In North America the video signal is a standard, called NTSC, and is not the same as computer, or RGB video.
Video is a linear medium like audio, unlike photography or film.
A film camera captures the entire frame of a picture in a single instant. But video was originally designed to be transmitted over the air. Images must be broken up and transmitted or recorded as a series of lines, one after the other. At any given millisecond, the video image is actually just a dot speeding across the face of the monitor glass. Television is also primarily an analog medium.