The Serial Digital Interface (SDI), standardized in ITU-R BT.656 and SMPTE 259M, is a digital video interface 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. An emerging interface, commonly known in the industry as dual link and consisting essentially of a pair of SMPTE 292M links, is standardized in SMPTE 372M; this provides a nominal 2.970 Gbit/s interface used in applications (such as digital cinema) that require greater fidelity and resolution than standard HDTV can provide. A more recent interface, consisting of a single 2.97 Gbit/s serial link, is standardized in SMPTE 424M.
These standards are used for transmission of uncompressed, unencrypted digital video signals (optionally including embedded audio) within television facilities; they can also be used for packetized data. They are designed for operation over short distances; due to their high bitrates they are inappropriate for long-distance transmission. SDI and HD-SDI are currently only available in professional video equipment; various licensing agreements, restricting the use of unencrypted digital interfaces to professional equipment, prohibit their use in consumer equipment. (There are various mod kits for existing DVD players and other devices, which allow a user to add a serial digital interface to these devices).
