Video Home System, better known by its abbreviation VHS, is a video tape recording standard developed during the 1970s. It was released to the public during the latter half of the decade. During the late part of the 1970s and the early 1980s it formed one-half of the VHS vs Betamax war, which VHS would eventually go on to win. VHS' properties include longer playing time, faster rewinding and fast-forwarding, and a less complex tape transport mechanism. The open standard used for VHS technology allowed mass production without licensing costs. VHS would eventually come out as the winning video tape format, surpassing other home tape formats by the 1990s.

In later years, optical disc formats began to offer better quality than video tape, and took over in film studios, then retailers, and finally video rental stores. By 2006, the United States had stopped releasing new movie titles in VHS format, opting for others such as DVD and Blu-ray. On December 31, 2008, the last major United States supplier of pre-recorded VHS tapes, Distribution Video Audio Inc. of Palm Harbor, Florida, shipped its final truckload.

Technical details

Video recording

A VHS 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. Other speeds include LP and EP/SLP which double and triple the recording time, for NTSC regions. These speed reductions cause a slight reduction in video quality (from 250 lines to 230 analog lines horizontal); 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.

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, with a down-converted "color under" chroma (color) signal recorded directly at the baseband. Because VHS is an analog system, VHS tapes represent video as a continuous stream of waves, in a manner similar to analog TV broadcasts. The waveform per scan-line can reach about 160 waves at max, and contains 525 scanlines from top of the screen to bottom of the screen in NTSC (480 visible). PAL variants have 625 scanlines (576 visible). In modern-day digital terminology, VHS is roughly equivalent to 333x480 pixels.

JVC would counter 1985's SuperBeta with VHS HQ, or High Quality. The frequency modulation of the VHS luminance signal is limited to 3 megahertz which makes higher resolutions impossible, but an HQ branded deck includes luminance noise reduction, chroma noise reduction, white clip extension, and improved sharpness circuitry. The effect was to increase the apparent horizontal resolution of a VHS recording from 240 to 250 analog (equivalent to 333 pixels from left-to-right, in digital terminology). The major VHS OEM resisted HQ due to cost concerns, eventually resulting in JVC reducing the requirements for the HQ brand to white clip extension plus one other improvement.

In 1987 JVC introduced the new format called Super VHS which extended the bandwidth to over 5 megahertz, yielding 420 analog horizontal (560 pixels left-to-right).

Audio recording

In the original VHS format, audio was recorded as baseband in a single linear track, at the upper edge of the tape, similar to how an audio compact cassette operates. The recorded frequency range was dependent on the movement of the tape past the audio head, which for the VHS SP mode, resulted in a mediocre frequency response of roughly 100 Hz to 10 kHz. The signal-to-noise ratio was an acceptable 42 dB. Both parameters degraded significantly with VHS's longer play modes, with EP frequency response peaking at 4 kHz.

More expensive decks offered stereo audio recording and playback. Linear stereo, as it was called, fit two independent channels in the same space as the original mono audiotrack. While this approach preserved acceptable backward compatibility with monoaural audio heads, the splitting of the audio track degraded the signal's SNR to the point that audible tape hiss was objectionable at normal listening volume. To counteract tape hiss, decks applied Dolby B noise reduction for recording and playback. Dolby B dynamically boosts the mid-frequency band of the audio program on the recorded medium, improving its signal strength relative to the tape's background noise floor, then attenuates the mid-band during playback. Dolby B is not a transparent process, and Dolby-encoded program material will exhibit an unnatural mid-range emphasis when played on non-Dolby capable VCRs.

High-end consumer recorders took advantage of the linear nature of the audio track, as the audio track could be erased and recorded without disturbing the video portion of the recorded signal. Hence, "audio dubbing" and "video dubbing", where either the audio or video are re-recorded on tape (without disturbing the other), were supported features on prosumer editing-decks. Without dubbing capability, an audio or video edit could not be done in-place on master cassette, and requires the editing output be captured to another tape, incurring generational loss.

Studio film releases began to emerge with linear stereo audiotracks in 1982. From that point onward nearly every home video releases by Hollywood featured a Dolby-encoded linear stereo audiotrack. However, linear stereo was never popular with equipment makers or consumers.

Around 1985, JVC added Hi-Fi audio to VHS (in response to Betamax's introduction of Beta Hi-Fi.) Both VHS Hi-Fi and Betamax Hi-Fi delivered flat full-range frequency response (20 Hz to 20 kHz), excellent 70 dB signal-to-noise ratio (in consumer space, second only to the compact disc), dynamic range of 90 dB, and studio-grade channel separation (more than 70dB). VHS Hi-Fi audio is achieved by using audio frequency modulation (AFM), recording each of the 2 stereo channels (L, R) on a frequency-modulated carrier and embedding the modulated audio signal pair into the video signal. To avoid crosstalk and interference from the primary video carrier, VHS's implementation of AFM relied on a form of magnetic recording called depth multiplexing. The modulated audio carrier pair was placed under the luminance carrier (below 1.6 MHz), and recorded first. Subsequently, the video head erases and re-records the video signal over the same tape surface, but video signal's higher center frequency results in a shallower magnetization of the tape, allowing both the video and residual AFM audio signal to coexist on tape. (PAL versions of Beta Hi-Fi use this same technique). During playback, VHS Hi-Fi recovers the depth-recorded AFM signal by subtracting the audio head's signal (which contains the AFM signal contaminated by a weak image of the video signal) from the video head's signal (which contains only the video signal), then demodulates the left and right audio channels from their respective frequency carriers. The end result of the complex process was audio of outstanding fidelity, which was uniformly solid across all tape-speeds (EP or SP.) Since JVC had gone through the complexity of ensuring Hi-Fi's backward compatibility with non-Hi-Fi VCRs, virtually all studio home video releases contained Hi-Fi audiotracks (in addition to the linear audio track). Under normal circumstances, all Hi-Fi VHS VCRs will record Hi-Fi and linear audio simultaneously to ensure compatibility with VCRs without Hi-Fi playback, though only early, high-end Hi-Fi machines provided linear stereo compatibility.

The sound quality of Hi-Fi VHS stereo is comparable to the quality of CD audio, particularly when recordings were made on high-end or professional VHS machines that have a manual audio recording level control. This high quality compared to other consumer audio recording formats such as compact cassette attracted the attention of amateur and hobbyist recording artists. Home recording enthusiasts occasionally recorded high quality stereo mixdowns and master recordings from multitrack audio tape onto consumer-level Hi-Fi VCRs. However, because the VHS Hi-Fi recording process is intertwined with the VCR's video-recording function, advanced editing functions such as audio-only or video-only dubbing are impossible. Some VHS decks also had a "simulcast" switch, allowing users to record an external audio input along with off-air pictures. Some televised concerts offered a stereo simulcast soundtrack on FM radio and as such, events like Live Aid were recorded by thousands of people with a full stereo soundtrack despite the fact that stereo TV broadcasts were some years off (especially in regions that adopted NICAM).

The considerable complexity and additional hardware limited VHS Hi-Fi to high-end decks for many years. While linear stereo all but disappeared from home VHS decks, it was not until the 1990s that Hi-Fi became a more common feature on VHS decks. Even then, most customers were unaware of its significance and merely enjoyed the better audio performance of the newer decks.

Cassette and tape design

The VHS cassette is a 187 mm wide, 103 mm deep, 25 mm thick (7⅜" × 4" × 1") plastic clamshell held together with five Phillips head screws. The flip-up cover that protects the tape has a built-in latch with a push-in toggle on the right side (see bottom view image). 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 6.35 mm (1/4") hole accessed from the bottom of the cassette, about 19.05 mm (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. A light source is inserted into the cassette (through the circular hole in the center of the underside) when loaded in the VCR, and two photodiodes are located to the left and right sides of where the tape exits the cassette - when the clear tape reaches one of these, enough light will pass through the tape to the photodiode to trigger the stop function, or in more sophisticated machines it will start rewinding the cassette when the trailing end is detected. Early VCRs used an incandescent bulb as the light source, which can fail and may cause the VCR to erroneously think that a cassette is loaded when empty, or will detect the blown bulb and stop functioning completely. Later designs use an infrared LED which has a much longer lifetime.

The recording medium is a 12.7 mm (½ inch) 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. 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 or omega wrap, where the tape is drawn out by two threading posts and wrapped around more than 180 degrees of the head drum (and also other tape transport components) in a shape roughly approximating the letter M.

Tracking adjustment and index marking

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.

By the late 1990s, some high-end VCRs offered more sophisticated indexing. For example, Panasonic's Tape Library system assigned an ID number to each cassette, and logged recording information (channel, date, time and optional program title entered by the user) both on the cassette and in the VCR's memory for up to 900 recordings (600 with titles).

Variations

Super-VHS / Digital-VHS (high-definition) / ADAT

Several improved versions of VHS exist, most notably Super-VHS , an analog video standard with improved video bandwidth. S-VHS improved the luminance resolution to 400 horizontal per picture height (versus 250 for VHS/Beta and 500 for DVD). The audio-system (both linear and AFM) is the same. S-VHS made little impact on the home market, but gained dominance in the camcorder market due to its superior picture quality.

The ADAT format provides the ability to record multitrack digital audio using S-VHS media.

The other improved standard, called Digital-VHS , records digital high definition video onto a VHS form factor tape. D-VHS can record up to 4 hours of ATSC Digital Television in 720p or 1080i formats using the fastest record mode (equivalent to VHS-SP), and up to 40 hours of standard definition video at slower speeds.

VHS-C / Super VHS-C

Another variant is VHS-Compact , originally developed for portable VCRs in 1982, but ultimately finding success in palm-sized camcorders. 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 longest tape available holds 40 minutes in SP mode and 120 minutes in EP mode.

Super VHS or S-VHS was developed by JVC in 1987. S-VHS provided an improved luminance and chrominance quality, yet S-VHS recorders were compatible with VHS tapes.

Sony Betamax was unable to shrink that form any further, so instead they developed Video8/Hi8 which was in direct competition with the VHS-C/S-VHS-C format throughout the 80s, 90s, and 2000s. Ultimately neither format "won" and both continue to be sold in the low-end market (examples: JVC SXM38 and Sony TRV138). Super VHS-C camera recordings can be played back in standard VHS VCRs with SVHS-ET technology.

Use as PC backup devices

There is some controversy over whether you could use a domestic VCR to be able to record PC contents on it. However there are some devices which have allowed personal computer to hook up a VHS tape recorders for use as a data backup device. Most notable of these devices was ArVid, widely used in Russia and CIS states. Also available in the United States were similar systems manufactured by Corvus, Videotrax, and Alpha Microsystems. Also available was Backer from Danmere Ltd. of England.

HP also developed a backup system that used VHS tapes known internally as Hero, storing up to 5 GB per tape. It was cancelled in 1987 as it was quickly overtaken by DAT tapes which became available at similar storage capacity and smaller physical size.

W-VHS

W-VHS allowed recording of MUSE Hi-Vision analog high definition television, which was broadcast in Japan from 1989 until 2007.

D9

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.

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:

• 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 Americas, Japan, South Korea)
• PAL/525/30 (i.e., PAL-M, Brazil)
• PAL/576/25 (most of Western Europe, Australia, many parts of Asia such as China and India, some parts of South America such as Argentina, Uruguay and the Falklands, and Africa)

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. For example, 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.

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 program.

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. 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. SP is Standard Play and LP is Long Play at 1/2 speed for both NTSC and PAL regions. EP/SLP designates Extended Play/Super Long Play at 1/3rd speed for NTSC regions.

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

Common Tape Lengths in minutes (hours)

Tape Label	Tape Length		Rec. Time (NTSC)			Rec. Time (PAL)
	m	ft	SP	LP	EP/SLP	SP	LP
T-120	247.5	812	120 min (2 h)	240 min (4h)	360 min (6h)	169 min (2:49 h)	338 min (5:38 h)
T-180	368.8	1210	180 min (3 h)	360 min (6 h)	540 min (9 h)	253 min (4:13 h)	507 min (8:27 h)
T-210 (rare)	433.1	1421	210 min (3:30 h)	420 min (7 h)	630 min (10:30 h)	294 min (4:56 h)	592 min (9:52 h)
DF480 (T-240 equiv)	495	1624	240 min (4 h)	480 min (8 h)	720 min (12 h)	340 min (5:40 h)	680 min (11:20 h)
E-120	173.7	570	83 min (1:26 h)	172 min (2:52 h)	258 min (4:18 h)	120 min (2 h)	240 min (4 h)
E-180	259.4	851	129 min (2:09 h)	258 min (4:18 h)	387 min (6:27 h)	180 min (3 h)	360 min (6 h)
E-240	348.1	1142	173 min (2:53 h)	346 min (5:46 h)	519 min (8:39 h)	240 min (4 h)	480 min (8 h)

Uses in marketing

Although VHS was a popular delivery format for long-play content, VHS was also used to deliver short-play content, such as music videos, in-store videos and tutorials.

VHS single

VHS single, also known as videotape single or Video 45s (a play on the term "45" when used to describe vinyl records), is a music single, using a standard-sized VHS cartridge. The format has existed since the early 1980s. In 1983, British synthpop band The Human League released the UKs first commercial video single called "The Human League Video Single". It wasn't a huge commercial success due to the high retail price of £10.99, compared to £1.99 for a vinyl single.

The VHS single format gained higher levels of mainstream popularity when Madonna released "Justify My Love" as a video single in 1990 following the blacklisting of the video by MTV. U2 also released "Numb", the lead single from their 1993 album Zooropa as a video single.

Despite the success of these releases, the video single struggled as its releases were relatively periodical, the technology slowly being superseded first by music CDs with computer-accessible video files, then, by the early 2000s, by both DVD singles and CD+DVD releases.

Other uses

VHS was also commonly included in various products and services - including exercise equipment, kitchen appliances, and even computer software. Corporations used the VHS format to deliver addresses made by company executives to regional offices. Manufacturers would send out VHS tapes to its service centers, to demonstrate how to repair a new product. And, retail stores would play VHS tapes demonstrating a product on a television set, requiring a VCR that supported encore function replay or auto rewind play.

VHS vs. Betamax

VHS was the winner of a protracted and somewhat bitter format war during the late 1970s and early 1980s against Sony's Betamax format.

Betamax was widely perceived at the time as the better format, as it offered a slightly higher vertical resolution (250 lines vs. 240 lines in PAL & NTSC), lower video noise, and less luma-chroma crosstalk than VHS, and was marketed as providing pictures superior to VHS's, however the introduction of B-II speed (2-hour mode) to compete with VHS's 2-hour Standard Play mode, reduced Betamax's vertical resolution to 240 lines. The extension of VHS to VHS HQ produced 250 lines, so that overall a Betamax/VHS user could expect virtually identical luminance and chrominance resolution (~30 lines across), wherein the actual picture performance depended on other factors, including the condition and quality of the videotape, and the specific video recorder machine model.

Betamax held an early lead in the format war — but by 1981, U.S. Betamax sales had sunk to only 25% of all sales.

Slow decline

The VHS VCR was a mainstay in the TV-equipped living room for more than a decade, but is being replaced by newer technologies. For time-shifting (off the air or cable/satellite taping), hard-drive based DVRs have replaced the VCR as the time-shifting device of choice, especially in households with subscriber-based TV-services. The home camcorder market, one which VHS shared with alternative formats, has already transitioned to digital-video recording. But the largest blow to VHS was the March 1997 introduction of the DVD format to American consumers. For home-video (that is, pre-recorded commercially-released movies, etc.) rental and sales, DVD has completely taken the place of VHS.

At most electronics retailers, choice among VHS equipment is increasingly shrinking. New sales are focused on DVD-recorders and subscriber-based DVRs (such as TiVo). Most electronics chains have stopped stocking VHS home-video releases, focusing only on DVD and Blu-ray Disc technology. Major Hollywood studios no longer issue releases on VHS. The final major Hollywood motion picture released on VHS was David Cronenberg's A History of Violence. However, home-video VHS tapes can still be found in many second-hand shops, and are sometimes very cheap due to the lack of demand.

On December 31, 2008, the final truckload in the USA of recorded programming on VHS tapes rolled out of a warehouse owned by Ryan Kugler, the last major supplier of VHS-recorded videos. Kugler is President and co-owner of Distribution Video Audio, a seller of distressed goods such as VHS tapes. According to Kugler, "It's dead, this is it, this is the last Christmas, without a doubt. I was the last one buying VHS and the last one selling it, and I'm done. Anything left in warehouse we'll just give away or throw away."

Although VHS has quickly faded from mainstream home-video, the VCR is still used in many US households. The Washington Post noted that as of 2005, 94.5 million Americans still owned VHS format VCRs.

The last standalone JVC VHS-only unit was produced on December 31, 2008. JVC, like many other manufacturers, still makes combination DVD+VHS units.

Several retail chains in the United States and in Europe planned to stop selling VHS equipment in 2004, 2005, and 2006. Despite these plans, VHS recorders and blank tapes are still being sold in major stores worldwide. As an acknowledgment of VHS popularity, in 2009 Panasonic has announced the world’s first dual deck VHS-Blu-ray player.

Successors

DVD

The DVD-Video format was introduced first, in 1996, in Japan, to the United States in March 1997 (Test Marketed) and mid-late 1998 in Europe and Australia.

Despite DVD's better quality (480 typical versus 250 lines horizontal resolution), 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 unreliable, as well as the risk of scratches and hairline cracks.
• Incompatibilities in playing discs recorded on a different manufacturer's machines to that of the original recording machine.
• Shorter recording time: Up to six hours on a single-layer disc (with high compression) versus approximately 12 hours on a T-240 or DF420 tape.
• Compression artifacts: MPEG-2 video compression can result in visible artifacts such as macroblocking, mosquito noise and ringing which become accentuated in extended recording modes (more than three hours on a DVD-5 disc). Standard VHS will also result in reduced luminance resolution which will make the picture look horizontally blurred (resolution decreases further with LP and EP recording modes).

Blu-ray Disc

A newer optical disc format is Blu-ray Disc, which is the designed successor to DVD. A single Blu-ray Disc can hold up to 50GB (over 5X the memory of DVD) of information including up to 1080p High-definition video, high definition photos, music, and more.

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 set-top boxes
• Hard disk/optical disc combination set-top boxes
• Personal computer-based media center

Hard disk-based systems include TiVo as well as other digital video recorder offerings. These types of systems provide users with a no-maintenance solution for capturing video content. Customers of subscriber-based TV generally receive electronic program guides, enabling one-touch setup of a recording schedule. Hard disk-based systems allow for many hours of recording without user-maintenance. For example, a 120 GB system recording at an extended recording rate (XP) of 10 Mbit/s MPEG-2 can record over 25 hours of video content.

References

External links

• BBC News article: Death of video recorder in sight
• HowStuffWorks: How VCRs work
• The 'Total Rewind' VCR museum covering the history of VHS and other vintage formats