Switched on

Glitches in switching will ruin presentations, broadcasts and live events and there are various products on the market to ensure smooth transition. But for some applications sometimes smooth isn’t enough and only seamless switching will do. Anna Mitchell catches up with some of the manufacturers that provide the products that do just that.

"How do you define seamless switching?" Robert Drake, research and development manager at TV One asked me before our interview had even started. The role reversal caught me off guard as I struggled for an answer. But, as it turned out, Drake's question had raised a pertinent point.

Whilst some purists may have you believe true seamless switching is replacing one image with another without showing a black or frozen screen, most of the developers of switchers will give a slightly more generous definition.

In The Kramer Guide to Video, Audio and Presentation, Dr Joseph Kramer defines seamless switching as: “A process that allows replacing one image on screen with one from another source seamlessly, ie. Without creating visual interference or image breakdown. It can be done in the video world using frame synchronised sources and vertical interval switching, and in the presentation world by pre-synchronising video and data sources and switching them during the vertical interval. Another effective technology is performing the switch via a short black period.”

“In TV One’s world,” agrees Drake, “most of the time seamless switching goes through black and back out again glitch free, which is the important bit. Or we have cross fades which allows you to go from one source and fade it into another source.

“One method of seamless switching is via a cut,” he continues. “So you have one source which we freeze for a frame or so while you bring in the next source. The reason you normally have black is because you’ve got two sources coming in with only one route into the scaling system. So you fade your first source out to black. The scaler’s not taking any video in it’s just showing black until you switch your other source into the scaler and then that back up through black. Effectively you’ve got two trains going into one tunnel and one has got to give way. When you do a seamless switch with a cut all that happens is it freezes the last frame, so it’s not showing black, and brings in the next frame. Effectively it’s doing the same thing but instead of black you’ve got the last frame.”

Ezra Ozer, vice president of marketing at Kramer Electronics, explains: “Seamless switcher is a phrase that is used in many occasions but you need to understand that a true seamless switcher costs a lot of money. You will not find a lot of pure seamless switchers so there are other ways to overcome issues to provide 90 per cent of seamless switcher definition with much lower prices.”

Kramer has trademarked one method of switching virtually seamlessly called Fade-Thru-Black switching. “The viewer will see black for a split second and the picture will evolve inside,” says Ozer. “So image goes down, then black, then goes up. You won’t see any jumps in pictures, you won’t notice anything - it is like the blinking of an eye.”

In price terms, Ozer says the difference between the glitch free switchers and the true seamless switchers is like the difference between a Rolls Royce and a Mazda. Kramer offers Rolls Royce products in the shape of its VP-727 and VP-727XL. Both products have eight universal inputs on five BNCs with the VP-727XL boasting two HDMI inputs. On the output side, the VP-727XL offers programme and preview HDMI outputs, while the VP-727 provides DVI-D outputs for preview and programme. The switchers both provide true seamless switching and dual scaling.

Analog Way introduced a new switching product at June’s InfoComm show in Orlando, USA. Opus is a 12 input (4 of which are digital) seamless switcher that incorporates six layers and three active scalers and allows the display of up to two PIPs on a live background. Frank Facon, marketing and communication director, at the company explained: “We also included a video output card providing SD or HDTV formats in various signals from Composite Video to HD-SDI. Thanks to the video output, presentations can be recorded in broadcast quality. A T-Bar enables seamless transitions directly from the front panel and an integrated audio stereo switcher features SDI audio de-embedder.” According to Facon, the product is suitable for integration and rental and staging markets.

Back at TV One Drake cites the company’s 7000 and 700 series as examples of true cross-fading products. The C2-7110 is described as a two channel, 9-input video processor for live event or presentation environments. It is joined by the C2-700 which provides the same functions with a different front panel and is designed for applications that require restricted access to functions. The product is joined by the 7200 which provides the same functions with two SD/HD-SDI inputs and two SD/HD-SDI outputs. The C2-7310 is a dual channel eleven-input video-audio processor. In switcher mode all the 7000 series provide equally powerful program and preview channels which allow any function (such as next image, PIP, keying or logo) to be set up and previewed, independent of the program output. Transition from preview to program is by cut, dissolve or special effect. The 1T-C2-750 and C2-760 DVI scalers also offer true seamless switching with cross fade capability.

Jed Deame, vice-president of image processing at Barco, says the company’s DCS100, DCS200, ScreenPro-II and Encore presentation switchers all offer true seamless switching. “The DCS-100 and DCS-200 feature straightforward and simple operation making it ideal in live events, company boardrooms, hotel ballrooms, houses of worship and education and training facilities,” he explains. “The ScreenPro-II HD seamless switcher is a multi-layer video display system that combines seamless switching with a variety of flexible video effects. The Encore is a modular, scalable architecture that can support from 1 to 32 screens for a wide variety of applications.”

At Datavideo, Rob Opdebeek says he’s particularly excited about one of the company’s new switching products. The SE-2000 HD Digital Video Switcher offers five inputs with options covering HD-SDI and DVI-D. The product allows the user to switch seamlessly between video and audio sources and blend high-quality digital content, without external genlock, due to a built in time base corrector (TBC).

And, from Christie, the Vista URS-1608 accepts multiple sources in any format (analogue composite to digital 4K) and seamlessly routes these sources to eight user-configurable outputs, each of which can be independently configured for any analogue or digital output format. The universal routing switcher boasts 16 inputs that cover S-video, component analogue, HDSDI, SDI, and 3G SDI, progressive DVI and progressive RGBHV. The product performs the processing to match the source to the output, including scaling, aspect ratio, colour-space, and frame rate conversion repeats.

Deame tells me that major changes in interface standards have affected the development of switchers recently. “AV integrators have begun using Blu-Ray DVD players and other HDCP copy protected sources. In order to accommodate these sources the switchers need to be licensed for HDCP and incorporate this new technology into the products,” he explains.

He continues to say that in the future Display Port, a digital display interface, will be an important consideration for switcher manufacturers to accommodate. “Display Port is the next generation in AV interface technology. It enables much higher resolutions and bit depths (up to 16 bits per component). It also has a convenient locking connector and a DVI compatibility mode. Barco is active in the standards committees defining these new interfaces.”

Drake says he sees much of the future innovation in products centred on special effects. “There’s not really much you can do when you want to go from source A to source B, the main thing is to provide a very clean switch. However, on the effects side, I think in the future we’ll see more 3D type effects – maybe things whizzing off the screen, rotating off the screen.”

Many manufacturers offer a variety of innovative techniques for switching solutions that seem invisible to the naked eye. However, there are a few applications when switching must be seamless and there are some very powerful products on the market that provide this functionality. As the market moves forward manufacturers will have to be vigilant in keeping on top of new standards and maintaining compatibility.

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