By Shawn Lam
As 4K video workflows move closer to the production mainstream, the progression of video standards from SD to 4K is important to understanding overall signal compatibility, which is critical for live video productions. Any workflow is only as strong as its weakest link. If you have to mix multiple video and computer inputs, and both record an archive and send a live stream video signal, you’re likely to find yourself working with a variety of video and computer resolutions, scan types, frame rates, and connections. When working with different signals, you might struggle to find a common signal. That is where converters and scalers come into play.
Managing Multiple Standards
Of course, my productions didn’t just jump from one SD standard to one HD standard overnight, and there is likewise more than one 4K standard. From 4:3 SD we moved to 16:9 SD (which had the same 720×480 resolution but changed the pixel aspect ratio from 0.9 to 1.2), then to 1440×1080 HDV, 1920×1080 60i HD, 1920×1080 25/30p HD, and finally to 1920×1080 50/60p HD. Sure, higher frame rates are available in HD, but they’re reserved mainly for high-speed acquisition.
UHD and 4K have a similar story, although I’m thankful that we don’t have to work with funny pixel aspect ratios or legacy interlaced video signals in the 4K world. On the acquisition side, DCI 4K is 4096×2160 and UHD is 3840×2160, but outside of productions destined for the big screen, UHD will be the widely adopted delivery resolution, and frame rates will be the standard 24p, 30/60p (NTSC countries), and 25/50p (PAL countries).
Matching Your Gear to Your Deliverables
I prefer cameras for a live production to be capable of putting out a 1080/30p signal for live switching and a 720/30p signal for webcasting. This preference is designed to match my current deliverables, but if I’m also sending a signal to the projector for IMAG, I often need to work with 1080/60p. Right off the bat you can see that having a professional video camera that allows you to select an output resolution and frame rate is critical to starting your workflow with a progressive video signal.
Prosumer and consumer video camera models often lack the ability to select different output signals, and older HD cameras are limited to 1080/60i signals. If I jump down the workflow path, I have to keep in mind that if I’m filming in 60p and want to webcast in 30p, I need to use hardware or software that supports translating video from one frame rate to another. Recently, I changed my webcast software because it lacked this very ability, and 720/60p was a higher frame rate than is practical for a webcast.
Depending on the capabilities of your video switcher, you might not be able to mix and match video signals. This means you’ll need to either use a common video signal or add a converter or scaler into your workflow to make sure your video switcher can see all your video inputs.
HDMI vs. HD-SDI
Let’s talk about video connections for a moment. HDMI and HD-SDI are the two most common HD connectors (Figure 1, below). HDMI is a consumer connection and can easily be pulled out, so as a rule I no longer buy video cameras that don’t have HD-SDI outputs that I can lock in. HDMI also behaves differently from HD-SDI, and so the connection and reconnection aren’t instantaneous. Every signal along the way—especially if you’re using an HDMI distribution amplifier—will cause a signal interruption and reconnect if one of the signals is unplugged.
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