SDI, HD-SDI, 3G-SDI, 6G-SDI, 12G & 24G-SDI - Optcore

Initial Published: November 21,

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Serial Digital Interface(SDI) is a digital video standard for the broadcast industry. This standard is widely used in SDI encoders, SDI converters, and other equipment, including radio and television scenarios and security monitoring. We have witnessed the development of the video standard with ultra-high definition standards, from SD-SDI and HD-SDI to 3G-SDI, 6G-SDI, 12G-SDI, 24G-SDI, and 48G-SDI. This article will focus on this topic and provide a definitive guide. 

Table of Contents

What is the serial digital interface (SDI)?

Serial Digital Interface (SDI) is a family of digital video interfaces first standardized by SMPTE (Society of Motion Picture and Television Engineers) in . It is a standard for transmitting uncompressed digital video and audio using coaxial or fiber-optic cables.

The SDI interface can not directly transmit the compressed digital signal. Therefore, the system must decompress the compressed signal recorded by digital video recorders, hard disks, and other equipment and then enter the SDI system to travel.

However, repeated decompression and compression will cause image quality degradation and increased latency. Therefore, various formats of digital video recorders and non-linear editing systems have provisions of their own for the direct transmission of the compressed digital signal interface.

The table below shows the history of the evolution of the standards.

StandardNameIntroducedBitratesExample video formatsSMPTE 259MSD-SDI Mbit/s, 360 Mbit/s, 143 Mbit/s, and 177 Mbit/s480i, 576iSMPTE 344MED-SDI Mbit/s480p, 576pSMPTE 292MHD-SDI.485 Gbit/s, and 1.485/1.001 Gbit/s720p, iSMPTE 372MDual Link HD-SDI.970 Gbit/s, and 2.970/1.001 Gbit/sp60SMPTE 424M3G-SDI.970 Gbit/s, and 2.970/1.001 Gbit/sp60SMPTE ST-G-SDI Gbit/sp30SMPTE ST-G-SDI Gbit/sp60SMPTE ST-G-SDI Gbit/sp/4k@120,8k@60NA48G-SDINA48 Gbit/sp/8k@120,8k@60Table 1: SDI Standards List

What is SD-SDI?

The SD-SDI standard supports the 270 Mb/s bit rate. SD-SDI transmits low-resolution PAL-compatible video 720 * 576 @ 25fps and uses a clock rate of 27 MHz.

In , ITU-R (formerly International Radio Consultative Committee) released Recommendation BT.656-2, incorporating the new serial digital interface defined in EBU Tech. and SMPTE 259M.

This interface 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), the SD-SDI standard, was defined as today&#;s serial digital interface.

What is HD-SDI&#;

The HD Serial Digital Interface (HD-SDI) standard is standardized in SMPTE 292M. Although this standard is known as the 1.5 Gb/s interface, it supports bit rates of 1.485 Gb/s and 1.485 / 1.001 Gb/s.

HD-SDI is widely used in high-definition surveillance. It is unique in its ability to provide high-definition video at a resolution of p at a frame rate of 25 or 30 while retaining all the video details with a latency almost equal to that of analog systems.

OPTCORE provides a comprehensive line of HD-SDI SFP transceivers for particular surveillance applications.

What is Dual Link HD-SDI&#;

Dual Link HD-SDI is a new standard introduced by SMPTE 372M in . It is an enhanced version of HD-SDI, supporting a higher speed of 2.97 Gb/s through dual links. This standard suits high fidelity and resolution applications like digital cinema and HDTV P.

What is 3G-SDI&#;

This standard is 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 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 CRC generation, checking, line number insertion, and capture.

The 3G-SDI standard has been widely used in the broadcasting industry, and many manufacturers can provide related products. At the same time, as the security industry continues to develop, the advantages of high-speed, uncompressed digital are gradually being explored.

The suppliers have launched many 3G-SDI series products, including optical transceivers, conversion equipment, digital switching matrix equipment, and splitters. These devices adopt 3G-SDI signals and are also backward compatible with 1.5G signals for long-distance transmission to meet users&#; diversified needs.

What is 6G-SDI&#;

6G-SDI standard defines a bit-serial data structure, electrical signal, and coaxial cable interface for transporting signals with a total payload of 5.940 Gb/s or 5.940/1.001 Gb/s. This standard also specifies coaxial cables and connectors&#; electrical and physical characteristics.

This standard defines several mapping modes for carrying -line and -line image formats and associated ancillary data into a Single-link 6 Gb/s [nominal] SDI bit-serial interface.

What is 12G-SDI&#;

The 12G-SDI is a serial digital interface standard developed to support higher resolution, frame rate, and color fidelity. It provides four times the bandwidth of 3G-SDI, carrying 12Gbps, making it ideal for the 4K 60p format.

This is not new. UG has been developed 6G / 12G since but has not been approved by the standard governing body SMPTE (Society of Motion Picture and Television Engineers) under the SMPTE ST- draft name.

ShieldRock Quad 12G-SDI Optical Extender (Image source: B&H)

Most 4K professional cameras, medical endoscopes, and monitors use four BNC connectors simultaneously transmitting 12G-SDI signals. As technology advances, some cameras, such as the Sony PXW-Z280 handheld all-in-one camera, now include 12G-SDI output connectors; nevertheless, only one SDI cable meets the 12G transmission standard and can directly transport 4K 60p signals.

Some video transceiver suppliers also launched 12G-SDI transceivers to meet the higher resolution television and broadcast market usage.

What is 24G-SDI&#;

24G-SDI also known as UHD-2 or 24G UHD-SDI, defined in SMPTE ST-, this standard supports 8k 120p resolution. It is the latest generation of serial digital interfaces for targeted UHDTV real-time streaming media interface applications. 24G-SDI uses eight lines of SMPTE ST , allowing video signals to be transferred at speeds of up to 24 Gbps.

What is 48G-SDI&#;

48G-SDI is a new term some industry leaders propose but has not been defined in SMPTE. By mixing four independent 12G-SDI channels, 48G-SDI supports an 8K (48G) signal over fiber cable. It is ideal for transmitting multiple uncompressed SDI streams or 8K broadcast-grade UHD signals.

History of serial digital interface (SDI)

In , the former CCIR issued CCIR 601 based on the institutional proposals of the European Broadcasting Union (EBU) and the American Society of Motion Picture and Television Engineers (SMPTE). At a sampling frequency of 13.5 MHz, 8-Bit quantification and 4: 2: 2 chrominance sub-sampling unify the digital parameters of both 525/60 and 625/50 television scanning systems.

In , CCIR became the International Telecommunication Union Radio Telecommunication Sector (ITU-R).

In , CCIR released CCIR 656, based on the EBU Tech. and SMPTE 125 standards, and proposed a parallel interface that transmits CCIR 601 specifications using 11 twisted pairs and 25-pin D-type connectors.

Some early digital devices used this interface. Still, because of the short transmission distance, the connection is complicated and, for other reasons, not suitable for large-scale use.

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The CCIR 656 also includes the EBU Tech. serial digital interface standard, which EBU proposed in . This standard uses 8/9 block coding at a bit rate of 243 Mb / s but only supports 8-bit quantization, and it is not easy to design a stable, cheap interface chip.

In , ITU-R released Recommendation BT.656-2, incorporating a new serial digital interface defined in EBU Tech. and SMPTE 259M. This interface uses a 10-bit transmission and NRZI encoding. The clock rate is 270 Mb / s when transmitting a 4: 2: 2 level signal from ITU-R BT&#;601 (part A), now the famous SDI.

Using a 75-ohm coaxial cable and 75-ohm BNC connector (IEC -8) enabled the reuse of many existing cabling inside the station in a digitized system, and SDI became standard on digital devices. This is based on the final realization of the studio, master, and broadcast control system of digital.

China also formulated the corresponding national standard BG / T concerning the above standards. EBU Tech., SMPTE RP145, and ITU-R BT .799 propose dual-link to meet the demand for high-quality program production for the 4: 4: 4 level image and chroma key of ITU-R BT.601 (Part A) Concept that transmits both the R&#;G&#;B &#;/4: 4 image and the other broadband signal over two SDI channels at the same time.

In , with the release of Recommendation ITU-R BT.709, the accelerated development of high-definition television technology, the use of a serial digital interface to transmit high-definition signals has been agreed upon in the industry, for which SMPTE defined in the 292M standard clock frequency up to 1 The serial digital interface of 5 Gb / s level, the corresponding international standard is ITU-R BT. , this is the well-known HD-SDI.

In , the ITU-R specified a 2.97 Gb / s serial interface in BT.-6, which still uses the 75-ohm coaxial cable and the IEC -8 standard connector. In addition, SMPTE 424M also gives a similar definition of a 3 Gb / s level interface. The advent of the 3 Gb / s serial interface solves the previous need for dual-link HD-SDI, such as 4: 4: 4 / 12bit or p50 / 59.94 format programming.

Manufacturers have introduced 3 Gb / s serial interface chip products. However, copper is somewhat powerless in some situations that require long-distance transmission, such as connecting two distant studios.

Currently, optical fiber cable has become a natural substitute for copper. ITU-R BT. and SMPTE 297M are standards for transmitting serial digital signals over optical fiber cables. Take ITU-R BT. as an example. Only single-mode optical fibers and corresponding optical connectors are allowed when transmitting high-definition signals &#; Electrical, electrical-optical conversion by the appropriate optical receiver and optical transmitter to complete.

SD-SDI vs. HD-SDI vs. 3G-SDI, what is the difference?

The primary electrical specifications of HD-SDI and SD-SDI are the same, but the transmission bit rate is much higher than that of SD-SDI.

Since the ITU-R BT.-2 specifies that the luminance sampling frequency of high-definition video signals is 74.25 MHz and the sampling frequency of two color difference signals is 37.125 MHz respectively, the primary bit rate of HD-SDI reaches 1.485 Gb/s.

The distribution of high-frequency transmission cable parameters affects the transmission of high-definition video signals, so the cable length will be significantly reduced.

The data transmission format of HD-SDI is the same as the transmission format of SD-SDI, and the luminance signal Y and the color difference signals Cb and Cr subjected to time-division multiplexing are handled as 20-bit words. Each 20-bit word corresponds to a color difference sample and a luminance sample. The multiplexing modes are (Cb1Y1), (Cr1Y2), (Cb3Y3), and (Cr3, Y4).

With the advent of high-definition (HD) video standards such as i and 720P, interfaces have been adapted to handle higher 1.485Gbps data rates. The 1.485-Gbps serial interface, commonly called the HD-SDI interface, is defined by the SMPTE292M.

It uses the same 75-ohm coaxial cable. SMPTE approved the new standard, SMPTE424M, which doubles the SDI data rate to 2.97Gbps over the same 75-ohm coaxial cable and supports higher-resolution images such as P and digital cinema.

3G-SDI is an upgraded version of HD-SDI. The system supports SMPTE424M, SMPTE292M, SMPTE259M, SMPTE297M, SMPTE305M, and SMPTE310M standards.

What are the SDI Advantages?

• High Reliability: SDI transmits video data without compression, resulting in a high-definition multimedia interface.
• Latency-free: The SDI signal is transported through coaxial cables, delivering clear HD images without delay and uncompressed digital signals. This is crucial for real-time signal transport, such as monitoring and live broadcasts.
• Long-distance: compared with traditional technology, the serial digital interface supports tens of transmission kilometers over fiber cable without degrading signal quality.
• Maximum cabling: Most SDI utilize the BNC connector, which is compatible with analog cabling. Hence, you may upgrade the existing system to SDI without significant modification, cutting the total cost.

SDI Devices

There are many SDI devices for broadcast, post-production, and AV industry applications, but the primary devices include the following.

SDI Converter

The SDI converter is one of the most used devices for video and broadcast engineering applications. It usually converts the SDI video signal to the HDMI interface. The user can connect the computer&#;s HDMI outputs to high-end SDI equipment using this converter.

SDI Extender

Generally, we call the SDI to fiber converter an SDI extender. Unlike the standard SDI to HDMI converter, this extender has one or multiple fiber ports to connect with single-mode or multimode fiber cabling systems. Fiber technology provides an extended transmission distance of 2km, 10km, or 40km.

SDI Distributor

An SDI distributor is a device that takes a single SDI input (SD-, HD-, 3G&#;or 6G-SDI) with multiple outputs and distributes a single SDI signal to multiple SDI devices simultaneously. The distributor is ideal for Broadcast Studios&#; Live Events and Post-Production applications.

FAQs

Q: What is 8K?

A: 8K is a generic name for a video resolution ×. It has a 16:9 aspect ratio and 33,177,600 pixels. The more precise word for broadcast and live event demands is UltraHD2.

Q: What are the factors that affect the stability of an SDI system?

A: The main factors are a stable power supply, good impedance matching, the reduced effect of distributed capacitance, suitable connectors, and the cable&#;s shielding characteristics.

Q: Does SDI carry HDCP?

A: No, it doesn&#;t support HDCP, so converting HDMI to SDI won&#;t carry HDCP.

Q: Is SDI better than HDMI?

A: It depends on your streaming situation. If you run the cable over long distances, it is better to use SDI, but HDMI will be the most economical choice for a very short distance.

Q: Does 3G SDI support 4K?

A: No, 3G-SDI does not support 4K resolution. Since it only supports p,
You should use 6G- or 12G-SDI for HD video for a 4K signal.

Q: What is SDTI?

A: SDTI stands for Serial Data Transport Interface. It is a protocol standard for transporting compressed video streams over the SDI (Serial Digital Interface) line. This includes DVCPRO, DVCPRO 50, Betacam SX, Digital-S, DVCAM, and MPEG-2 formats. SDTI was developed to exchange digital audio and video signals in their original compressed formats rather than uncompressed and recompressed formats.

Final Thoughts

This guide has provided a comprehensive introduction to the SDI terms. Technological advancements have made the serial digital interface ideal for high-resolution broadcast streaming and monitor transmission. Once you understand the differences between SD, HD, 3G, 6G, 12G, and 24G-SDI, you can choose the best solution for your application.

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