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Definition: SDI


(1) See software-defined infrastructure, Single Document Interface, Strategic Defense Initiative and Switched Digital International.

(2) (Serial Digital Interface) SDI is a unidirectional video interface. Standardized by SMPTE in the late 1980s, SDI has been the primary interface for transmitting uncompressed digital video signals. SDI will eventually be replaced by IP-based NDI, and the many cables used in broadcasting facilities will be replaced with an Ethernet topography. See NDI.

SDI uses a high grade of coaxial cable and a BNC connector with Teflon insulation. It also supports optical fibers with ST, SC and FC connectors. Following are the common formats transmitted over SDI. See ITU-R BT.601, BNC connector, fiber-optic connectors and serial interface.

 SD-SDI                  Aspect  Transfer
 (Standard Definition)   Ratio   Rate
 Digitized NTSC (4FSC)    4:3    143 Mbps
 Digitized PAL (4FSC)     4:3    177 Mbps
 Component ITU-R BT.601   4:3    270 Mbps
 Component ITU-R BT.601  16:9    360 Mbps

 HD-SDI (High Definition)  See HD-SDI.
 Component ITU-R BT.709  16:9  1,485 Mbps
 Dual-link (two cables)        2,970 Mbps

 3G-SDI (3 Gbps)
 One-cable version of HD-SDI   2,970 Mbps





Blackmagic SDI Capture Board
Two sockets are input, and two are output. At 4:2:2 color sampling, SDI uses one line for in or out. However, HD-SDI at 4:4:4 requires two lines. See chroma subsampling. (Image courtesy of Blackmagic Design Pty. Ltd, www.blackmagicdesign.com)