Serial Digital Interface carries uncompressed video, multiple tracks of embedded audio and ancillary data usually over the ubiquitous 75-ohm coax cable, terminated in a BNC connector. As the demands of television have grown so SDI has risen to the challenge to continue providing a reliable plug-and-play connection. Today there are many types to fit with the demands for bigger and faster video formats.
SDI SMPTE 259M – for SD 4:2:2 digital television, is based on a 270 Mb/s transfer rate. This is a 10-bit, scrambled, polarity-independent interface, with common scrambling for both component ITU-R BT.601 and composite digital video and four groups each of four channels of embedded digital audio. Most broadcast video equipment includes SDI which greatly simplifies its installation and signal distribution. It can transmit the signal up to 350 meters (depending on cable quality and connected equipment, specifically distribution amplifiers and routers).
HD-SDI is standardized in SMPTE 292M is for 4:2:2 HD television. The serial bit-stream runs at 1.485 Gb/s to carry up to 10-bit Y,Cr,Cb component video as well as embedded audio and ancillary data. The interface is also specified for fiber for distances up to 2 km.
3G-SDI (SMPTE 424M) operates at 2.97 Gb/s, twice the clock rate HD-SDI and is designed to carry high bandwidth HD television such as 1080/50P, 1080/60P, HD RGB, as well as 2K DI images.
6G-SDI (not yet standardized) operates at 5.94 Gb/s and can carry 4K at up to 30P.
12G-SDI (not yet standardized) operates at 11.88 Gb/s can carry 4K at up to 60P frame rate.
The higher bit rates can work over shorter lengths of coax and Fibre Optic versions can be used for the larger/faster frame-rate formats over longer distances.