What is Composite Video?

 

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Composite video is a format for analog television signals before they are combined with sound signals and modulated onto an RF carrier; the signal is picture-only before the combination. The signal is often formatted in either NTSC, PAL, or SECAM and is a composite of three signals, Y, U, and V, each with an individual sync pulse. Y carries picture luminance and synchronizing information; it can thus be displayed, by itself, on a monochrome display. U and V are combined to carry color information via a signal called chrominance, formed after UV passes through two orthogonal phases of a color carrier signal. To form the composite, Y and UV are combined. Since Y is a baseband signal and UV are combined with a carrier, in this case a color carrier, composite video is essentially frequency-division multiplexing.

 

In North America, consumer composite video is carried largely by RCA-style cables and, to a lesser extent, S-video cabling. RCA cabling, a type of electrical cable so named for its designer, the Radio Corporation of America, was originally developed to standardize phonograph-amplifier connectivity. RCA cabling is a mixture of three individual cables, two for audio and one for video. Composite video is carried on the yellow connector, while audio is carried on the red and white/black connectors.
In Europe, composite video is carried over SCART, a standardized A/V cabling system developed by the French in the late 1970s.

In many analog home video applications, especially VCRs and some early computers, the outputted video signal was composite. Users then had a choice between displaying the raw signal via an RCA-style cable or modulating it with either VHF or UHF and displaying it on an individual TV channel (usually channel 3 in the United States).
   
 

 

Usages/Applications

  • Composite video is used to carry analog video signals from an output source--be it from a VCR, DVD player, computer, cable box, or camcorder—and connect to TVs, computer monitors, and other displays.
  • RCA-style cables can be adapted for a number of uses besides carrying composite video, including power, RF, and loudspeakers.

 

Practical Data

  • Typically, RCA-style composite video cables are limited to 100 feet in length for practical reasons. S-video cables are usually produced at similar maximum lengths.
  • The S-video standard is actually an improved extension of composite video. S-video utilizes a 4-pin DIN-style connector to carry two main signals, luma (brightness, similar to composite's luminance) and chroma (color, similar to chrominance). By separating the two signals, S-video eliminates the need for composite video's low-pass filtering, leaving more video signal intact and eliminating the infamous dot crawl.

 
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