SMPTE digital video transmission standard for professional cameras and monitors. Carries HD to 4K signals with embedded audio and metadata over coaxial cable up to 100 meters.
Technical Details
SD-SDI transmits 525/625-line signals at 270 Mbps, HD-SDI carries 1080i/720p material at 1.485 Gbps over distances up to 100 meters with RG-6 cables. 3G-SDI doubles the bandwidth to 2.97 Gbps for 1080p60 signals, while 6G-SDI (6 Gbps) and 12G-SDI (11.88 Gbps) support 4K UHD formats. Signal transmission occurs via NRZ (Non-Return-to-Zero) with embedded sync, audio, and metadata. For longer distances, fiber optic cables are used, enabling transmissions over several kilometers.
History & Development
SMPTE developed SDI in 1989 as the digital successor to analog composite and component video signals. The first SD-SDI standard, SMPTE 259M, became established in broadcast studios from 1995 onwards. HD-SDI followed in 1998 with SMPTE 292M, and 3G-SDI in 2006 with SMPTE 424M. The 6G and 12G variants emerged in 2015 in response to 4K requirements. Manufacturers such as Sony, Panasonic, and Blackmagic Design successively integrated SDI into cameras, recorders, and monitoring equipment.
Practical Use in Film
Film productions utilize SDI for uninterrupted signal paths between cameras, video assist, DIT stations, and client monitors. On "Mad Max: Fury Road" (2015), 3G-SDI enabled the simultaneous transmission of over 20 camera signals to the video village. Documentary filmmakers value SDI for its latency-free transmission for live monitoring of critical scenes. The standard supports embedded timecode and metadata transmission, essential for multi-cam workflows and post-production synchronization.
Comparison & Alternatives
Unlike HDMI, SDI offers longer transmission distances, robust locking mechanisms, and professional signal stability. While NDI (Network Device Interface) enables IP-based video transmission over Ethernet, SDI remains the standard for time-critical live productions. Modern alternatives such as USB-C with DisplayPort Alt Mode or wireless systems from Teradek complement SDI but do not replace it in mission-critical applications. In pure IP workflows, SMPTE ST 2110 is gaining importance.