Video Recording

Abstract

Long before television became a household word, man endeavored to capture and record visual images. By the time the first electronic television was introduced at the 1939 World's Fair, both still and motion photography were well established in black and white and in color. Motion pictures, such as The Wizard of Oz , had full color images and complete audio sound tracks. An overview of video recording progress (both visual and aural signals) over almost 50 years since that 1939 World's Fair demonstration is provided. Throughout this article, the term video represents (except as specifically noted) a television signal consisting of program video, program audio (1, 2, or 4 channels) and a time‐code channel. For historical purposes a brief description of the kinescope process is included to provide a perspective on the more sophisticated magnetic and optical technologies which followed it and which dominate the video recording field. These technologies are described. Until the mid 1970s, commercial videotape recording focused on handling the composite video signal which contained all elements, luminance (brightness), chromanance (color information), and synchronization and timing pulses, within a single envelope. About the same time in 1978 as the consumer market saw the introduction of the digital laser disk, the same signal processing technologies were being applied to commercial recording, first by separately processing the luminance and chromanance signals in the analog domain and then, subsequently, by applying digital techniques to this process. Recording these two analog signal elements on separate video channels was termed component signal recording. It offered the advantage of reducing color artifacts during play‐back. For almost 20 years following its introduction in 1976, the VHS analog tape format remained preeminent in the consumer marketplace for video recording and playback. In 1995, barely 10 years after the highly successful introduction of the compact disk (CD) which provided digital, laser‐scanned playback, an analogous versatile digital disk format (DVD) became available for video recording. Like the laserdisk before it, the DVD, as currently available, is a play‐back‐only format. Even as DVD is being initially deployed in the marketplace, companies are investigating enhancement technologies to provide increased (double, quadruple, or higher) information storage capacity. One possible advance, derived linearly from present technology, seeks to replace the present binary digital encoding scheme with a multilevel scheme (nine states) which interprets the depth of the recorded pits to allow for coding beyond simply one or zero. A second potential avenue of increased storage capability focuses on substituting a blue light laser at a wavelength of 390 nm for the red light laser at 635 nm currently employed in DVD recording. Even as the aforementioned investigations of increased capacity are being pursued, attention is also being given to technologies which address the ability of the consumer to record at home, thereby creating a real replacement for the VCR. At least two main approaches are being followed at this time; optical phase change (OPC) and magneto‐optical (MO).