Serial Digital Interface (SDI) refers to a family of video interfaces standardized by SMPTE. It is a standard in the broadcast Industry for digital video transmission over coaxial cable. For example, ITU-R BT.656 and SMPTE 259M define digital video interfaces used for broadcast-grade video. A related standard, known as high-definition serial digital interface (HD-SDI), is standardized in SMPTE 292M; this provides a nominal data rate of 1.485 Gbit/s.

The most common data speed is 270 megabits per second (Mbps). However, speeds of up to 540 Mbps are theoretically possible. Standard 75-ohm cable is used. This is the same type of coaxial cable used in most home television (TV) installations.

The SDI standard uses data words that are 8 or 10 bits in length. Signals are uncompressed and are self-synchronizing between the source (transmitter) and destination (receiver). Most errors caused by noise or interference can be detected, and the lost data recovered by means of a specialized code called the Hamming code. A signal in SDI can contain up to four independent digital audio signals along with the video signal.