The concept of using principles from music synthesizers to design electronic instruments that produce video images. Experimental video has been around nearly since the beginning of television, but prior to the 1960s, the capabilities of the equipment to do anything other than straight broadcast of camera images was extremely limited. Although pioneers started to develop equipment in the 1960s, it was not until the mid-1980s that the equipment started to become affordable to most artists. Also, prior to the 1980s, distribution channels for experimental video did not exist -- there was no consumer video recording or playback medium, and scarce broadcast channel bandwidth was allocated to more mainstream fare.
A key insight in the 1970s was to apply the concept of voltage control to parameters of video generation and processing, e.g., brightness, hue, and color saturation. Devices analogous to a VCO generate certain basic patterns, which can be altered by modulating them in ways conceptually similar to audio modulation, using control signal generators analogous to LFOs, envelope generators, sequencers, etc. Video inputs from cameras and other external sources can also be processed and have control information extracted from them, in a manner that resembles a pitch-to-voltage converter or an envelope follower.
However, unlike audio -- where any signal is reproducible -- a video signal must maintain certain conventions for frame and scan synchronization; otherwise, the resulting signal will not be usable. This means that signal generators must be able create properly formatted signals, and signal modifiers cannot alter the synchronization information in an arbitrary fashion. This creates some difficulties as compared to audio processing, such as the need to "genlock" all of the components in a video synthesizer. Methods for doing this are well standardized in the broadcast industry, but video synthesis puts additional demands on the standards that they were not designed for. Because of this, standards are still being worked out in the video synthesis community, particularly in regard to digital broadcasting. The equipment remains more expensive and more difficult to learn than analogous music synthesizers, and so video synthesis has not yet grown as much as electronic music.