CVBS - video signal transmission standard

Composite Video also referred to as the CVBS (Composite Video Baseband Signal) is an analogue video transmission signal without audio which contains image data in standard resolution of 480 and 570 or (480 lines or 576 lines interlaced).

The video data is encoded in a single channel and unlike slightly higher resolution S-Video using two channels and higher quality Component Video using three or more channels.

Composite Video is often transmitted using standard formats including PAL, NTSC and SECAM and is often referred to as CVBS.

Fig. 1. Single CVBS signal line (without chrominance signal)

A composite video signal combines information required to broadcast a colour video as well as frame and line synchronisation pulses in a single cable. Video signal colour is a linear combination of image brightness and modular sub-carrier chrominance transmitting information about the colour and a combination of hue and saturation. The coding process details differ between PAL, SECAM and NTSC systems.

A combination of chrominance and luminance is actually a frequency division technique, however, it is much more complex than a typical frequency division multiplexing system i.e. used in analogue radio station multiplexing in AM and FM bands.

CVBS signal includes a "ColourBurst" signal (colour sync signal) at the beginning of each scan line, based on which the receiver can restore the attenuated carrier chrominance signals (colour) and thus decode the colour information. Colour sync signal is phase reversed (180° from the phase) in relation to the reference sub-carrier.

Composite Video signal can be easily directed to each transmission channel by modulating a corresponding RF carrier wave with the signal. During CVBS signal broadcast on different devices, the signal can be output at VHF and UHF frequency, i.e. it can be broadcasted on a selected TV channel.

In home applications, the composite video signal is usually connected via RCA (cinch) port usually marked yellow. High quality coaxial cables often use BNC connectors, e.g. TV studios, digital CCTV recorders and post-production.