Black Borders Appear Around TV Video

When I output to a TV, why are there black borders around the video?

The black borders you see on your TV screen are caused by underscan from the TV encoder on your graphics card.   Underscan occurs when a video signal does not reach the edges of your monitor and leaves a black border around the image.

Normal broadcast TV content is "overscanned," meaning the image bleeds/scans past the edges of the screen so it fills the entire monitor. PC CRT monitors usually will have a 1" border which is not viewable.  LCD PC monitors are not overscanned. 

Video cards compensate for this by creating a black border, which you don't see, to fill the border that is not visible.  This black border appears on your TV.  A feature called Resize Desktop in the NVIDIA Control Panel can compensate for this TV / HDTV limitation. 

See also Setting Up NVIDIA Graphics Card to Work with HDTV