Pro AV Logo Originally published as a Consultant's Connection
column in Pro AV Magazine
  April 2005

Can We Skip DVI And HDMI?

DVI and HDMI present new challenges in designing AV presentation systems. How hard does it have to become before we go all the way into IP network-based video systems for pro AV?

By Tim Cape, CTS-D

All it takes is one look at the dizzying array of available video source formats, delivery formats, and display formats to get a sense of the complexity we're often faced with in a typical pro AV project. Sometimes we have to do a lot of mixing, matching, processing, scaling up, converting down, routing, and switching to make a video system do what we want it to do. We have to determine the video formats of the sources, find a display that will provide the image size, quality and brightness we need, and then figure out how to get all the sources to all the displays. Determining the sources and choosing the displays is easy. It's getting signals from all those sources to those displays that's the hard part.

It used to be so simple

In the past, the problem was relatively uncomplicated, at least before there was much computer video. For a pre-PC pro AV system, we may have had some composite and S-video to route. Perhaps there would be a slide projector that might run on it's own or even make use of a slide-to-composite video converter.

Starting with NTSC in 1953, followed later by PAL and SECAM, coaxial cable carried video. Life was simple, and configuring a pro AV system in the old days was easy. We had more trouble with displaying the video than transporting it from source to display. Then came S-video, which required another conductor. Next came RGB, which required another conductor (or three), and later component in its various flavors, which is where we seemed to have stalled in terms of getting analog video from place to place. The conductors sometimes changed to twisted pairs instead of coax as we tried to get higher resolutions to go farther down a smaller diameter pathway. We added colors, raised resolutions, and changed aspect ratios, but the underlying electrical formats remained the same. Then came digital.


Sure, digital source formats could be transported on the old analog delivery wiring if we converted the signal, but we lost quality, at least in theory, so we had to start moving digital bits and bytes instead of analog color and contrast. This is when I realized that as much as we feel like we're pushing forward in the AV industry, we're fundamentally reactive. We're pushing ahead to get audio to play and video to display for a bunch of people in a room in a better way, and then someone comes in with a computer that only has a DVI output connector.

Sometimes we're reacting to the broadcast industry. They ask, “can't we run HD-SDI to the projector?” Other times it's the desktop computer industry. “I can connect DVI to my desktop monitor. Why can't I run it up to the projector in the ceiling?” It comes from the home theater market, too. “I'm using HDMI at home, why can't you pro people display it on your fancy AV system?” We're not really creating anything they have to deal with, except limitations. They're pushing us. But we can make them look very good when we get it right.

Tunnel vision

Part of the problem is that the signals we're being asked to accommodate were created for reasons other than switching and routing in pro AV systems. Most of what we're asked to accommodate was developed with a source and display or two in mind — all within a few feet of each other. The creators of these problems aren't really thinking about routing and switching multiple sources to multiple displays that have hundreds of feet of cable between them.

They certainly weren't thinking about this with digital visual interface (DVI) and high-definition multimedia interface (HDMI). On top of the fact that the video signal gives up after about 16 feet or so, there's copy protection in the form of high-bandwidth digital content protection (HDCP) to deal with, which introduces additional display limitations and significant authentication delays to content that used to travel blissfully down the coax to the display. What were they thinking? I have an idea, but I'm pretty sure it wasn't about what we need to do with the signal in a presentation environment.

Regardless of any thinking or lack thereof, we seem to be getting pushed against the system design wall between rising resolutions and new digital formats with copy protection. We may be able to get a great high-resolution analog video signal to go 250 feet with our eyes closed, but we can't get a new digital signal past 16 feet without some finagling at the moment, much less route and switch it. So we go back to the drawing board, which we really haven't left because we're still trying to make the last format look better and go farther.

So now what?

We're in a bit of a pickle. We need to support our customers, but transcending the laws of physics (like some consumer audio seems to be already) is not quite our field yet. Are optical fiber networks the answer? Are they viable for pro AV? It looks like we need to do what we've always done — see what cables and little boxes can be manufactured to make the end-user's new toys work in the context of a presentation or videoconferencing system. But there's only so much we can do, and it's getting harder to do it.

What this means is that for the manufacturers of little video boxes that can almost magically extend, convert, and transform the new video formats into something useful, there are more products to release and sell — at least for a while. It also means that analog video may continue to live a little longer than it might have otherwise because dealing with digital formats that were designed for desktop or home theater systems are simply impractical or too expensive to be viable for many pro AV presentation systems.

Following this logic, it will also likely mean that storage, management, control, and delivery of high-resolution video over an IP network may become attractive enough to be a more common alternative to analog or current non-network digital video sooner rather than later. We have the technology for this to happen — almost.

There are still a lot of parameters that have to be just right for it to work at this stage. But perhaps at some point, we can leave HDMI for the desktop and use the network to deliver video instead. Maybe the network cloud that keeps showing up in AV system drawings really has a silver lining after all.


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