don't 
> transmit a test card any more I can't be certain, but from the location 
> of the squigglies (channel logo), it certainly looks like I'm getting 
> the full image including the bit that's normally off the tube. The only 
> annoying thing is having the squigglies a long way into the picture - 
> made worse by them being positioned to be visible on a 4:3 set with the 
> edges cropped as well as overscanned.
> With an all digital setup, overscan makes no sense. Anything converted 
> from analogue could be overscanned at source. I guess we're stuck with 
> this historical artifact from the quickly vanishing days of CRT displays.
Interestingly, I also watch primarily Freeview. My TV has a VGA input as well as 
two Scarts and two s-video inputs. My mythbox is connected to the VGA input usually.

I have, however, tried it both with a VGA-to-Scart adaptor, and with an S-Video 
to Scart adaptor. With VGA, what you see is definitely what you get, it behaves 
exactly like a 1366x768 computer monitor, pin-sharp. With other inputs, there is 
obvious overscan and the picture is softer, although still acceptable to the 
layperson's eye. I don't know whether that's a function of the video driver or 
if the TV is reconverting the picture to overscan it.


Mike Perkins

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