Sept. 1, 2020 - Funny, isn’t it? A year ago, colleagues in our industry were alternately embracing, rejecting, or arguing about the upward trend to 4K video. We debated what "4K" actually meant. We got out our calculators to see what flavor of "4K" signal we could pass through our existing HDMI infrastructure. We watched as display manufacturers began replacing Full HD displays with Ultra HD versions (the correct term, as these have a pixel resolution of 3840x2160 and aren’t really true 4K).
And we slapped our heads and groaned as display analysts warned us to get ready for 8K video, along with high dynamic range, wider color gamut, and higher frame rates. We read up on the latest versions of HDMI and DisplayPort and reviewed the press releases from standards organizations that touted the latest versions of high-efficiency codecs, such as the new Versatile Video Codec (VVC.)
What a difference 12 months and a pandemic make. Now, most of us are working from and learning at home, watching video on Zoom, GoToMeeting, WebEx, Teams, and other conferencing platforms. Some of the video looks decent; a lot of it is pretty awful. Much of that can be blamed on "smart" video codecs that use adaptive, variable streaming techniques and dynamic stream shaping to maximize video resolution based on available network speeds during any given time interval. (Audio is easy to deliver – even spatial sound requires just over 1 megabit per second to stream.)
Aside from consumers buying large Ultra HD televisions like there’s no tomorrow – perhaps to stream "Hamilton" in HDR – we’re not hearing much about 4K and 8K TV right now. 2020’s showcase event for 8K, the 2020 Tokyo Olympics, was pushed back a year. Major sports leagues have cobbled together short schedules to compete in mostly empty stadiums, and some have moved their teams to one or two "bubble" locations for round-robin playoffs to stay isolated from COVID-19 outbreaks. (It’s not working, in case you’re wondering.) They’re not concerned presently about producing anything using cutting-edge video.
Guess what? Pixel resolution isn’t our primary concern now. Bandwidth is, and it tends to be fixed, like the water pressure in a large hotel. If one or two people are taking a shower or flushing a toilet at any given time, there’s ample flow. But if every guest did either one at the same time - well, that "ample" water pressure would quickly reduce to a trickle.
Internet bandwidth works the same way, and right now, we have hundreds of millions of home-bound workers, students, online gamers, churches, and Netflix bingers all grabbing as much bandwidth as they can, often at the same time. To compensate, video streaming services and Internet service providers (ISPs) can "throttle" bandwidth if necessary – this was done early on in areas with stay-at-home orders as online users surged, pleasing no one.
Alternately, we can make decisions on our end to help maximize bandwidth. For conferencing, distance learning, online worship, government meetings, and other events that will attract large numbers of remote viewers, the focus should be on effective communication above all else. Consequently, we should select a video format that’s most bandwidth-friendly. And instead of going up in resolution, we might want to go down. (Heads up: We’re about to become a bit contrarian.)
We need to fill a 16:9 screen (or 16:10) for certain. And we want to show fine detail. Do we need a high frame rate? Only if moving objects are being shown, which is rarely the case with an online class or Web conference. The amount of motion in a worship service is also minimal, compared to an auto race or a basketball game.
Turns out, we do have a video format that’s very well-suited to the online world - 1280x720p HD. Yes, it is the lowest version of HD, and compared to Ultra HD with HDR, it looks more like our old standard-definition video systems. Even so, many TV networks use 720p as a baseline for broadcasting everything from scripted entertainment to live sports - and it doesn’t look half bad on large screens.
The minimum viewing distance for 720p is around eight feet for a 42-inch diagonal 720p screen. But you won’t find any of those today, and you’ll be hard-pressed to score a 42-inch 1080p TV, what with manufacturers switching to Ultra HD native resolution. Not to worry; the major TV brands have incorporated some pretty sophisticated picture scaling engines into their sets, which makes your 720p video look better than you might expect on that new 65-inch Ultra HD TV.
If you want to be really thrifty, consider that just about every display we watch today supports multiple frame rates, so we can easily stream 720p HD at 25/30 frames per second for greater efficiency, or 50/60 frames per second if motion is being shown.
With a 60 Hz refresh rate, our pixel clock is 74.25 MHz, and with 4:2:0 8-bit color, the total data rate is about 1.1 gigabit per second, uncompressed. A high-efficiency codec like H.264 can easily mash that down in the range of 3-5 megabits per second with some latency. Even slow residential broadband connections (such as one we tested recently at 8 Mb/s in rural Vermont) can accommodate that data rate.
We can hear the cries and squalling of purists now. "720p is an old HD format!" and "Once you’ve seen 4K video on a big screen, you’ll never turn back!" Well, keep in mind that many of remote workers, students, worshipers, and civic-minded citizens are watching on laptops, tablets and even smartphones. And despite record sales of large screen TVs this year, there are still quite a few smaller TV sets in use today, with "smaller" defined as 55 inches diagonally or less.
Recall what we said earlier about our priorities: Effective communication tops all else, especially pretty pictures. Given the crushing demand on Internet connectivity right now, you should set your output resolution to 1280x720 on streaming cameras wherever possible. 60p is fine, but 30p will use just ½ the bandwidth of 60p. (Ditto 25p and 50p).
When we finally reach the end of the pandemic tunnel – and we WILL reach it; it will just take a while – the debates about 4K and 8K can happily resume. You can set your streaming cameras back to Full HD output and not feel guilty. We can get back to worrying about data rates and juggling combinations of frame rates and color resolution to pass through whatever display interface we’re stuck with.
Perhaps by then, average broadband data rates will support full "4K" Web conferencing. Either that, or we’ll have codecs so efficient that they can pack down 8K video streams to 10 Mb/s or less with just a few frames of latency. (Hey – we can dream, can’t we?)