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VHS

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VHS Logo
VHS Logo
Top view VHS cassette with U.S. Quarter for scale
File:Vhs cassette bottom.jpg
Bottom view of VHS cassette with magnetic tape exposed

The Video Home System, first released in September 1976, better known by its abbreviation VHS, is a recording and playing standard for video cassette recorders (VCRs), developed by JVC (with some of its critical technology under lucrative licensing agreements with Sony) and launched in 1976. VHS officially stands for Video Home System, but it initially stood for Vertical Helical Scan, after the relative head/tape scan technique. Some early reports claim the name originally stood for Victor Helical Scan System.

VHS became a standard format for consumer recording and viewing in the 1980s and 1990s after competing in a fierce format war with Sony'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. 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 due to improved engineering, head-tape contact is no longer an impediment to fast winding.

Technical details

A VHS cassette contains 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) halves the tape speed and doubles the recording time, while EP mode (for NTSC, 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. An unofficial LP mode with half the standard speed exists on some NTSC machines, but is not part of the VHS standard.

VHS tapes have approximately 3 MHz of video bandwidth, and a horizontal resolution of about 240 discernible lines per scanline [1]. The frequency modulation of the luminance signal makes higher resolutions impossible within the VHS standard, no matter how advanced the recorder's technology. The vertical resolution of VHS (and all other analog recording methods) is determined by the TV standard — a maximum of 486 lines are visible in NTSC and a maximum of 576 lines in PAL.

The video bandwidth is achieved with 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 (monaural) linear track at the upper edge of the tape, which was limited in frequency response by the tape speed. More recent hi-fi VCRs add higher-quality stereo audio tracks 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 hi-fi VHS has gained it some popularity as an audio format in certain applications; in particular, ordinary home hi-fi 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.

Of course, for backward compatibility, hi-fi VCRs still write the linear audio track during recording, and can automatically read it during playback if the hi-fi audio is not present.

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've 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. These advanced features are impossible to find on later-model VCRs due to the rise of digital video formats.

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 track 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.

Variations

Several improved versions of VHS exist, most notably S-VHS, an improved analog standard, and D-VHS, which records digital 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. W-VHS caters for high definition video.

Another variant is VHS-C (C for compact), used in some 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 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.

There is also a JVC-designed component digital professional production format known as Digital-S or (officially) 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 analogue television signals in existance 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, many parts of Asia and Africa)
  • SECAM/625/25 (SECAM, French variety)
  • MESECAM/625/25 (most other SECAM countries, notably Eastern Europe 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 multistandard VHS machines have become more and more common. These can handle VHS tapes of more than one standards. E.g. regular VHS machines sold in 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. Likewhise, S-VHS machines for the Brazilian market record in NTSC and convert to/from PAL-M.

Tape Lengths

All VHS cassette shells are compatible (as opposed to the signal recorded on the tape, which is not). However, as tape speeds differ between NTSC and PAL/SECAM, so do playing times. 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 use 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 than indicated. It can easily be derived by multiplying with 3/2 or 2/3, respecively.

E.g. a T-120 tape plays 120 minutes in NTSC-SP, but 180 minutes in PAL-SP. Conversely, an E-300 tape plays 300 minutes in PAL-SP, but 200 minutes in NTSC-SP.

VHS vs. Betamax

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's technical specifications are better on paper, it is often stated that VHS' eventual victory was a victory of marketing over technical excellence. In fact, however, the root causes of VHS' victory are somewhat more complex. Betamax held an early lead in the format war, but by 1980 VHS was gaining due to its longer tape time (2 hours at SP) and JVC's less strict licensing program. Ultimately Betamax did manage to make up the difference on recording time, but this was too little, too late. Sony ultimately conceded the fight in the late '80s, bringing out a line of VHS VCRs. Betamax survived as a professional format, but VHS had no serious competitors in the home video market until the arrival of DVD and digital video recorders.

Other formats such as 8mm video cassettes and MiniDV have emerged since, but these formats are by no means in complete competition with VHS. As these cassettes are much more compact in design — which also means the hardware to play and record the tapes has to be more compact than VHS, and therefore more expensive — they are much more suited to portable applications such as camcorders. 8mm 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 8mm 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, it offers superior audiovisual quality, and the storage of data in digital format on tape makes for improved transfer and editing.

DVD and the decline of VHS

The DVD (digital versatile disc) format was introduced in 1996 and has since overtaken VHS in sales and rentals. Major U.S. retailers Circuit City and Best Buy stopped selling VHS tapes in 2002 and 2003, respectively. Many films released to theaters from 2004 onwards have later been released only on DVD and not on VHS, and many other new feature films are being released solely on DVD. Moreover, most television programs released as box sets are for sale in DVD format only. Commentators predict that 2006 will be the final year of new releases on VHS, as major studios continue to phase out VHS.

Despite DVD's better quality, however, VHS is still widely used in home recording of television programs, due to the large installed base and the lower cost of VHS recorders. It can also be more convenient to use VHS tapes because they can be rewritten easily, and VCRs can be easier than DVD recorders to use.

File:VHSC.jpg
Bottom and top view of VHS-C compact video cassette
File:VHSC Carrier.jpg
Example of a VHS-C adapter


List of notable VHS companies

See also

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