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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.


VGA is capable of resolutions above 1920x1080, but I seldom see this specific resolution and aspect ratio used by A/V companies that I am asked to work with. One of the reasons is that up until the recent release of Microsoft Office 365, PowerPoint defaulted to 4:3 aspect ratio slides and A/V companies have invested both in 4:3 native hardware and equipment. So with clients continuing to produce slides in this aspect ratio and slow demand to go widescreen, A/V companies have been equally reluctant to upgrade equipment.

Now clients and webcasters are demanding widescreen but unfortunately many A/V companies still utilize equipment that doesn’t support native 1920x1080. This inability to send 1920x1080 video signals might be due to a VGA distribution amplifier that is limited to a max resolution of 1650x1050 or the use of similar but different aspect ratios like 16:10 (1920x1200).

If your video switcher has a VGA or DVD-I input, it likely has a built-in scaler. But if it doesn’t, you will need to add one to your workflow or your switcher may not be able to see your video input. A scaler won’t fix aspect ratio issues but it will increase the size of the image to fill the screen, or at least until either the vertical or horizontal fits the screen when a different aspect ratio from the 16:9 video aspect ratio is used. I general I would not suggest stretching the image to fit, if you are presented with that option, because you will end up stretching or squishing the image.

Both of the previously mentioned converters have internal scalers, but if you need to scale an HDMI output you will want to look at an Up/Down/Cross converter. Both Aja and Blackmagic Design make popular models.

Distribution Amplifier

Splitting a signal from one input to multiple outputs is required when you need to connect a single computer to multiple devices, like a projector/presentation switcher and video switcher. You never want to use a passive splitter as this can result in signal loss. A powered active distribution amplifier acts to amplify and split the signal so that it does not suffer or drop out when you need it most.

If you’re adding a VGA distribution amplifier (or even a VGA switch to manually switch between multiple VGA inputs when more than one computer is connected), make sure it supports 1920x1080 and that you send it a 1920x1080 video signal. If it doesn’t support this aspect ratio, then using a 16:9 aspect ratio signal, like 1280x720, will deliver the best results when scaling, avoiding annoying black bars on the top and bottom or sides.

If an HDMI output is used, then a professional HDMI distribution amplifier (Figure 5, below) is what you need. All HDMI DAs are not created equal, so I am in the process of replacing my old one that produced a fuzzy image to a KanexPro 1x2 model for $50 that reviewed well.

Figure 5. HDMI Distribution Amplifier. Click the image to see it at full size.

For HD-SDI distribution, I use the industry standard AJA 3GDA 1x6 distribution amplifier (Figure 6, below), which sells for $400. Be careful when comparing models because 3G HD-SDI supports progressive 1920x1080 frame rates (30P and 60P), while lower-cost models support only 1.5G HD-SDI, which is limited to interlaced 1920x1080 video.

Figure 6. 3G HD-SDI Distribution Amplifier. Click the image to see it at full size.

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