VIDEODISC

Videodiscs are records that play high fidelity sound and pictures through conventional television receivers. The dominant videodisc technology is the LaserDisc (LD), a replay-only video disc system based upon the same laser-read optical disc technology used by the compact disc digital audio format. LaserDisc has also been referred to by the terms LaserVision, DiscoVision, and CD-Video. The competing format, known as Capacitance Electronic Disc (CED) has become obsolete in the home market.

Videodiscs produce a picture with 400 horizontal lines, imparting a clearer, sharper image than the 240 lines displayed by conventional videotape. The LaserVision system has two speeds: Constant Linear Velocity discs play for 60 minutes per side, and Constant Angular Velocity discs play for only 30 minutes per side. Both CLV and CAV discs can be played on all LV machines, but the CLV format does not support freeze-frame and other special effects. The obsolete CED system employed discs with a capacity of one hour per side.

The first consumer videodisc players were developed in Britain during the late 1920s by John Logie Baird. Baird's system, known as "phonovision", had only 30 lines of resolution. The capacitance system was developed in the 1960s and was used in commercial broadcasting applications prior to the development of videotape. Capacitance systems were able to play full bandwidth images by means of a stylus riding in the grooves of the videodisc that translated variations in electrical capacitance into video and audio signals. Laser optical disc technology, which uses a laser beam rather than a stylus to play back sound and video images, was developed jointly by MCA and N.V. Philips in the early 1970's. Their collaboration resulted in the DiscoVision system under the Magnavox label .

Initially, videodisc players failed to be widely adopted by consumers. This was due in part to the small number of prerecorded titles offered that could be played on the systems, and in part to the competing technology of video cassette players which allowed consumers the additional ability to record video as well as play back prerecorded products. Their recent resurgent popularity may be traced to improvements in videodisc players, large screen television sets, and improved home sound systems, as well as by increased demand by consumers for a better quality picture. Film buffs and collectors are also attracted to the longer product life of videodiscs: since the audio and video information is protected under an acrylic shield and no stylus or head makes physical contact with the laser disc surface, it is less subject to wear and tear than conventional videocassettes. There are just under 1,000,000 videodisc players in home use in the United States (compared to 85,000,000 VCRs), and over 2 million units in Japan.

 

Although the LD video disc's shiny acrylic surface resembles that of digital audio compact discs (CDs), the laser disc differs in that it may be encoded with both analog and digital data. Most videodisc players are thus able to playback both digital and analog sound. Many videodiscs released now incorporate a digital audio soundtrack which uses exactly the same standard used by compact discs. However, most players still support the analog soundtracks of older discs released from between 1978 and 1986. Many LD format videodisc players are also able to play conventional digital audio compact discs. Videodisc players often have features similar to those found on CD players, such as track numbers (known as "chapters" in videodisc terminology), real time counters and rapid random access or direct access to any chapter on the side by chapter number or by specific time.

In comparison with North America and Japan, the market for videodisc players in PAL territories is still small. Since videodisc players must store a complete video signal, they are engineered in accordance with one of two incompatible formats, either the 525 line NTSC system or the 625 line PAL system. Fortunately the further sub-division of the 625 line based systems into the PAL and SECAM color systems was avoided: color information that is recorded on the disc in the PAL color system is internally decoded into SECAM by players meant for this market. NTSC videodisc players are the norm in many South-East Asian countries despite their use of the PAL standard for local television broadcasts. However domestic videodisc releases for the PAL color system are made in Europe and Australia, but this small market is not well developed and fewer titles are available on disc. This has encouraged the videodisc player manufacturers to begin the production of dual standard players.

-Aviva Rosenstein

FURTHER READING

Lenk, John D. Lenk's Laser Handbook: Featuring CD, CDV, and CD-ROM Technology. New York: McGraw Hill, 1992.

Pratt, Douglas. The Laser Video Disc Companion. New York: Zoetrope, 1988.

Rovin, Jeff. The Laserdisc Film Guide: Complete Ratings for the Best and Worst Movies Available on Disc. New York: St. Martin's, 1993.