composite video, blanking, and sync

Composite video is a single analog signal that carries picture information, timing pulses, and control data all on one wire. The signal combines luminance (brightness), chrominance (color), blanking intervals, and synchronization pulses into a standardized waveform. This bundled approach made composite video the dominant standard for consumer and industrial video distribution for several decades, from the 1950s through the early 2000s, because it required only one coaxial cable instead of multiple parallel paths.

The signal structure obeys strict timing rules. Blanking intervals are periods when the electron beam in a cathode-ray tube returns to the start of a new line or field, and the video level is forced to black to prevent visible scan lines from appearing on screen. Sync pulses are voltage drops within the blanking interval that tell the display hardware exactly when to start drawing each line and each field. In NTSC (North American and Japanese standard), horizontal sync occurs every 63.5 microseconds; in PAL and SECAM (European and Soviet standards), every 64 microseconds. Vertical sync occurs once per field (roughly 60 Hz in NTSC, 50 Hz in PAL). The blanking and sync information occupies roughly 25 percent of the composite video signal's bandwidth.

Technical variants and impedance

Composite video signals typically run at 0.714 volts peak-to-peak (NTSC) or 0.7 volts (PAL), measured from blanking level to peak white. The signal is impedance-matched to 75 ohms, and terminated with a 75-ohm resistor at the display end. Yellow RCA connectors became the de facto connector standard, though BNC connectors and threaded F-connectors appear in professional broadcast and cable television equipment. Impedance mismatches cause signal reflections visible as ghosting or smearing in the picture.

The chief weakness of composite video is color distortion. Luminance and chrominance data share the same wire, and they can interfere with each other, particularly in color transitions or when transmitted over long cable runs. Industrial systems using composite video for closed-circuit television, surveillance, or machine vision often encounter cross-color artifacts, where color information bleeds into adjacent lines. Composite video also cannot carry sound; audio must travel on a separate cable or on a different frequency band.

Composite video gradually gave way to S-video (which separates luminance and chrominance), component video (three separate signals), and eventually digital formats like SDI and HDMI. However, composite video remains common in legacy broadcast equipment, industrial cameras, medical imaging displays, and arcade games. Any new system specifying composite video today is usually constrained by cost, backward compatibility, or lack of upgrade budget rather than technical preference.