What is a SDI Signal?

We have countless standards in the world of video transmission. SD, HD, 4K, 8K- the list is quite long and ever-evolving, with new standards being constantly added. So, how does SDI signal fit into all of these?

What is SDI Signal?

SDI or Serial Digital Interface has been the choice for great quality video broadcast and transmission since the 80s. Many professional video equipment and consumer products use SDI for transmitting uncompressed video.

The video interface was introduced by the Society of Motion Picture and Television Engineers (SMPTE). During the 1980s, it was widely used by TV broadcasters and film studios and carried embedded audio as well.

SDI signals rely on high-quality coaxial cables with physical BNC connectors. The cables generally come with Teflon insulation for better picture quality. Originally, SDI supported the transmission of digital video signals at 270Mbps.

SDI cables have evolved to support optic fiber. SDI optic fiber cables also feature ST and FC connectors.

Common SDI Video Formats

SDI has evolved with time to offer high-bit rate video transmission. Now you can even broadcast 8K content using an SDI signal.

Let’s explore the common SDI formats used in the industry.


SD or standard definition SDI was the early start for the digital video signal. SD-SDI has many formats like the popular Digitized NTSC (4FSC) format with a transfer rate of 143Mbps.

Another highly-used format is the Digitized PAL (4FSC), with a bandwidth of 177Mbps.

The other two early formats are Component ITU-R BT.601 and Component ITU-R BT.601 with 360Mbps data transfer capability.

Most of these variants support an aspect ratio of 4:3.


This is the Enhanced Definition format of SDI and can run a progressive resolution of 576p. The data transfer rate of ED-SDI is 540Mbps. You can also go for dual implementation at 270Mbps.


Increasing resolutions demanded SDI to evolve. As a result, we saw the introduction of High Definition SDI in 1998 to support 720p and 1080i video transmission.

HD-SDI offers a data transmission rate of 1.5Gbps and frame rates of 23.98 Hz, 29.97 Hz, and 59.94 Hz.

After a while, HD-SDI introduced a Dual Link format as the market adopted HD resolutions. Demand for higher bitrates was evident, so the HD-SDI increased the data transfer rate to 3Gbps.

Now HD-SDI signal was able to support progressive 1080p resolutions. It could also provide the foundation for faster 60 Hz frame rates.


3G-SDI increased the bandwidth of format to 3Gbps to meet the demands of high-resolution videos. SMPTE released the standard in 2006 but went for a revision in 2012.

The new standard retained the same name while it was made to match all the Dual Link HD-SDI format specifications.

However, you don’t need two cables, but only one to broadcast your video signals.


Video resolutions keep getting better with passing time. After a few years of 3G-SDI, 4K videos shot into fame.

SDI was able to support 4K signals at 30 frames per second by using four HD-SDI signals. Or, you could go for four 3G-SDI signals to achieve the same result, but at 60fps.

Naturally, none were too convenient for the TV and video industry.

As a result, the SMPTE introduced 6G-SDI to support 4K at 30fps over a single signal in 2015. It came with the capability to transfer 6Gbps signals for 4K at 60fps using a single or dual-link.

The SMPTE further defined the UHD and DCI standards. The UHD-TV supported resolutions of 3,840 x 2,160 pixels and became a popular format for TV broadcasting.

At the same time, the DCI or Digital Cinema Initiative format was for new-age movie formats for more viewing pleasure. DCI supports resolutions of 4,096 x 2,160 pixels.


This format came into the market along with 6G-SDI but went through a revision in 2018. The resulting format became capable of handling Standard Dynamic Range (SDR) and High Dynamic Range (HDR) video sources.

As the name suggests, 12G-SDI can transmit video signals at 12Gbps. It can broadcast 4K content at 60fps over a single signal and 8K at 30fps using dual signals.

Features of SDI

SDI has quite a few unique features that make it a suitable option for certain applications. Let’s take a look at them!


BNC connectors are physical connectors that come with locks. You can easily secure your connection by putting the lock in place for a snug connection.

On the other hand, many cables like the HDMI come without locks. You have a less secure connection and more chances of physical damage.

Optical Fiber

SDI cables can support optical fiber connectors. We all know optical fiber connections are far better than contemporary choices.

You can transmit high-resolution videos at higher frame rates over long distances using optic fiber.

Low Video Quality Loss

SDI signals offer better picture quality over long distances. Quality coaxial cables with BNC connectors enable SDI to carry HD signals across a distance of 300 feet.

That means you will be able to transmit 4K or 8K signals over long distances using optic fiber cables. Other interfaces are not able to support such long distances. You are going to experience a loss in picture quality.

Embedded Audio

Regular SDI interfaces can carry a maximum of 4 digital audio signals, apart from the video. Other video formats at that time didn’t have such capabilities.

With time, the support for audio signals increased to reach 16 for HD-SDI. The 3G-SDI can help you embed 32 digital audio signals.

No Content Protection Hassles

Content protection protocols like HDCP can create hassles. Your transmission may suffer a loss of speed and throw up connection issues. Your video source and video output need to be in perfect sync for such content protection protocols to act.

SDI has no HDCP headaches. You can connect your sources and enjoy your videos without any issues.

Final Thoughts

SDI signal is one of the popular formats for video transmission. It has evolved with time to support 4K and 8K formats and higher resolutions. The features of SDI often make it a better choice for professional broadcasters.

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