Edgar Bailey, age 15, of Pittsfield, Mass., for his question:
HOW IS A VIDEO RECORDING MADE?
A video recording is the process of recording still or moving images electronically, rather than photochemically as in photographic film. The techniques used to record images on videotape are similar to those used to record sound.
Electronic signals from a television camera, or from a television camera via a TV receiver, are stored as patterns of magnetized regions of iron oxide on so called magnetic tape. When the recorded tape is played back, the original signals are generated. These signals can then be disseminated by broadcast antenna or by cable to television receivers that translate the signals into images and sound.
Video tape recorder playback systems for domestic use are connected directly to a television receiver.
Unlike motion picture film, videotape does not require processing and so may be played back immediately. This makes possible the so called instant replay common to television sporting events.
In 1956 a transverse scanning system of video recording and playback was developed. In this system, called quadriplex, four record playback tape heads are mounted on the circumference of a drum that rotates rapidly at a right angle to the direction of tape movement.
The quadriplex system is used almost exclusively by the broadcasting industry. Another scanning principle is used in video recorders manufactured for domestic use. This simpler system, called helical scan (or slant track scan), has a much slower head to tape speed than the quadriplex system.
Video cassette recorders (VCRs) became relatively inexpensive by the early 1980s and were commonly sold for domestic use. The earliest home videotape recorder was a reel to reel type but then engineers developed the less expensive cassette videotape recorder.
In helical scan, one or two record playback heads are mounted on the circumference of a drum that rotates rapidly in the same direction as the tape transport. The tape is wrapped around the drum in a helical manner. The wrap angle (that is, the angle between initial and final contact with the drum) is anywhere from 90 degrees to 360 degrees, depending on the make of the recorder.
Most helical scan systems employ tape widths of 1.25 centimeters or 1.9 centimeters housed in tape cassettes.
Videodiscs were developed as a response to the high cost of magnetic tape in the 1960s and early 1970s. Nonmagnetic discs most commonly allow only the reproduction of prerecorded material but one advantage they have over tape is the rapid access they offer to any part of the recording.
Videodisc sales are far lower than those of VCRs. Today CD’s and DVD are in common use by all populations young and old.