SelectaVision
From Free net encyclopedia
SelectaVision was originally the name for a video playback system developed by RCA using specialized CED media, in which video and audio could be played back on a TV using a special analog needle and high-density groove system similar to phonograph records.
The format was commonly known as "videodisc", leading to much confusion with Laserdisc format, which is mutually incompatible with this format.
The name "SelectaVision" was also used for some early RCA brand VCRs.
Contents |
Development and Lifespan
The SelectaVision format was first developed in the 1970s by RCA and first sold in 1981 in the United States and Canada. Player manufacturing was discontinued in 1984, while disc manufacturing ended in 1986 along with the acquisition of RCA Corporation by General Electric.
First prototypes of CED discs were multilayered, implementing a nickel substrate within the platter. However, premature failure of the multilayer discs, usually from separation of the layers and resulting in damage to the player if a disc in such condition was played, forced RCA to search for solutions to the problem or alternative materials to crafting the disc. The final disc would be crafted using PVC blended with carbon to allow the disc to be conductive. To preserve stylus and groove life, a thin layer of silicone was applied to the disc as a lubrication aid.
CED videodiscs were originally meant to be handled by hand. But, during testing, it was shown that people could accidentally touch the signal surface of the disc, causing signal degradation on the affected area. Thus, the idea of enclosing the disc in a caddy which should be extracted only by the player was developed.
How SelectaVision Worked
SelectaVision used a special medium known as a Capacitance Electronic Disc (CED). The VideoDisc was a 12 in (305 mm) platter housed in a special caddy. The video and audio signal is stored on the Videodiscs via peaks and valleys in the grooves, similar but not exactly like a phongraph record, of both sides of the discs. To play a Videodisc, you inserted the caddy into the player and the platter would be extracted. A keel-shaped needle with a titanium electrode layer would ride in the groove with extremely light tracking force, reading the electrical signal from the groove where it is decoded back into its FM state.
Unlike a phonograph record, where physical movement (vibration) of the stylus in the groove of the platter led to an audio signal, the stylus in a SelectaVision player slid along the crests of the groove, at a constant rotational speed of 450 rpm. The varying undulations of the peaks and valleys in the groove provided differing amounts of capacitance between the stylus and the conductive carbon loaded PVC disc. This varying capacitance was measured by the player circuitry, providing an audio/video signal.
Also unlike a phonograph record (and more like a floppy disk), the grooves on a CED did not consist of a single groove in a spiral, but of concentric grooves, each containing a fixed amount of audio/video time (8 interlaced video frames, or 4 complete video frames—1/15 of a second).
The disc is stored inside the caddy. On the inner edges of the outlet of the caddy, there are felt strips designed to catch any strands of fiber or dust that could be on the disc before it is extracted. The disc itself is surrounded by the "spine", a plastic ring (actually squarish on the outside edge) with a thick, straight rimlike edge, which extends outside of and latches into the caddy, serving as a cover. When the disc is inserted into the player, both the disc and the spine are extracted from the caddy and contained inside.
Features of SelectaVision
Like VCRs, SelectaVision videodisc players had features like rapid forward/reverse and visual search forward/reverse. They also had a pause feature which blanked the screen as CED could not perform freeze frame. Since they were a disc based system, they did not require rewinding. Early discs were generally monaural but later discs included stereo sound. Other discs could be switched between two separate mono audio tracks, providing features such as bilingual audio capability.
Each side of a CED disc could be split into up to 63 "chapters", or bands, which on some later players could be accessed directly. Novelty discs and CED-based games were produced whereby accessing the chapters in a specified order would string together a different story each time.
Disadvantages of SelectaVision
In comparison to VCR technology, CEDs suffered a few disadvantages. Most significantly, all CED players could only play one side of the disc at a time, which was limited to about 60-63 minutes of video. In order to play the entirety of a video recording longer than the maximum limit per side, the disc would have to be manually turned over. In order to flip a CED disc, the disc's sleeve would be inserted into the player to enclose and store the platter, and the sleeve would then be removed (with platter now inside), flipped over, and reinserted into the player (which would again extract the platter, now with the reverse side facing the stylus). Movies longer than 2 hours would require a second disc, which would need to be swapped in the player with the first disc after the 2 hour mark.
Repeated playing could lead to degradation of the video signal partially due to the wearout between the stylus and groove but primarily due to physical contact between the disc and the caddy during loading and unloading. Furthermore, any particulates that found their way into the player, the disc sleeve, or any indelicate use of the sleeve to insert or extract the platter from the player could result in scratches or other interference to the platter, which often resulted in rapid "skipping" of the audio/video signal, as well as serious signal degradation. Through ideal conditions and use, RCA suggested that a CED had a quality lifespan of about 500 plays, but this does not take into account the many factors that can impact disc life.
Available Video Programs
During the early months of the CED format, RCA handled the release and production and licensed films on the CED format from various studios and marketed the films under the RCA label. Eventually, CBS Video Enterprises (under the MGM/CBS and CBS/FOX Video labels), Disney, Paramount, MCA, MGM, Vestron Video and other labels began to produce CED discs under their own home video labels, and did so until the end of disc manufacturing in 1986.
Milestones
The first movie distributed in letterbox widescreen format, Amarcord, was released on SelectaVision in 1984.
The very first movie title on the format was "Race For Your Life, Charlie Brown", released in March 1981 with about 100 other titles.
The very last movie released on the format was "Jewel Of The Nile" on the CBS/FOX label, followed by "Memories Of Videodisc" which was available only to RCA factory workers.
See also
References
- Cowie, Jefferson R. Capital Moves: RCA's Seventy-Year Quest for Cheap Labor. Ithaca, N.Y.: Cornell University Press, 1999. ISBN 0801435250.
- Daynes, Rob and Beverly Butler. The VideoDisc Book: A Guide and Directory. New York: John Wiley and Sons, 1984. ISBN 0471803421.
- DeBloois, Michael L., ed. VideoDisc/Microcomputer Courseware Design. Englewood Cliffs, N.J.: Educational Technology Publications, 1982. ISBN 0877781834.
- Floyd, Steve, and Beth Floyd, eds. The Handbook of Interactive Video. White Plains, NY: Knowledge Industry Publications. 1982. ISBN 0867290196.
- Graham, Margaret B.W. RCA and the VideoDisc: The Business of Research. (Also as: The Business of Research: RCA and the VideoDisc.) Cambridge: Cambridge University Press, 1986. ISBN 0521322820, ISBN 0521368219.
- Haynes, George R. Opening Minds: The Evolution of Videodiscs & Interactive Learning. Dubuque, Iowa: Kendall/Hunt Publishing Co., 1989. ISBN 0840351917.
- Isailovi´c, Jordan. VideoDisc and Optical Memory Systems. Englewood Cliffs, N.J.: Prentice-Hall, 1985. ISBN 0139420533.
- Lardner, James. Fast Forward: Hollywood, the Japanese, and the VCR Wars. (Also as: Fast Forward: Hollywood, the Japanese, and the Onslaught of the VCR.) New York: W. W. Norton & Co Inc., 1987. ISBN 0393023893.
- Lenk, John D. Complete Guide to Laser/VideoDisc Player Troubleshooting and Repair. Englewood Cliffs, N.J.: Prentice-Hall, 1985. ISBN 0131608134.
- Schneider, Edward W., and Junius L. Brennion. The Instructional Media Library: VideoDiscs, (Volume 16). Englewood Cliffs, NJ: Educational Technology Publications. ISBN 0877781761. 1981.
- Sigel, Efrem, Mark Schubin and Paul F. Merrill. Video Discs: The Technology, the Applications and the Future. White Plains, N.Y. : Knowledge Industry Publications, 1980. ISBN 0914236563. ISBN 0442277849.
- Sobel, Robert. RCA. New York: Stein and Day/Publishers, 1986. ISBN 0812830849.
- Sonnenfeldt, Richard. Mehr als ein Leben (More than One Life). ?, 2003. ISBN 3502186804. (In German.)
- Journals:
- The Videodisc Monitor
- Videodisc News
- Videodisc/Optical Disk Magazine
- Video Computing