[Jackie78]

Hello,

I use the latest DX build, on a system with AMD 780G Chipset, attached via HDMI to a 40" FULL HD TV. When playing 720p MKV files, I have a black border on all 4 edges of the frame, and when I try to increase the image size, the image only increases inside the rectangle, but never getting bigger, the same is true when I try to calibrate the screen. It is as if underscan is enabled in the Catalyst drivers, which isn't the case.

Do you have any idea how this can be fixed?

[joshuass]

if the tv switched refresh rates, then yes it is due to underscan

A little annoying with ATI CCC: Underscan/Overscan values are dependent on resolution and refresh rate.

To fix, make sure to set the scan values for each refresh rate your TV supports. I did that, and it seems to work quite well.

[Jackie78]

HI joshuass,

yes I know that, but I have set the underscan to 0% in all resolutions and all refresh rates. I have checked in my TV, the resolution is 1920x1080 @60Hz, and it happens anyway

Edit: it seems to be somehow related to changing refresh rate, when I disable refreshrate changing, the problem does not appear. However, it must be somehow set to only a slightly different mode than normally, because in Windows. 1920x1080@60Hz is border-free. But as soon as the video starts, my TV still shows 1920x1080 @60Hz, but something must have changed. It must be some resolution not available in CCC, because I have selected every single resolution that I can select there and set Underscan to 0%. Is there a way to limit XBMC to specific settings for refreshrate changing?

[joshuass]

Try a different build. Some early DX builds had an issue with detecting the size of the window and stuff. Or, wait until Alpha 1 of the next release comes out, which will be shortly (from what I've heard).

[Jackie78]

Hi,

I have downloaded the very latest DX build I could find (24167), obviously there is only a very slight timing parameter changed. Is there any way to globally disable that underscan-crap by ATI (why the hell do they do that by default at all? Every decent TV is able to display 1080p without overscan anyway!) by registry key? It's a pain after each driver-reinstall to set the underscan to 0 for each and every refreshrate. Or is there a way to limit CCC or XBMC to only use a very small subset of resolutions that the user allows?

[joshuass]

The resolution of XBMC doesn't change from whatever your desktop uses. Its the refresh rate that changes. So if your in 1920x1080 then you'll stay in that res.

Now most movies are around 24fps or sometimes 30fps. XBMC uses 60fps (usually because the TV supports a maximum 60Hz horizontal refresh). So that really just leaves you with two resolution/rate combinations you need to make sure are not underscanning (30fps doesnt really count because its easily devided into 60)
1920x1080 @ 24Hz
1920x1080 @ 60Hz

This assumes you don't have any PAL sourced material (25fps and 50fps). If you do then you can add two more to the list:
1920x1080 @ 25Hz
1920x1080 @ 50Hz

All you should have to do switch the rate, apply, set underscan, apply and then switch to the next one until all are done. Also, make sure the check box below the slider for underscan is unchecked.

There have been reports in the AMD forums of this setting reverting back to default so if the above isn't working, disable the Adjust Refresh Rate and go from there.

If you're still have trouble, you'll need to google for registry stuff, as I have no idea about it.

Finally, the reason underscan/overscan exists is because early model HDTV weren't able to accurately handle HD at a 1:1 pixel mapping. TV's that don't have exactly 1920x1080 px panels have to interpolate to reach hi-def resolutions, thats where underscan/overscan comes into effect. It can help the GPU render the screen image to the panel accurately.