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What is SDI?

What is SDI?

SDI-Serial Digital Interface, widely used in SDI encoders, SDI converters and other equipment, which has been applied to radio and television fields, security monitoring. And we have witnessed the development of the video standard with the ultra high definition standard from SD-SDI, HD-SDI to 3G-SDI, 6G-SDI, 12G-SDI and 24G-SDI. At the same time, it has also promoted an era of a new digitized video display in both monitoring and radio and television fields. Below we discuss the difference between the various SDI interface.


12G-SDI information and products tour by DELTACAST - Deltacast


SDI: Serial Digital Interface (SDI) is a family of digital video interfaces first standardized by SMPTE (Society of Motion Picture and Television Engineers) in 1989. For example, ITU-R BT.656 and SMPTE 259M are defined for broadcast-grade video.

SD-SDI: The SD-SDI standard support the 270 Mb/s bit rate. SD-SDI is used to transmitting low-resolution PAL compatible video 720 * 576 @ 25fps and uses a clock rate of 27 MHz. In 1994, ITU-R (formerly International Radio Consultative Committee) released Recommendation BT.656-2, incorporating the new serial digital interface defined in EBU Tech.3267 and SMPTE 259M, which uses 10-bit transmission and non- Zero Reverse (NRZI) encoding. The clock rate was 270 Mb / s when transmitting a 4: 2: 2 level signal from ITU-R BT. 601 (part A), at which point the SD-SDI standard was defined, which is today’s SDI.

HD-SDI: The standard known as the HD Serial Digital Interface (HD-SDI) is standardized in SMPTE 292M; Although this standard is known as the 1.5 Gb / s interface, the bit rates supported by HD-SDI are actually 1.485 Gb / s and 1.485 / 1.001 Gb/s. OPTCORE provides a wide line of HD-SDI SFP transceiver for the special broadcast application.

3G-SDI: This standard is known as the 3 Gb/s interface, but the actual bit rates are 2.97 Gb / s and 2.97 / 1.001 Gb / s. 3G-SDI supports several different mapping levels, as described in the SMPTE ST425-1 standard. These levels are called A, B-DL, and B-DS. Like the HD-SDI standard, the 3G-SDI supports 3G-SDI CRC generation and checking as well as line number insertion and capture.

6G-SDI: This standard defines a bit-serial data structure, electrical signal and coaxial cable interface for the transport of signals with a total payload of 5.940 Gb/s or 5.940/1.001 Gb/s. This standard also specifies the electrical and physical characteristics of coaxial cables and connectors. This standard defines several mapping modes for the carriage 2160-line and 1080-line image formats and associated ancillary data into a Single-link 6 Gb/s [nominal] SDI bit-serial interface.

12G-SDI: The 12G-SDI is an SDI standard developed to support higher resolution, frame rate, and color fidelity. It provides four times the bandwidth of HD, carrying 12Gbps, making it ideal for the 4K 60p format. This is not new, UG has been developed 6G / 12G since 2012, but has not been approved by the standard governing body SMPTE (Society of Motion Picture and Television Engineers) under the SMPTE ST-2082 draft name. Click to learn more about 12G-SDI transceiver.


Serial digital interface (SDI) is a family of digital video interfaces first standardized by SMPTE (The Society of Motion Picture and Television Engineers) in 1989. For example, ITU-R BT.656 and SMPTE 259M define digital video interfaces 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.

Additional SDI standards have been introduced to support increasing video resolutions (HD, UHD and beyond), frame rates, stereoscopic (3D) video,[4][5] and color depth. Dual link HD-SDI consists of a pair of SMPTE 292M links, standardized by SMPTE 372M in 1998; this provides a nominal 2.970 Gbit/s interface used in applications (such as digital cinema or HDTV 1080P) that require greater fidelity and resolution than standard HDTV can provide. 3G-SDI (standardized in SMPTE 424M) consists of a single 2.970 Gbit/s serial link that allows replacing dual link HD-SDI. 6G-SDI and 12G-SDI standards were published on March 19, 2015.

These standards are used for transmission of uncompressed, unencrypted digital video signals (optionally including embedded audio and time code) within television facilities; they can also be used for packetized data. SDI is used to connect together different pieces of equipment such as recorders, monitors, PCs and vision mixers. Coaxial variants of the specification range in length but are typically less than 300 meters (980 ft). Fiber optic variants of the specification such as 297M allow for long-distance transmission limited only by maximum fiber length or repeaters. SDI and HD-SDI are usually available only in professional video equipment because various licensing agreements restrict the use of unencrypted digital interfaces, such as SDI, prohibiting their use in consumer equipment. Several professional video and HD-video capable DSLR cameras and all uncompressed video capable consumer cameras use the HDMI interface, often called clean HDMI. 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.


Last but not least as regards benefits, the SDI standard carries both the video signal and time code in one cable. Other interfaces, such as HDMI or DVI, have no time code support, while DisplayPort does.


With the 24G-SDI standard in development – which will support 8K, 120p resolution – there is no doubt that the SDI standard will be around for a long time. Having seen the first 8K projector (by Digital Projection) and how they ran 16 3G/HD-SDI cables into it for a single 8K feed – it’s obvious that we need to step up the race for higher resolutions. And SMPTE seems to have done just that by being close to publishing the 24G-SDI standard!