A 4:3 stream will display at a factor of 4:3. If you monitor is 16:10 it will always have a black border.
put your desktop resolution in the tool above.
1024x 768 is 4:3 and on a 16:10 monitor using the device (monitor) scaler will give you black left and right borders on your Monitor but will fill the desktop when in full screen
The sling displays 4:3, 8:3 or 16:9 a 16:10 screen will have borders somewhere