Services Global Viewpoint – March 2020

Developing SDI

It’s fair to say that SDI has provided the broadcast industry with unprecedented infrastructure connectivity over the past thirty years, but as more broadcasters move into the world of IP, we should remind ourselves that SDI has not always been as stable as it is now.

SDI continues to evolve and progress. Back in 1989 the data-rates for SDI ranged between 177Mb/s and 270Mb/s. At the time, I remember this was a truly breath-taking speed, baseband video had a bandwidth of 6MHz and FM radio stations were in the 89MHz to 95MHz region. The fundamental frequency of SDI, even then, was three times the frequency of an FM radio station, and that’s without even considering the harmonics needed to reconstruct the data streams.

Fast forward thirty years and the data-rates have gone through the roof. SMPTE’s ST-2082 standards, using quad-link 12G-SDI can reach aggregated speeds of 48Gb/s. This facilitates 8Kp30 4:4:4 or 4Kp120 4:4:4, both with 12bit samples.

However, it’s worth remembering that SDI, especially in the early days, was not as easy to work with as it is now. SMPTE specifications were in their infancy and many vendors had started to do their own thing and provide proprietary solutions for audio insertion and metadata handling. They were far from interoperable.

This has all changed now and after reaching maturity, SDI has become a truly interoperable and incredibly stable system of connectivity.

IP’s greatest strengths are its flexibility and scalability. As IP is data agnostic, that is it doesn’t care whether its transporting video, audio or web page information, then we have the opportunity to mix and match different frame rates, video and audio formats, and any type of metadata.

We are in the early days of IP adoption and many engineers are continually finding new challenges when implementing IP installations, especially for the first time. But far from being despondent, looking to the future and realizing the potential for IP is key to building successful IP infrastructures.

Again, we should remember that IP is in the early days of adoption and we’re still developing the tools needed to do the job. One of the major advantages of IP is that it is software driven and any enterprising engineer has the opportunity to build their own tool kit. Relatively new programming languages such as Python make parsing of streams of data easy. I agree that this approach has its limitations as it may not facilitate real-time analysis, but it will certainly help engineers build and develop their own tool kits.

SDI is truly established as the industry method of signal exchange and connectivity. We’ve had over thirty years to iron out the bugs and make it as reliable as it is today, it still has its place and will be with us for many years to come. But IP is fast on its heels and its potential for scalability and flexibility is making it attractive for many broadcasters, and as our knowledge and understanding develops, then so will its ease of use.

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