From Retro CDN
S-Video (also known as Y/C) is a baseband analog video format offering a higher quality signal than composite video, but a lower quality than RGB and component video. This mid-level format divides the signal into two channels - luminance and chrominance.
The luminance signal and modulated chrominance subcarrier 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, however, separates the two, so low-pass filtering is not necessary. This increases bandwidth for the luminance information, and also subdues the color crosstalk problem.
While the luminance performance of S-Video compares favorably to analog component video, the chrominance performance--aside from reduced crosstalk--does not show notable improvement over composite video.
S-Video signals tend to degrade considerably when transmitted across more than 5 meters of cable. For long distances, component or composite video may provide better quality.
Today, S-Video signals are generally connected using 4-pin mini-DIN connectors using a 75 ohm termination impedance. The pins in the connectors bend easily, hence care must be taken when plugging the cables in--else a pin is likely to bend, causing the loss of color, corruption of the signal, or complete loss of the signal.
Before the mini-DIN plug became standard, S-Video signals were often carried through different types of plugs. For example, the Commodore 64 home computer of the 1980s, one of the first widely available devices to feature S-Video output, used an 8-pin standard size DIN plug on the computer end and a pair of RCA plugs on the monitor end. Also, Sony's 3/4" U-matic format machines can transfer Y/C over a proprietary 7-pin connector commonly referred to as a "DUB" connector.
Today, S-Video signals can be transferred through SCART connections as well. However the SCART connector must explicitly support S-Video as it is not part of the original SCART standard.
S-Video is commonly used on consumer DVD players, VCRs, and modern game consoles. It is also widely available on modern professional equipment and computer video capture and playback cards.