VHS

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This article is about the video format. For other uses, see VHS (disambiguation).
Video Home System
VHS Logo

Top view of VHS cassette with ruler for scale
Media type: video recording media
Encoding: FM on magnetic tape
Usage: video storage
Bottom view of VHS cassette with magnetic tape exposed
Bottom view of VHS cassette with magnetic tape exposed
Top view of VHS cassette with front casing removed
Top view of VHS cassette with front casing removed

The Video Home System, better known by its abbreviation VHS is a recording and playing standard for analog video cassette recorders (VCRs), developed by Victor Company of Japan, Limited (JVC) and launched in September 1976.[1]

By the 1990s, VHS became a standard format for consumer recording and viewing, after competing in a fierce format war with Sony Corporation's Betamax and, to a lesser extent, Philips' Video 2000. VHS initially offered a longer playing time than the Betamax system, and it also had the advantage of a far less complex tape transport mechanism. Although VHS and Betamax were competing formats, several of VHS' critical technologies are licensed from Sony. Early VHS machines could rewind and fast forward the tape considerably faster than a Betamax VCR since they unthreaded the tape from the playback heads before commencing any high-speed winding. Most newer VHS machines do not perform this unthreading step, as head-tape contact is no longer an impediment to fast winding, due to improved engineering.

The week of 15 June 2003 marked the first time the DVD format (which was launched in the late 1990s) became more popular than VHS in the USA. Although still popular for home recording, the VHS tape has largely been replaced by DVD for pre-recorded home video content.

As of July 2006, most major film studios have stopped releasing new movie titles in VHS format, opting for DVD-only releases. VHS prerecorded cassettes, however, are still popular with many collectors, mainly because there are thousands of titles that are still unavailable on DVD or other newer formats.

Contents

[edit] Technical details

The VHS cassette is about 7 1/4" wide x 4" deep x 1" thick plastic clamshell held together with 5 philips head screws. The flip-up cover that protects the tape has a built-in latch with a push-in toggle on the right side, as seen in the Bottom View. The VHS cassette also includes an anti-despooling mechanism as seen in the Top View, several plastic parts near front label end of the cassette between the two spools. The spool brakes are released by a push-in lever within a 1/4" hole accessed from the bottom of the cassette, about 3/4" in from the edge label. There is a clear tape leader at both ends of the tape to provide an optical auto-stop for the VCR transport mechanism.

The recording medium is a ½ inch (12.7 mm) wide magnetic tape wound between two spools, allowing it to be slowly passed over the various playback and recording heads of the video cassette recorder. The tape speed is 3.335 cm/s for NTSC, 2.339 cm/s for PAL. A cassette holds a maximum of about 430 m of tape at the lowest acceptable tape thickness, giving a maximum playing time of about 3.5 hours for NTSC and 5 hours for PAL at "standard" (SP) quality. Most cassettes have lower recording times because they use thicker tape, which helps avoid jams; careful users generally avoid the thinnest tapes. More recent machines usually allow the selection of longer recording times by lowering the tape speed: LP mode (for PAL and some NTSC machines) halves the tape speed and doubles the recording time, while EP mode (for NTSC and some newer PAL machines, aka SLP mode) drops the tape speed to one-third, for triple the recording time. Of course, these speed reductions cause corresponding reductions in video quality; also, tapes recorded at the lower speed often exhibit poor playback performance on recorders other than the one they were produced on. Because of this, commercial prerecorded tapes were almost always recorded in SP mode. The only exceptions were "discount" tapes, usually containing children's cartoons or older shows, usually recorded at SLP speed but sometimes including Hi-Fi audio to help enhance sound quality. An unofficial LP mode with half the standard speed exists on some NTSC machines, but is not part of the VHS standard.

VHS M-loading system
VHS M-loading system

As with almost all cassette-based videotape systems, VHS machines pull the tape from the cassette shell and wrap it around the head drum. VHS machines, in contrast to Betamax and Beta's predecessor U-matic, use an M-loading system, also known as M-lacing, where the tape is drawn out by two threading posts and wrapped around the head drum (and other tape transport components) in a shape roughly approximating the letter M.

The interior of a modern VHS VCR showing the drum, tape, and cassette
The interior of a modern VHS VCR showing the drum, tape, and cassette

VHS tapes have approximately 3 MHz of video bandwidth, which is achieved at a relatively low tape speed by the use of helical scan recording of a frequency modulated luminance (black and white) signal, to which a frequency-reduced "color under" chroma (hue and saturation) signal is added. In the original VHS format, audio was recorded unmodulated in a single (binaural) linear track at the upper edge of the tape, which was limited in frequency response by the tape speed (about 100 Hz to 8 kHz with 42 dB signal-to-noise ratio at SP). The vast majority of home recorders only supported monaural for the linear audio track, even though studio film releases began to emerge in stereo from 1982. High-end consumer recorders with linear stereo playback also became available around this time, and these machines often offered other editing facilities. Around 1985, HiFi VCRs emerged, adding higher-quality stereo audio tracks (20 Hz to 20 kHz with more than 70 dB S/N ratio at SP) which are read and written by heads located on the same spinning drum that carries the video heads, frequency modulated to the unused frequency range in between the chroma and luma signals. These audio tracks take advantage of depth multiplexing: since they use lower frequencies than the video, their magnetization signals penetrate deeper into the tape. When the video signal is written by the following video head, it erases and overwrites the audio signal at the surface of the tape, but leaves the deeper portion of the signal undisturbed. The excellent sound quality of HiFi VHS has gained it some popularity as an audio format in certain applications; in particular, ordinary home HiFi VCRs are sometimes used by home recording enthusiasts as a handy and inexpensive medium for making high-quality stereo mixdowns and master recordings from multitrack audio tape. As HiFi audio became the norm, manufacturers gradually dropped the more expensive, and inferior, linear stereo facility and reverted to mono for the linear track.

Of course, for backward compatibility, HiFi VCRs still write the linear audio track during recording and can automatically read it during playback if the HiFi audio is not present, or badly degraded, but very few machines support both HiFi audio and linear stereo audio.

Because VHS is an analog system, VHS tapes represents video as a continuous stream of colour, in a manner similar to analog TV broadcasts, while digital video are displayed on a television set are a rectangle of discrete pixels. The waveform of a VHS video signal can change frequency about 240 times within the width of a scanline[1], and contains up to 486 visible scanlines in NTSC, or 576 lines in PAL. Because television sets are more than 240 pixels wide, the video stream is stretched across the width of the television. The frequency modulation of the luminance signal makes higher resolutions impossible within the VHS standard, no matter how advanced the recorder's technology. The signal-to-noise ratio of the image signal is around 43 dB.

A peculiarity of VHS machines is a jittering dot at the bottom of the screen, corresponding to the point at which the VCR's electronics switch from one head to the other as the rotating head drum completes reading a stripe of video. The "switching point" used to be obscured in older TV sets which tended to overscan more than newer sets.

Some higher-end VHS and S-VHS VCRs once offered "audio dubbing" and "video dubbing" functions. These would move the tape past the heads and keep the video unchanged while recording new linear audio or keep the linear audio unchanged while recording new video, respectively. This was useful, for example, for laying a song over a previously edited-together montage of short video clips that were the same total duration as that song. Without the dubbing features, this task would have required the tape to be copied to another tape which would cause generational loss. Due to the different ways in which linear and HiFi audio are recorded, these kinds of dubbing were not possible with the HiFi tracks. Another high-end feature was manual audio level control, which made the VHS HiFi format much more useful for high-quality audio-only recording purposes as discussed above. Some higher end machines, particularly S-VHS VCRs made by JVC, still offer audio and video dub features, though most modern VCRs do not.

Another linear control track, at the tape's lower edge, holds pulses that mark the beginning of every frame of video; these are used to fine-tune the tape speed during playback and to get the rotating heads exactly on their helical tracks rather than having them end up somewhere between two adjacent tracks (a feature called tracking). Since good tracking depends on the exact distance between the rotating drum and the fixed control/audio head reading the linear tracks, which usually varies by a couple of micrometers between machines due to manufacturing tolerances, most VCRs offer tracking adjustment, either manual or automatic, to correct such mismatches.

The control can additionally hold index marks. These are normally written at the beginning of each recording session, and can be found using the VCR's index search function: this will fast-wind forward or backward to the nth specified index mark, and resume playback from there. There was a time when higher-end VCRs provided functions for manually removing and adding these index marks — so that, for example, they coincide with the actual start of the program — but this feature has become hard to find in recent models.

[edit] Variations

Bottom and top view of VHS-C compact video cassette
Bottom and top view of VHS-C compact video cassette
Example of a VHS-C adapter
Example of a VHS-C adapter

Several improved versions of VHS exist, most notably Super-VHS (S-VHS), an analog video standard with improved video bandwidth, and Data-VHS (D-VHS), which records high definition video onto a VHS form factor tape.

Devices have also been invented which directly connect a personal computer to VHS tape recorders for use as a data backup device. Most notable of these devices was ArVid, widely used in Russia and CIS states.

W-VHS caters for analog high definition video.

Another variant is VHS-Compact (VHS-C), used in some camcorders, primarily small form factor low-end consumer units. Since VHS-C tapes are based on the same magnetic tape as full size tapes, they can be played back in standard VHS players using a mechanical adapter, without the need of any kind of signal conversion. The magnetic tape on VHS-C cassettes is wound on one main spool and uses a gear wheel to advance the tape; the wheel and spool can also be moved by hand. This development hampered the sales of the Betamax system somewhat, because the Betamax cassette geometry prevented a similar development. As of 2006, there are no full-sized VHS camcorders still on the market; the rapidly dwindling VHS camcorder market consists entirely of VHS-C units.

There is also a JVC-designed component digital professional production format known as Digital-S, or officially under the name D9, that uses a VHS form factor tape and essentially the same mechanical tape handling techniques as an S-VHS recorder. This format is the least expensive format to support a pre-read edit. This format is most notably used by Fox for some of its cable networks.

[edit] Signal standards

VHS can record and play back all varieties of analog television signals in existence at the time VHS was devised. However, a machine must be designed to record a given standard. Typically, a VHS machine can only handle signals of the country it was sold in. The following signal varieties exist in conventional VHS:

  • PAL/625/25 (most of Western Europe, Australia, many parts of Asia (such as China and India), some parts of South America (such as Argentina and Uruguay) and Africa)
  • SECAM/625/25 (SECAM, French variety)
  • MESECAM/625/25 (most other SECAM countries, notably the former Soviet Union and Middle East)
  • NTSC/525/30 (Most parts of North and South America, Japan, South Korea)
  • PAL/525/30 (i.e. PAL-M, Brazil)

Since the 1990s, dual- and multi-standard VHS machines have become more and more common. These can handle VHS tapes of more than one standard. E.g. regular VHS machines sold in Australia and Europe nowadays can typically handle PAL, MESECAM for record and playback, plus NTSC for playback only. Dedicated multistandard machines can usually handle all standards listed, some high end model can even convert a tape from one standard to another by using a built-in standards converter.

S-VHS only exists in PAL/625/25 and NTSC/525/30. S-VHS machines sold in SECAM markets record internally in PAL, and convert to/from SECAM during record/playback, respectively. Likewise, S-VHS machines for the Brazilian market record in NTSC and convert to/from PAL-M.

Virtually all currently available VHS decks, even those offered as part of a VCR/DVD combination unit, output only composite video.

A small number of VHS decks are able to decode closed captions on pre-recorded video cassettes. A smaller number still are able, additionally, to record subtitles transmitted with world standard teletext signals (on pre-digital services), simultaneously with the associated programme.

[edit] Tape lengths

Both NTSC and PAL/SECAM VHS cassettes are physically identical (although the signals recorded on the tape are incompatible.) However, as tape speeds differ between NTSC and PAL/SECAM, the playing time for any given cassette will vary accordingly between the systems.

In order to avoid confusion, manufacturers indicate the playing time in minutes that can be expected for the market the tape is sold in:

  • T-XXX indicates playing time for NTSC or PAL-M in SP speed.
  • E-XXX indicates playing time for PAL or SECAM in SP speed.

It is perfectly possible to record and play back a blank T-XXX tape in a PAL machine or a blank E-XXX tape in an NTSC machine, but the resulting playing time will be different from that indicated. It can easily be derived by multiplying with 3/2 or 2/3, respectively.

For example, a T-120 tape runs for 120 minutes in NTSC-SP, but 180 minutes in PAL-SP. Conversely, an E-300 tape runs for 300 minutes in PAL-SP, but 200 minutes in NTSC-SP.

Common VHS Tape Lengths
Tape Label Tape Length Rec. Time (NTSC) Rec. Time (PAL)
SP EP/SLP SP LP
T-120 812 ft (247.5 m) 2 h 6 h 2 h 49 min 5 h 38 min
T-160 1075 ft (327.7 m) 2 h 40 min 8 h 3 h 43 min 7 h 26 min
T-180 1210 ft (368.8 m) 3 h 9 h 4 h 13 min 8 h 27 min
Tape Label Tape Length Rec. Time (PAL) Rec. Time (NTSC)
SP LP SP EP/SLP
E-120 570 ft (173.7 m) 2 h 4 h 1 h 26 min 4 h 18 min
E-180 851 ft (259.4 m) 3 h 6 h 2 h 9 min 6 h 27 min
E-240 1142 ft (348.1 m) 4 h 8 h 2 h 53 min 8 h 39 min

[edit] VHS vs. Betamax

Main article: Videotape format war
Size comparison between a Betamax cassette and a VHS cassette.
Size comparison between a Betamax cassette and a VHS cassette.

As mentioned, VHS was the winner of a protracted and somewhat bitter format war during the early 1980s against Sony's Betamax format. Since Betamax was widely perceived at the time as the better format, it is often stated that VHS' eventual victory was proof that marketing can win over technical excellence. In fact, the root causes of VHS' victory are somewhat more complex. Betamax held an early lead in the format war, offering some technical advantages. By 1980, VHS was gaining marketshare due to its longer tape time (3 hours maximum, compared to just 60 minutes for Betamax in USA) and JVC's less strict licensing program. The longer tape time is sometimes cited as the defining factor in the format war, allowing consumers to record entire programs unattended (recording time between VHS and Betamax were similar in areas where VHS entered the market several years after introduction, such as the UK in 1978.) Sony ultimately conceded the fight in the late 1980s, bringing out a line of VHS VCRs of its own.

The format war and the "marketing over technology" claims have taken on a life of their own, and continue to be used as analogies in battles within the computer industry, including Apple vs. IBM, Macintosh vs. PC, Microsoft Internet Explorer vs. Netscape/Mozilla Firefox, and HD DVD vs. Blu-ray Disc.

Other formats such as 8 mm video cassettes and MiniDV have emerged since the post-battle era, but these formats are by no means in complete competition with VHS. As these cassettes and their supporting hardware are much more compact in design than VHS -- and therefore more expensive -- they are much more suited to portable applications such as camcorders. 8 mm tapes, introduced in the early 1980s, succeeded as a format for camcorders (both in the consumer, and to an extent, professional market), as VHS and Betamax camcorders were unsuitably large and heavy in comparison. MiniDV has largely replaced 8 mm tapes as the de facto camcorder standard in more recent years as it is smaller still (some MiniDV camcorders being no larger than one's hand). In addition, MiniDV offers superior audiovisual quality, and the storage of data in digital format on tape makes for improved transfer and editing. Though Digital8 offers identical tape recording quality, few are now sold and fewer still can play analog 8 mm tape, which was the original advantage of the format for those upgrading from analog 8 mm or later analog Hi8 formats. Some users of Digital8 have pointed out that their format offers a slightly more robust physical package, as the digital data is recorded over a larger area of magnetic tape. This is has not been any advantage to the format however.

Both VHS and Betamax manufacturers created professional video formats built around the same cassette shells. The professional derivatives of VHS were M and then MII whereas the professional derivative of Betamax was Betacam which has gone on to spawn digital variants. In a complete reversal of the domestic VHS-Betamax battle, in the professional arena the Beta format has been hugely successful, and the VHS derived formats became obsolete. Occasionally this causes some confusion in that people believe that Betamax is a professional studio format, but in fact it is the superficially very similar Betacam format they are thinking of.

[edit] Decline of VHS

In recent years, non-tape based technologies have appeared in the home recording market. The movement is to replace tape with more recent technologies, such as optical discs, hard disk drives and flash-based storage systems. Altogether, these technologies are shrinking VHS' marketshare. The March 1997 introduction of the DVD format to American consumers was perhaps the greatest blow to the dominance of VHS.[2]

Signs of VHS' decline come from two directions. First, electronic equipment manufacturers are downsizing their VHS recorder lines. Both department and electronic "boutique" stores are also cutting down on the variety of VHS recorders they carry in-stock — especially the higher-end systems such as S-VHS recorders.

Second, video content in VHS format is also slowly disappearing. The popularity of VHS in both for-sale and rental stores has fallen. Most retail stores have stopped selling new VHS movies alongside DVD versions. On November 27, 2006, the Motion Picture Association of America (MPAA) announced that commercial films will no longer be released on VHS.[citation needed] Last MPAA movie released on VHS was Borat: Cultural Learnings of America for Make Benefit Glorious Nation of Kazakhstan

Although VHS is slowly disappearing, this dilemma does bring along with it opportunities, such as media conversion services, dual-deck and DVD/VCR combination systems, and even a lucrative re-sell market on auction and second-hand equipment sites. Consumers still retain the technology as well. The Washington Post has noted that as of 2005, 94.5 million Americans still owned VHS format VCRs.[3]

[edit] Optical disc-based technologies

The Digital Versatile Disc (DVD) format was introduced first, in 1996, in Japan, to the United States in March of 1997, mid-late 1998 in Europe and early 1999 in Australia.

Despite DVD's better quality, VHS is still widely used in home recording of television programs, due to the large installed base and the lower cost of VHS recorders and tape. The commercial success of DVD recording and re-writing has been hindered by a number of factors including:

  • A reputation for being temperamental and occasionally unreliable, as well as the risk caused by scratches.
  • Shorter recording time: 2 hours on a single-layer disc (up to 4 or 6 hours with higher compression) versus 3 (NTSC) or 5 (PAL/SECAM) hours (up to 15 hours using PAL EP) on a VHS tape. Dual layer recorders and media have not yet become commonplace.
  • Dual layer DVD discs are still quite expensive

[edit] High-capacity digital recording technologies

High-capacity digital recording systems are also gaining in popularity with home users. These types of systems come in several form factors:

Hard disk-based systems include TiVo as well as other digital video recorder (DVR) offerings. These types of systems provide users with virtually a no-maintenance solution for capturing video content. VHS and other cartridge solutions require physical handling of the media, as well as upkeep duties such as cleaning of the heads. Unlike both cartridge-based and optical disc-based systems, hard disk-based systems allow for many hours of recording without physical maintenance. For example, a 120 GB system recording at an extended recording rate (XP) of 9,800 bps MPEG-2 can record over 25 hours of video content. Just like VHS, the latest optical disc technologies must still rely on tangibles, such as blank discs

PC-based media centers are also becoming popular in homes. PCs can serve the same features as a DVR set-top box, but also add a usable operating environment for other tasks such as electronic mail and surfing the Internet. A media center may be the better solution for the technical-savvy consumer who is looking for a system he can regularly upgrade, such as disk capacity and software.

[edit] VHS portrayed in entertainment

  • Toei produced a motion picture called Hi wa Mata Noboru (2002), starring Toshiyuki Nishida. Toshiyuki plays the role of Shizuo Kagaya, the head of the video department at Victor. In the process of developing a home VCR, he basically invents VHS. Although the movie is based on a true story, it was produced purely for entertainment and not as a documentary, which explains some of the over-dramatizations of its characters and events. Several important events are covered, such as the unification of VCR standards by Japan's Ministry of Trade, who favored Sony's Betamax format, and the importance in Victor bringing Matsushita on-board as a partner to build VHS units.

[edit] Trivia

  • The font used in the VHS logo is called "Lee". It was created in 1972 by Leo Weisz for Visual Graphics Corporation (VGC).
  • In the late 1980s, Tandy Radio Shack marketed a computer data backup device based on recording to VHS tape. Other, similar devices have been created and marketed since for various platforms.
  • The final major motion picture released on VHS was David Cronenberg's A History of Violence.[2]
  • Occasionally, some people refer to VHS as Vertical Helical Scan, which is the recording system.[citation needed]

[edit] References

  1. ^ "IEEE History Center: Development of VHS" accessed December 28, 2006, cites the original name as "Video Home System", from an article by Yuma Shiraishi, one of its inventors
  2. ^ Washington Post
  3. ^ Washington Post

[edit] External links

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