I'm not sure what you're changing on your set top box or what type of set top box (or SlingBox) you have but I think I can help.
Try going "View > Video Zoom" and play with the different choices.
I have a SlingBox SOLO hooked up to a standard definition (4:3 not adjustable) set top box that will always display 4:3 either filled or with black bars at the top/bottom. The default is "normal" which works great for 4:3 set top boxes with a 4:3 broadcast but can produce some strange results if the program is widescreen.
My laptop has a 16:9 display so when I watch a program that's broadcasting in 4:3 I use "normal" mode (ALT+SHIFT+N) and it fills from the top to bottom with black bars on the left/right. If you prefer a stretched image, you can try "anamorphic" (ALT+SHIFT+A) but I'd rather see bars on the side than a distorted image.
If I watch a program that's broadcasting in widescreen, the set top box puts bars on the top/bottom which results in a small picture with borders on all sides. To make it fit my laptop screen, I use "letterbox" (ALT+SHIFT+L) which crops the top and bottom off the stream (usually just the top/bottom black bars the set top box puts on to make it 4:3) so it fits a 16:9 display perfectly without stretching.
Thanks I've tried all 5 zoom options and they are all the same.
Anamorphic works the best with the least black bars but they are still there on EVERY channel...
Heres a screenshot of what it looks like:
Is this something to do with my slingbox classic? If I upgraded to slingbox pro and hooked it up via hdmi would this make any difference at all and get rid of the black bars?
That's odd, I'm not sure what to say. I've only ever used a SlingBox SOLO so hopefully somebody else can answer your question.
Here's what I see in the different views, I think this is Storm Stories (or something) on The Weather Channel that's all I could find right now in widescreen on the channels we get:
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