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Video recording
Magnetic tape

VCR
The recording of video signals on magnetic tape was a major technological accomplishment, first implemented during the 1950s in professional machines for use in television studios and later (by the 1970s) in videocassette recorders (VCRs) for use in homes. The home VCR was initially envisioned as a way to play prerecorded videos, but consumers quickly discovered the utility of recording shows off the air for later viewing at a more convenient time. An entirely new industry evolved to rent videotaped motion pictures to consumers.
The challenge in magnetic video recording is to capture the wide range of frequencies present in the television signal—something that can be accomplished only by moving the recording head very quickly along the tape. If this were done in the manner of conventional audiotape recording, where a spool of tape is unreeled past a stationary recording head, the tape would have to move extremely fast and would be too long for practical recording. The solution is helical-scan recording, a technique in which two recording heads are embedded on opposite sides of a cylinder that is rapidly rotated as the tape is drawn past at an angle. The result is a series of magnetic tracks traced diagonally along the tape. The writing speed—that is, the relative motion of the tape past the rotating recording heads—is fast (more than 4,800 mm, or 200 inches, per second), though the transport speed of the tape through the machine is slow (in the region of 24 mm, or 1 inch, per second).
The first home VCRs were introduced in the mid-1970s, first by Sony and then by the Victor Company of Japan (JVC), both using 12-mm (one-half-inch) tape packaged in a cassette. Two incompatible standards could not coexist for home use, and today the Sony Betamax system is obsolete and only the JVC Video Home System (VHS) has survived. Narrower 8-mm tape is used in small cassettes for handheld camcorders for the home market.

DVR
The first magnetic video recorder for professional studio use was introduced in 1956 by the Ampex Corporation. It utilized magnetic tape that was 48 mm (2 inches) wide and moved through the recorder at 360 mm (15 inches) per second. The video signal was recorded by a “quadruplex” assembly of four rotating heads, which recorded tracks transversely across the tape at a slight angle. Television programs are now recorded at the studio using professional helical-scan machines. Employing 24-mm (1-inch) tape and writing speeds of 24,000 mm (1,000 inches) per second, these have a much greater picture quality than home VCRs. Digital video recorders can directly record a digitized television signal.
In home videocassettes, the recorded signal is not in the formats described in the section Compatible colour television. Instead, the wave forms are converted to a “colour-under” format. Here the chrominance signal, rather than modulating a colour subcarrier located several megahertz above the picture carrier, is used to amplitude modulate a carrier at about 700 kilohertz, while the luminance signal frequency modulates a carrier at about 3.4 megahertz. The two modulated carriers are then added together for recording as a single composite signal.
Video discs
Perhaps the first recording of television on disc occurred in the 1920s, when John Logie Baird transcribed his crude 30-line signals onto 78-rpm phonograph records. Baird’s Phonovision was not a commercial product, and indeed he never developed a means to play back the recorded signal. A more sophisticated system was introduced commercially in 1981 by the Radio Corporation of America (RCA). The RCA VideoDisc, which superficially resembled a long-playing phonograph record, was 300 mm (12 inches) in diameter and had spiral grooves that were read by a diamond stylus. The stylus had a metal coating and moved vertically in a hill-and-dale groove etched into the disc, thereby creating a variable capacitance effect between the stylus and a metallic coating under the groove. The marketing philosophy of the VideoDisc was that consumers would want to watch videos in the same way they listened to phonograph recordings. However, the discs could not be recorded upon—a fatal flaw, because the VCR had been introduced only a few years earlier. RCA withdrew its disc from the market in 1984.
An optical video disc was developed by Philips in the Netherlands and was brought to market in 1978 as the LaserDisc. The LaserDisc was a 300-mm plastic disc on which signals were recorded as a sequence of variable-length pits. During playback the signals were read out with a low-power laser that was focused by a lens to form a tiny spot on the disc. Variations in the amount of light reflected from the track of pits were sensed by a photodetector, and electronic circuitry translated the light signals into video and audio signals for the television receiver. By using optical technology, the LaserDisc avoided the physical wear-and-tear problems of phonograph-type video discs. It also offered very good image quality and achieved limited success with consumers as a high-quality alternative to the home VCR. However, like the RCA VideoDisc it could not be recorded upon, and its analog representation of the video signal prevented it from offering the interactive capabilities of the emerging digital technologies.
A new approach to optical video recording is represented by the digital video disc (DVD)—also known as the digital versatile disc—introduced by Sony and Philips in 1995. Like the LaserDisc, the DVD is read by a laser, but it utilizes MPEG compression to store a digitized signal on a disc the same size as the audio compact disc (120 mm, or 4.75 inches). Programs recorded on DVD offer multiple languages and interactive access. DVD is truly a multiple-use platform, in the sense that the same technology is used in personal computers as an improved form of CD-ROM with much greater storage capacity.