S-Video: Difference between revisions
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==Connector== |
==Connector== |
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S-Video signals are generally connected using 4 pin [[mini-DIN]] connectors using a 75 [[ohm (unit)|ohm]] termination impedance. Apart from the impedance requirement, these cables are equivalent to regular mini-DIN cables (like Apple's [[Apple Desktop Bus|ADB]]); these cables can be used for S-Video transfer if no other cable is available, but picture quality may not be as good. Due to the wide use of S-Video connections for DVD players |
S-Video signals are generally connected using 4 pin [[mini-DIN]] connectors using a 75 [[ohm (unit)|ohm]] termination impedance. Apart from the impedance requirement, these cables are equivalent to regular mini-DIN cables (like Apple's [[Apple Desktop Bus|ADB]]); these cables can be used for S-Video transfer if no other cable is available, but picture quality may not be as good. Due to the wide use of S-Video connections for DVD players, S-Video cables are fairly inexpensive compared to component or digital connector cables, and are routinely available in places where the higher-bandwidth cables are not. |
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The mini-DIN pins, being weak, sometimes bend. This can result in the loss of color, or other corruption (or loss) in the signal. A bent pin can be forced back into shape, but this carries the risk of further damage, or even the pin breaking off. |
The mini-DIN pins, being weak, sometimes bend. This can result in the loss of color, or other corruption (or loss) in the signal. A bent pin can be forced back into shape, but this carries the risk of further damage, or even the pin breaking off. |
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Revision as of 20:10, 6 August 2007
 A standard 4-pin S-Video cable connector, with each signal pin paired with its own ground pin. | |||
| Type | Analogue video connector | ||
|---|---|---|---|
| General specifications | |||
| Hot pluggable | yes | ||
| External | yes | ||
| Video signal | NTSC, PAL or SECAM video | ||
| Pins | 4 or 7 | ||
| Connector | Mini-DIN connector | ||
| Pinout | |||
 | |||
| Connector Pinout (looking at the socket). | |||
| Pin 1 | GND | Ground (Y) | |
| Pin 2 | GND | Ground (C) | |
| Pin 3 | Y | Intensity (Luminance) | |
| Pin 4 | C | Color (Chrominance) | |
Separate video, abbreviated S-Video and also known as Y/C (or erroneously, S-VHS and "super video") is an analog video signal that carries the video data as two separate signals (brightness and color), unlike composite video which carries the entire set of signals in one signal line. S-Video, as most commonly implemented, carries high-bandwidth 480i or 576i resolution video, i.e. standard definition video. It does not carry audio on the same cable.
The 4-pin Mini-DIN connector (shown at right) is the most common of several types of S-Video connectors. Other S-Video connector variants include 7-pin locking "dub" connectors used on many professional S-VHS machines, and dual "Y" and "C" BNC connectors, often used for S-Video patch bays. Early Y/C video monitors often used RCA connectors that were switchable between Y/C and composite video input. Though the connectors are different, the Y/C signals for all types are compatible.
Overview
The luminance (Y; greyscale) signal and modulated chrominance (C; colour) information are carried on separate synchronized signal/ground pairs.
In composite video, the luminance signal is low-pass filtered to prevent crosstalk between high-frequency luminance information and the color subcarrier. S-Video separates the two, and detrimental low-pass filtering is unnecessary. This increases bandwidth for the luminance information, and also subdues the color crosstalk problem. The infamous dot crawl is eliminated. This means that S-Video leaves more information from the original video intact, thus having a much-improved image reproduction compared to composite video.
Due to the separation of the video into brightness and colour components, S-Video is sometimes considered a type of component video signal, although it is also the most inferior of them, quality-wise, being far surpassed by the more complex component video schemes (like RGB). What differentiates S-Video from these higher component video schemes is that S-Video carries the colour information as one signal. This means that the colours have to be encoded in some way, and as such NTSC, PAL and SECAM signals are all decidedly different through S-Video. Thus, for full compatibility the used devices not only have to be S-Video compatible but also compatible in terms of colour encoding. In addition, S-video suffers from reduced color resolution. For NTSC S-video's color resolution is typically 120 lines (versus 270 lines for a DVD-encoded signal, or 60 lines for VHS/betamax).
When used for connecting a video source to a video display where both support 4:3 and 16:9 display formats, the PAL television standard provides for signalling pulses that will automatically switch the display from one format to the other. The S-video connection transparently supports this operation. The S-Video connection also has general provision for widescreen signalling through a DC offset applied to the chrominance signal; however, this is a more recent development, and is not widely supported.
Connector
S-Video signals are generally connected using 4 pin mini-DIN connectors using a 75 ohm termination impedance. Apart from the impedance requirement, these cables are equivalent to regular mini-DIN cables (like Apple's ADB); these cables can be used for S-Video transfer if no other cable is available, but picture quality may not be as good. Due to the wide use of S-Video connections for DVD players, S-Video cables are fairly inexpensive compared to component or digital connector cables, and are routinely available in places where the higher-bandwidth cables are not.
The mini-DIN pins, being weak, sometimes bend. This can result in the loss of color, or other corruption (or loss) in the signal. A bent pin can be forced back into shape, but this carries the risk of further damage, or even the pin breaking off.
it for this reason. Also, S-Video and RGB are mutually exclusive through SCART, due to the S-Video implementation using the pins allocated for RGB. Most SCART-equipped televisions or VCRs (and almost all of the older ones) do not actually support S-Video, resulting in a black-and-white picture if such a connection is attempted, as only the luminance signal portion is usable. Generally, a black-and-white picture in itself can also be a sign of incompatible colour encoding—for example NTSC material viewed through a PAL-only device.
A 'hack' exists to possibly attain color on devices that do not support S-Video through SCART. This is done via joining the pins 15 and 20 in the SCART connector (either directly or using a 470pF capacitor), but may not yield optimal results; camp0s.com S-Video hack
A similar hack also allows color. This connects the Y and C (3 and 4) pins on the S-Video connector; chinastillcool.co.uk S-Video hack
Specifications
The 4-pin mini-DIN connectors seem to be common on TVs, VCRs, and DVD players. The 7-pin quasi-DIN connectors seem to be more common on computers. The 7-pin socket accepts the 4-pin plug and the S-video signals are available on the matching pins. When a 7-pin plug is inserted, one of the extra pins carries a composite CVBS video signal for non S-video displays. Some graphics cards require the remaining two pins to be shorted together to enable the CVBS mode.
The 7-pin plug has a longer locating lug making it difficult (but not impossible) to insert it in a 4 pin socket. Damage to the plug and socket is inevitable if the plug is forced into the socket.
A 7-pin quasi-DIN can also transmit Y'PbPr or RGB component video, though the outputs are usually 3 RCA jacks. Such cables are often provided with video cards.
Usage
S-Video is commonly used in U.S., Canada, Australia, and Japan, found there on consumer TVs, DVD players, high-end video cassette recorders, Digital TV receivers, DVRs, and game consoles. Almost all TV-out connectors on graphics cards are S-Video, even in Europe, where the standard failed to make a significant impact (beyond camcorders) due to the preference for the higher-quality RGB signal provided by SCART.
S-Video cables are used for computer to TV output for business or home usage. Because it is very simple to convert S-Video to composite signal (just the logical merging of the two through a filter capacitor is required), many electronics retailers offer converter adaptors for signal conversion. No conversion will improve image quality, but will allow connecting to otherwise-incompatible devices. Converting composite signal to S-Video is a little harder, because once Luminance and Color are merged together it is hard to take them apart without loss.
Due to a lack of bandwidth, S-Video connections are generally not considered suitable for high-definition video signals. As a result, HD sources are generally connected to a monitor by way of analog component video or wideband digital methods (usually HDMI or DVI).
The situation with VCRs is a bit unusual; the common S-Video connector was designed for Super VHS VCRs as a high-bandwidth video connection, and has been used for the same purpose on a great number of other consumer devices, coming into greatest prominence with the rise of the DVD format. Many digital, and all Hi-8, and S-VHS-C camcorders support S-Video out as well. Standard VHS VCRs do not put out a high enough resolution signal to saturate an S-Video connection, and therefore most such units, even those in combination units with DVD players (which commonly use S-Video or component outputs), require the output from the VHS deck to go through a composite video or RF connection.
See also
References
This article is based on material taken from the Free On-line Dictionary of Computing prior to 1 November 2008 and incorporated under the "relicensing" terms of the GFDL, version 1.3 or later.