HD Webcast Production: Choosing Video Scalers and Converters
In this ongoing Streaming Media Producer series on webcast video production, Shawn Lam covers the video format converters he uses in his own HD webcast workflows, and one new converter that just might be the video converter, scaler, and distribution amplifier to rule them all.
My life would be so easy if every camera and laptop that I need to connect to my video switcher had multiple live outputs and could support the 1920x1080 30P resolution and frame rate that I prefer to use--and included in these multiple outputs is the professional connection standard of 3G HD-SDI. But this isn’t the case and will never be; laptops don’t offer HD-SDI outputs. So in order to connect the variety of input devices that are common in the webcasts that I produce, I rely on a variety of video format converters, scalers, and distribution amplifiers (DA). For simplicity I am going to assume that the video switcher you are using is a digital video switcher primarily designed for HDMI and/or HD-SDI video inputs, and not an HD analog video switcher, or either a digital or analog SD video switcher.
The need for converters, scalers, or DAs depends largely on the type, number, and resolution of the video outputs from the devices (camera and computer) that you are trying to connect and the devices that you are connecting to. The most basic setup would be a single camera connecting to your webcast encoder using an HD-SDI cable but the moment you add either an additional camera angle or computer input, you need to add a video switcher and possibly one or several converters, scalers, or DAs.
Simple Video Format Converters
Some video switchers have internal video format scan converters, and hence can accept a wider variety of inputs. Increasing available video inputs from HDMI or HD-SDI to include VGA solves the most common connection challenge that webcasters are faced with. Unfortunately, A/V companies still default to using VGA cables to connect laptops to projectors and laptops to presentation video switchers that connect to projectors.
One reason is that VGA cables (and the equivalent 3- or 5-wire group of composite cables with BNC connectors--see Figure 1 below) can run longer than digital DVI or HDMI cables; the other is because these companies are primarily catering to their clients’ needs for displaying computer inputs on projection screens, and adding a webcast output is an afterthought, which means it’s the problem of the video production company doing the webcasting.
Figure 1. A simple VGA-to-3-component cable converter is often used with presentation video switchers but with both video signals being analog, they require a scan converter before the cable can be used with a digital video switcher.
Few digital HD video switchers have native VGA inputs, but don’t assume that this means they can’t easily accept a VGA input. The DVI connector comes in three flavors: DVI-D, DVI-A, and DVI-I. The -D version is digital only and can be converted to and from an HDMI connector with a simple converter, albeit without any audio that might be embedded in the HDMI cable. The -A version is analog-only and can be converted to and from VGA with a simple converter. And finally, the -I version is Integrated, which means it can be converted to both VGA and HDMI with the appropriate converter.
All of these converters (Figure 2, below) are simple passive converters that you can buy for a few dollars and don’t convert the signal, but rather remap the connection pins of one format to the connection pins of the other. What all this means is that if your video switcher has either a VGA, DVI-A, or DVI-I, input you can input a VGA input.
Figure 2. VGA-to-DVI (top) and HDMI-to-DVI (bottom) converters.
Now don’t assume that because the laptop you want to connect to has an HDMI output that you can avoid VGA altogether, because often the laptop output is first routed to a presentation switcher (a video switcher that powers the video screens) and this switcher and/or the distance between the switcher and the input laptop might be the reason VGA is the format that you are given. Also don’t ignore the fact that often you can’t connect your video switcher directly to the laptop used for presentations, because the laptop output is also required for the projector or the presentation switcher so that it can power the projector.
Ethernet Doesn’t Always Work
Some video switchers have LAN (Ethernet)-connected solutions with names like iVGA or Desktop Presenter, but these solutions require you to install software on the presenters’ laptops, and additionally may require the laptop to have a Windows OS. This solution isn’t practical in my workflow. In my experience, some clients lack the necessary admin privileges to install software on their laptop, and installing software on each presenter’s laptop at a conference with new presenters on an hourly basis increases the odds you will run into a problem, most likely with the presenters who need to use their own laptop to access specific software or access a corporate network.
These solutions also don’t work well when a presentation switcher enters the workflow, as you can’t connect Ethernet to these switchers. Often, presentation switchers are required when you are working with multiple computer inputs, even if the second one is only for a holding slide.
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