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How to Choose Video Converters and Scalers for Live 4K and HD Production

Signal conversion is required in most live HD video productions, and this article will discuss how to convert modern and legacy video signals to the most common outputs required in modern HD and 4K broadcasts.

Choosing and Using Signal Converters

I often find a desired 1080/30p workflow can be foiled by a single camera being limited to 1080/60i, which causes the entire workflow to either have to be changed to 1080/60i or the signal needs to first be converted to a progressive signal using a 3:2 pulldown removal. My preference is always to avoid having to add additional converters into a workflow. They introduce an additional potential failure point, and signal conversion adds latency to the video signal.

But that doesn’t mean I don’t own and carry with me a variety of signal converters, because a converted signal that shows some artifacts and latency is better than no signal at all. My preferred HDMI to HD-SDI converters support 60i-to-30Pp pull-down, 3G HD-SDI output, and a second output that is either HDMI or HD-SDI. In most of my workflows I prefer A/C-powered units, but on occasion a smaller battery-powered unit comes in handy.

Alternatives to Standard Cables

There are also alternatives to running HDMI or HD-SDI cables between devices. For longer runs, you can use optical fiber to connect a pair of converters to and from an HDMI or HD-SDI signal to fiber and back.

Wireless transmission is also an option. I’ve incorporated wireless transmission successfully into sports shoots on a handheld camera, and where running cables could prove hazardous. As with most workflows, we’ve had to pay close attention to the supported resolution of these devices, as not all support 1080/30p or 1080/60p.

Analog RGB still has legacy applications, but unless you’re working with older equipment, you might be able to avoid having to work and convert that format. I avoid analog-to-digital signal conversion whenever I can; the conversion quality is never as good as with a digital-to-digital signal, and A/D conversion can add significant latency.

Working with Computer Signals

Up until this point, I’ve limited the scope of the conversation to video signals, but the reality is that working with video signals is easy compared to working with computer signals, let alone incorporating computer feeds into live presentation is a common component of live-switched and streamed productions. The most challenging workflow I run into is when I film conferences and presentations that involve computer presentations, such as PowerPoints, and I need to split a laptop signal so that I receive one signal and the projection system receives the other (Figure 3, below).

Figure 3. A video distribution amplifier for splitting a VGA signal from a computer

Starting with an HDMI (or similar DisplayPort or DVI-D) connection makes this process easier, but again you have to keep in mind that your video workflow and the projection workflow will be receiving a signal with the same resolution and frame rate. The desired resolutions from the presenter’s computer are 720p and 1080p—they’ll fill an HD video frame without any black bars, unless the presenter designed her PowerPoint with the older 4:3 template and it’s being projected in 4:3, which is still very common for conferences.

Inevitably, you’ll run into computers that aren’t capable of what you would assume is a fairly standard HD resolution, and this will require scaling the signal so that it is a compliant HD resolution. Some video switchers also have a hard time accepting computer HDMI signals, and this can be inconsistent between the same company’s similar models and from one firmware version to the next. So it’s always a good idea to have a backup or two.

Digital signals such as HDMI, DisplayPort, and DVI-D (the digital version of DVI) can be converted using a simple passive converter. Working with VGA and DVI-A (the analog version of DVI) requires a scan converter that is cable of converting an analog signal to a digital one. I find that when I work with VGA and DVI-A, the chances of my being able to receive an HD signal decreases, so my VGA-to-HDMI or HD-SDI converter has to be able to scan, convert, scale, and output a 1080 signal that plays nicely with my video switcher.

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