Overscan and broadcast television  by Billy Biggs
<vektor@dumbterm.net>  I often get asked about the overscan
setting in tvtime. This webpage was written to help explain how
different television broadcasters use the overscan properties of
televisions.  What is overscan?  In an NTSC television signal,
there are 486 scanlines on which you can put an image, and in
digital video there are usually 720 pixels on each scanline.
However, on your television not all of this image is visible.
The border of the image extends past the image you see on your
screen. The part of the image you can't see is the overscan.
The raw frame What you end up seeing  What is in the overscan?
Mostly crap. Ideally, you want to keep image in the overscan
from every video signal to allow for post processing filters
downstream to not have to deal with the edges of the image. It
really depends though what you end up seeing. Usually, you just
get some black borders on the left and right sides like this:
Black borders  Other times you see c