Television Recording, Disk

Recording television signals onto a disk has been a goal of engineers since the inception of television broadcasting, and in recent decades the effort to perfect a disk television recorder has resulted in many competing systems. The disk phonograph was established as the medium for home audio listening by the time television was tentatively introduced in the 1920s and 1930s, so it was natural that experimenters imagined a disk-based accompaniment to future home television sets.

The earliest such system was probably that of Scottish inventor John Logie Baird. His ‘‘phonovision’’ disks, developed in 1926, recorded low-resolution television signals in a spiral groove on a phonograph disk. The output of the Baird camera, consisting of electrical pulses, was simply fed to an ordinary electromagnetic phonograph recording head, where the pulses modulated the movement of the cutting stylus.

Despite Baird’s progress, the introduction of television in the U.S. and Europe in the late 1930s would be based on the live broadcast of programs, instead of the distribution of recorded programs as in the case of the phonograph. The invention of a successful videotape recording system by the Ampex Corporation (U.S.) in the 1950s led to predictions of home video recorders, and these began to appear in the 1960s (see Television Recording, Tape).

The disk format was universally abandoned for commercial video recording, in part because the considerable bandwidth required for television signal recording demanded large areas of recording surface. This surface could be conveniently wound onto a spool in videotape systems, but would have required a very large disk to record even the 15- to 20-minute television shows of the day.

However, for certain types of short-duration recording, the fast access possible only with a disk led to special-purpose devices such as the Ampex ‘‘instant replay’’ disk recorder, introduced in 1966 and widely used in the broadcast of sporting events. The Ampex instant replay recorder utilized thirty concentric tracks on a large magnetizable disk, each track representing a single frame of television. Thirty in-line heads read these tracks and allowed the broadcast of slow motion, fast motion, or still images of up to thirty seconds of video.

Improvements in technology also led to the revival of video recording on phonographlike disk with the RCA Corporation’s (U.S.) ‘‘Selectavision’’ system introduced in early 1981. Using the so-called capacitance electronic disk, Selectavision employed a very fine groove and stylus to achieve a recording time of over 60 minutes per side on 12-inch (300-millimeters) diameter plastic disk. The walls of the exceedingly fine groove interacted with a special stylus to establish a varying capacitance between the stylus and the disk.

This varying capacitance contained the video information that was then processed and displayed on an ordinary television receiver. It was not possible for the consumer to make an original recording on the home players. Although considered a technical success, Selectavision was introduced at almost the same time as the soon-to-be popular Betamax and VHS home videotape systems. This competition, along with quality control problems and the lack of recording capability, caused RCA to discontinue Selectavision in 1986.

Meanwhile, various electronics manufacturers were experimenting with a video recording technology of a very different sort. These systems utilized the relatively new technologies of digital recording and optical reproduction by laser. Telefunken (Western Germany), RCA, MCA (U.S.), Thomson (France), Sony (Japan), and Phillips (Netherlands) all demonstrated such videodisc systems by 1982, with the first commercial product being the Philips/MCA ‘‘DiscoVision,’’ first sold in Atlanta, Georgia in December, 1978. The DiscoVision system recorded video information as pits on an aluminum-coated disk, and the player read the information using a reflected laser beam.

However, it was not a digital recording, but rather a frequency-modulated recording system reminiscent of earlier videotape recording technology. DiscoVision failed almost immediately, as did most of the competing systems of the 1980s. A similar Pioneer ‘‘Laserdisc’’ format on 12-inch disks was one of the one or two videodisc formats to survive into the 1990s, although it sold in numbers that were dwarfed by VHS sales.

While the compact audio disc, the audio-only variation of this technology developed by Sony and Philips, proved to be a commercial success, they also provided the basis for a new type of laser videodisc technology employing digital data recording. Pioneer Corporation was among the first to offer a digital videodisc, and employed the same sort of pulse code modulation circuitry already in use in long-distance telephony, data recording on magnetic tape, and other applications. The shift to digital video recording was spurred by the introduction of the personal computer, which utterly changed the context of videodisc development.

The CD-ROM, which became a popular way for software companies to deliver their products, was also once considered a competitor to VHS. While much smaller than the original digital videodiscs, it was in most other ways similar in operation. It was not common, however, to watch CD-ROM video presentations on home television sets, but rather on personal computers.

However, some record companies began to include short video clips on a CD-ROM disk in 1991, calling this product the ‘‘interactive’’ CD, or CD-I. CD-I players were intended to be connected to both the home audio system and to a television receiver. There were several other similar formats during the 1990s, such as the Eastman Kodak Company’s (U.S.) Photo CD, intended to compete with photographic prints for the storage of still images.

Video CD-ROMs achieved considerable commercial success, but did not have quite enough recording capacity to compete with videotape for the presentation of feature motion films, and at the peak of the CD-ROM’s popularity it did not seriously threaten the videotape market. It was, however, a more flexible video format than VHS, capable of conveniently storing moving and still images and providing multiple grades of quality to suit the user’s needs. Like all disk formats, the CD- ROM allows faster access to data located anywhere on the disk as compared to a linear tape format. Further, by 1996, a user-recordable disk called the CD-R was introduced, with a storage capacity comparable to a CD-ROM.

A refinement of the CD-ROM and CD-R is the Digital Video Disc (DVD, sometimes referred to as the Digital Versatile Disc) first offered in 1996. This format (which, like its predecessors, stores information as pits on a small laser-read disk) packs more information onto a CD-ROM size medium, and for the first time beats VHS tape in terms of both picture quality and recording time. Like the CD-ROM, it is equally applicable to both home video and personal computer applications.

The DVD began to sell in large enough numbers by 1999 to garner both larger amounts of shelf space in video stores as well as inclusion as original equipment in many new personal computer systems. A short time later, recordable DVD drives became available for use in conjunction with personal computers. While the DVD may itself be superceded, it seems likely that the place of the laser-read disk format in television recording is assured for the near future.