SDI (Serial Digital Interface) is a format for transmitting video over cable, being standardized by SMPTE (Society of Motion Picture and Television Engineers). These standards are especially used for transmission of uncompressed, unencrypted digital video signals (optionally including embedded Audio and/or Time Code) within television facilities. 

Standard Name Bitrates Example Video
SMPTE 259M  SD-SDI 270 Mbit/s, 360 Mbit/s, 143 Mbit/s, and 177 Mbit/s 480i, 576i
SMPTE 344M  ED-SDI 540 Mbit/s 480p, 576p
SMPTE 292M  HD-SDI 1.485 Gbit/s, and 1.485/1.001 Gbit/s 720p, 1080i
SMPTE 372M  Dual Link HD-SDI 2.970 Gbit/s, and 2.970/1.001 Gbit/s 1080p
SMPTE 424M  3G-SDI 2.970 Gbit/s, and 2.970/1.001 Gbit/s 1080p