what causes the flicker on a computer or tv screen when viewed through a camcorder or a video recording device

Question

I've noticed that whenever they show a Tv screen or a computer screen(especially) on TV there always seem to be lines going across the screen from top to bottom (except in the highest quality video). Have you noticed that? What causes it?

Answer 1

The TV image refreshes itself top-to-bottom so-many-times per second. The camcorder acquires images at a slightly different number of times per second. The two are out of phase, so the TV image appears to "move."

Answer 2

ive noticed it but dont know what causes it...