Whatever happened to SDI?

John Mailhot, CTO networking and infrastructure at Imagine Communications, takes a look at the so-called war between SDI and IP

By Contributor

Published: April 15, 2021

John Mailhot, CTO networking and infrastructure at Imagine Communications, takes a look at the so-called war between SDI and IP

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Four or five years ago, an exhibitor at IBC booked a lot of poster spaces for a sticker that read, in very large letters, SDI must die . Well, that is one view.

SDI is an incredibly successful interconnection technology. It has been adopted universally for digital video, and - within its limitations - it works very well indeed. It has served the industry for more than 30 years and has evolved over that time with a 40X increase in capacity.

Because of this, there is a vast wealth of equipment installed in production and delivery facilities around the world, which talks to other pieces of equipment through these one-signal-per-wire coaxial SDI cables. SDI equipment works.

Establishing the ground rules Throughout my long career in broadcast, I have learned one universal truth: If a piece of equipment still has an ounce of life left in it, a broadcast engineer will not throw it out. SDI hardware - and SDI itself - still works.

So, my first point is that, despite what some might say, we are not facing a war between the old guard of SDI and the new kids doing IP. Those kinds of words are attention-grabbers on the walls of busy convention centres, but this is not the reality on the ground. It is now the time for the right conversation, about how SDI and IP fit into our future plans.

The second point I make anytime I can is that while sometimes we use the term IP for convenience, what I really mean is equipment and architectures conforming to the SMPTE ST 2110 standard, and more broadly the AIMS roadmap. As the editor of the standard within SMPTE during its development, I am personally committed to ST 2110. But ST 2110 is the future because it is an agreed standard that the industry has comprehensively backed, and it has been proven through hundreds of high-profile projects.

The media infrastructure evolution So, if SDI works, what drives a need for IP/2110 in media infrastructures? It is an enabling technology: a new tool for doing things that stretched the bounds of SDI historically.

I noted earlier that SDI works well within its limitations. By that I mean it handles signals up to HD (1080p) very well, with excellent cable reach and plenty of fibre options. Beyond that, there are limitations - 12G SDI for UHD is a great interconnection within a rack or a flypack, but the reach is a bit shy for a big facility. Additionally, the scalability of 12G SDI routing systems is limiting for a large facility. As content production and distribution evolves into UHD and HDR at scale, SDI will not do it for us or only with problematic workarounds.

The nature of SDI crosspoint routing has some built-in breakpoints. If you have designed a system around, say, a 288 x 288 SDI router, then as sure as the sun rises in the morning, someone will discover a pressing need for a 289th source. Once again you are facing workarounds and production limitations. Then someone will need a 290th source, and so on. Meetings are held and shouting matches happen over the allocation of router ports in an SDI facility.

One of the widely acclaimed benefits of SDI is that it carries audio embedded in it, so it stays together and stays in sync which is fine in parts of the media workflow where the audio is actually tightly bound to the video. But in production, the audio is just as often produced separately, and then re-united with the video right at the end of the chain. So in the production workflow, you have to add a stage that pulls the audio streams out of the video, maps them into (typically) MADI transport and takes them out to the audio room. Mixing and merging alongside all the other audio processes happens there, and then back through MADI to re-embed the audio streams (hopefully still in sync and only a little bit late) in every place where you need to hand off video with audio.

The complexity of embedders and de-embedders - their care, feeding and constant tweaking of delays - is the reality of daily life in production today. It's a source of unnecessary complexity that translates into errors and scaling challenges.

Real estate economicsSDI with embedded audio is clearly the evil we know, but it's still sometimes nefarious. When do we need to think about changing up? Where does the conversation around IP start?

The decision to build out new facilities from scratch at greenfield sites is often driven by real estate economics, workforce considerations, and other non-technical factors. Today, there are many new, large-scale production and delivery facilities around the world designed to operate at a scale and interconnectedness that would have been unthinkable with SDI alone. Even the typical new large OB trucks being built today have staggering numbers of sources and destinations and a need to support UHD and HDR requirements that push well past the limitations of SDI.

If you are starting with a blank sheet of paper, like these projects did, then you have to consider what will and could happen in the future. Consumer transmission of UHD, for example, feels a long way away - until it's not. But just like the early days of HD (while consumers were still viewing 99 per cent of content in SD), UHD for production is here today, with the collateral benefits of higher resolution, improved gamut and HDR. Producing in UHD and HDR makes a better original, even if the distribution is only HD. Content produced in UHD and HDR today will have a longer repurposing life, into more formats than HD, while looking better getting there.

LINK:	https://www.tvbeurope.com/ip-migration/whatever-happened-to-sdi...
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