You probably were "out of bounds". Time to introduce two terms.
Underscan and overscan. This is a fallback to old television
standards.

http://www.seriousmagic.com/products/dvrack/DVRack2OnlineHelp/F_US__Underscan-Sa
fe.htm

When you view a video frame on a computer you typically see the WHOLE
frame including what will often fall in the underscan area. This can
often include video noise at the top or bottom of the video frame.

So to avoid this getting included in the finished product better video
editing software automatically can switch between showing the whole or
raw frame and what typically will show on a TV screen.

Two more terms: Action Safe and Title Safe areas.

As a general rule of thumb Action Safe is a border 10% from the edge
around the entire video frame while Title Safe is between 15-20% from
the edge. The idea is make sure your photos or video falls within this
boundary to avoid cutting off heads and parts of titles. Action safe
is more appropriate to where some hot spot can appear on a clickable
menu like for a DVD. If somebody makes a button that is suppose to be
clicked on to change chapters it can be practically even fully off
screen if too close to the edge, so obviously something you want to
avoid.

The problem is all tvs are slightly different and more so if they are
poorly calibrated or suffering from high voltage blooming which is an
effect that will cause the entire picture to "bloom" or expand thus
filling out the screen more than it should due to the signal getting
fed too much high voltage, this is quite common in aging CRT style
TVs.