Laserdisc Guide, Meaning , Facts, Information and Description
Laserdisc, LD, or video laser disc was the first optical disc storage media, and an industry-wide term for consumer laser video. During its life, the format has also been known as LV (for LaserVision, actually a player brand by Philips). The players are also sometimes referred to as VDPs (Video Disc Players). Before release it was promoted under the name "Discovision".
LD was invented by David Paul Gregg (died 2003) in 1958, patented in 1961 and 1969, and first demonstrated by Philips and MCA in 1972. It was available on the market in 1978, or about the same time as the VCR and six years earlier than the CD.
There are more than 1 million players in home use in the US (compared to 85 million VCRs), and more than 4 million in Japan (ten percent of households there). LD has been largely replaced by DVD.
Video was stored on LD as an analog signal, while audio could be stored in a combination of several different formats. Like on a CD, the surface of the disc is an aluminium foil covered by pits and lands, but whereas on a audio CD (or DVD) the pits and lands will signify binary codes, on a LD the distance between two pits represents an analog sample level, the accuracy of which is dependent on the quality of the measurement.
NTSC LDs carried two analog audio tracks, plus two uncompressed CD-quality PCM digital audio tracks. PAL discs could carry one pair, either analog or digital. Some later LDs featured 5.1 channel Dolby Digital in place of the right analog audio track, and a small number included 5.1 channel DTS in place of the standard digital tracks.
Laserdiscs were recorded in one of two formats: CAV (constant angular velocity) or CLV (constant linear velocity). CAV discs were spun at a constant rotational speed during playback, with one video frame read per revolution, whereas CLV discs spun progressively slower as the disc was played from inside edge to outside edge.
CAV could hold up to 30 minutes of content per side, while CLV could hold twice that. The advantage of the CAV format was that its simpler playback method allowed "trick play" features such as freeze frame, slow motion, and reverse on all LD players, unlike CLV which only supported those features on high-end models with digital video buffers. The vast majority of titles were only available in CLV.
A very small number of LDs were mastered, for sale Japan or for promotion in the USA, using an anamorphic image technology, similar to the 16x9 anamorphic system used in DVDs. Among the very few films available in this format were Terminator 2, Basic Instinct, and The Fugitive. Displaying the squeezed image correctly required a widescreen television set, which at the time cost considerably more than a standard set, and as a result the format never caught on.
LD had a number of advantages over VHS. It featured a far sharper picture and level of sound quality, with the ability to deliver multiple audio channels, both analog and digital. This allowed "special editions" of movies with extras like director commentaries to be released. Access was random, meaning that one could go to any point on the disc very quickly (depending on the player and the disc, within a few seconds at the most). This instant seeking allowed a new breed of laserdisc-based video arcade games, beginning with Dragon's Lair, to be born. As LDs were read optically instead of magnetically, a properly-manufactured LD would theoretically last beyond one's lifetime, and as the discs had no moving parts, they were cheaper to manufacture. LDs would never "wear out" or lose quality with each playback as VHS tapes do.
The format was not without its disadvantages. The discs were 30cm (12 inch) across, and were both fragile and heavy. There was no way for home users to record to an LD. Depending on the format, each side of an LD could hold at most 30 or 60 minutes of content, and then the disc would have to be turned over. Most players did this automatically by rotating the optical pickup to the other side of the disc, but except in high-end models with a pre-read buffer, this was accompanied by a pause in the movie of around 10 seconds, and if the movie was longer than two hours, it eventually required putting in a second disc.
Many early laserdiscs were not manufactured properly. Sometimes a substandard adhesive was used to sandwich together the two sides of the disc, causing the disc to delaminate slightly and allowing oxygen to cause the metallic part of the discs to oxidize. This eventually destroyed the disc, a process known as "laser-rot" among LD enthusiasts. (Early CDs suffered similar problems, including a notorious batch of defective discs manufactured by Philips-DuPont Optical in Europe during the early 1990s.)
It is interesting to note that there are some advantages to the LD technology that result in some videophiles preferring LD to the more modern DVD. LDs offer analog video and sound. Many purists believe that analog media is capable of better resolution than digital counterparts such as CDs and DVDs. However, this is rarely achieved in practice. Only expertly mastered analog LDs may exhibit this superior quality and even then it requires very expensive high-end components (LD player, amplifier, television, etc.) in order to actually realize the benefits.
An advantage to the Laserdisc format over DVD is that video is not digitally-encoded and compressed, and therefore does not experience problems such as artifacting (most visible as blockiness during high motion sequences) or color banding (subtle visible lines in gradient areas, such as skies) that is inherent in the MPEG-2 encoding process as video is prepared for DVD. However, the meticulous (and expensive) frame-by-frame tuning of the lossy MPEG-2 encoding process generally employed on big-budget DVD releases effectively eliminates this, and an optional feature of the MPEG-2 compression standard allows much higher color resolution to eliminate the visible effect of color banding on some high-end home theatre equipment.
A disadvantage with the analog nature of Laserdiscs is that most players exhibit a slight but perceivable 30 Hz video flicker, and slight dust and wear on the hardware or disc can degrade video and audio over time. The DVD format, however, does not introduce any flicker, and the format's digital nature and sophisticated error-correction scheme can often produce spotless video/audio from a DVD, even with dust and scratches on the surface.
The format was not well-accepted outside of videophile circles in North America, but became more popular in Japan. Part of the reason was marketing. In North America the cost of the players and discs were kept far higher than VHS to make up for lack of demand. In Japan, LD was marketed like DVD (LD's replacement) was on its release: prices were kept low to ensure adoption, so in Japan an LD and a VHS tape were often identically priced. LD quickly became the dominant format of choice amongst Japanese collectors of anime, helping drive its acceptance.
The compact disc for audio was based on the laser disc technology. It may be that laser discs failed to reach mainstream acceptance because it was not possible to record onto them, whilst the competing video cassette recorder devices could record using tape cassettes. When they were first introduced, laser discs were believed to be disruptive technology, a promise they failed to fulfill. Compact discs and DVDs were to be disruptive instead.
Although LDs and their players have been completely supplanted by DVD and are no longer manufactured, many LDs were considered definitive releases of movies and are still highly coveted by movie enthusiasts. Boxed multi-disc LD editions of several films are prized as collector's items. There are many films that are only available on LD. As well, there are various films for which the LD is the most desirable release due to extra scenes, superior mastering, or lack of DVD availability. Thus, many LDs are still very much in demand.
Examples include the anime Five Star Stories, which was only released on LD despite its extreme popularity. Enthusiasts have been known to pay $700 or more for this LD. Likewise, the LD releases of the original Star Wars trilogy are in high demand among Star Wars fans because of all home video releases of the original versions of the films (which do not feature the editing and revisions found in the 1997 Special Editions or on the 2004 DVD release) they offer the highest video and audio quality.
There do exist "LD singles" which are 18 cm (7" aprox. , the same size as a 45-RPM record) across rather than the full 30 cm (12" aprox.) size. LD singles only contained a few minuites of video, enough for a music video or two. They are much rarer than the full-size LDs, especially in North America.
Some laser discs, called "picture discs", have artistic etching on one side of the disc to make the disc more visually attractive than the standard shiny silver surface. This etching might look like a movie character, logo, or other promotional material. Sometimes that side of the LD would be made with colored plastic rather than the clear material used for the data side. Picture disc LDs only had video material on one side as the "picture" side could not contain any data. Picture discs are rare in North America.
There existed another type of video media, CRV Disc, or "Component Recordable Video Disc". CRV discs resemble early PC CD-ROM caddies. The plastic housing of a CRV disc encloses an optical disc that resembles a standard LD. CRV discs existed as both pre-recorded releases and also as blank media that could be recorded, much like CD-R media. CRV was rarely used by the consumer due to the high cost of the equipment and media.History
Technical information
Laserdisc vs. VHS
Laserdisc vs. DVD
Success of the format
Laserdisc variations