The idea is, you just move the little corner frames to indicate the limit of your screen and, hey presto, your screen real estate is set perfectly. Well, that's the idea anyway. I've never seen this damned thing work. So, after a lot of mucking around, trial and error, I came up with a formula to make it work. Your mileage may vary but, It Works For Me.TM
So for anyone interested, and for next time I have to go through this....
Before you start, you will need:
c. Your video driver running the correct / latest display drivers. Ie, you should be able to watch a movie with sound before trying this.
1. Start by going to the Screen Wizard (seriously.... just for this step) - so navigate to Setup > Screen Setup Wizards - and move the left/top corner bracket ONLY until it's evenly a little way out from the corner - that is, the white is out from the corner, maybe 1 cm. For mine, this was moved until the Offset value was 44x26 - that's all we are lookin at in this step. The right and bottom edges of the screen at this point WILL be cut off the edge of the screen. Leave it as it is. DO NOT try to move the bottom/right bracket. It may seem to work.... right up until you save the settings and restart. Go ahead, try it. When you are sick of it - and assuming haven't thrown a chair through the TV screen, carry on from here.
2. So after changing the top/left bracket ONLY as described above, press m(enu) key and save the settings.
NOTE: at any point along the way you can go back to the 'Wizard', press the M key and select reset to take you back to the default settings.
3. Quit out of mythbuntu frontend and restart.
4. Once back in the frontend, go to Setup > Appearance and then adjust all four GUI and Offset values until the settings work for your screen. Do this a little at a time and to check your work, click next... finish until you get back to the menu system. As it goes back to the menu system you will notice the screen resize / jump to the new settings. Now go back to the Appearance window and use its window border to assess the settings you've made so far. Be sure to take note of the amount of black space around the image, taking care not to create a gap between the screen image and the TV's bezel.
5. Repeat until the settings give you a display that works well for your TV.
6. For my TV, running at full HD (1920x1080), the settings found to be best were:
GUI Width: 1825
GUI height: 1036
GUI X Offset: 48
GUI Y Offset: 24
Hope that helps someone else/
Edited by Scootre, 20 May 2012 - 12:38 AM.