Charles Ginsburg led an Ampex research team to develop one of the first practical video tape recorders (VTR). Video was originally exclusively live technology. Video technology was first developed for mechanical television systems, which were quickly replaced by cathode-ray tube (CRT) television systems. Video, by contrast, encodes images with electromagnetic waves. Video was invented decades after film, which records a sequence of miniature images visible to the eye when the film is physically examined. See also: Analog television and Videotape NTSC composite video signal (analog)