The bandwidth requirement for a full-fledged 4K video signal, including audio, is enormous — nearly 18 gigabits per second. Therefore, superior compression technology is required to transmit a 4K signal into the home with current Internet technology. Every tech giant is up against extreme limits to make 4K video the Next Big Thing, and compromises will be necessary.
Because a 4K stream is so demanding, some sleight of hand marketing will be necessary to convince customers that they're receiving full 4K video. It will be called "4K," but it may not be the real thing for awhile. Here's why.
The 4K Picture Basics
There are lots of engineering details in broadcast TV, and they can get complex. I'm going to cover just the basics here. The links I've provided below have many more details.
The transmission of a 4K signal for a picture at 4096 x 2160 at 60 fps, when combined with audio requires, a 4400 x 2250 x 60 frame. Plus, while each pixel requires 8 bits of color information for red, green and blue, the actual transcoding for HDMI 2.0 uses 10 bits per color. The resulting bandwidth from the video hardware to the display is:
4400 x 2250 x 60 Hz x 30 bits/pix = 17.82 Gbps (gigabits per second.)
That's enormous, and now we know why Thunderbolt 2, with a capability of 20 Gbps, or HDMI 2.0 with a capability of 18 Gbps is required to handle 4K on a local connection from a device to the display.
Next: Compression to the Rescue
Part 2 - Compression to the Rescue
In order to transmit such a video and audio stream on the Internet, there must be excellent compression technology. One of the latest is called High Efficiency Video Coding (HEVC), also known as H.265. It's the successor to the H.264/AVC technology we are familiar with. HEVC is about twice as good as H.264, and is capable of compression rates of 100:1, more or less..
In parallel, Google has proposed its own compression technology called VP9. It is a similar technology and is royalty free while HEVC's is low but non-zero. For a more technical comparison of HEVC versus VP9, see "H.265 vs VP9: 4K video codecs explained."
Sony 4K UHDTV
Using a 100:1 compression factor brings that awesome 17.82 Gbps down to 178 Mbps. That would be a respectable 4K audio and video stream. This number, 178 Mbps, is a number that might mean something to you in the context of your own ISP's broadband service, likely in the vicinity of 4 to 50 Mbps and averaging just under 10 Mbps in the U.S. as of early 2014.
The Technical Dilemma
The next part is where it gets tricky, and it's all about viewer perceptions, the capabilities of our Internet infrastructure, and some relaxed language when the term "4K" is used.
For starters, I asked Mr. Chris Heinonen, a Senior Editor with Secrets of Home Theater and Displays Editor at AnandTech about all this. In a recent article, he pointed out that a current-day Blu-ray disc, while capable of delivering 40 Mbps to its codec is, typically found to deliver 23-28 Mbps with a 24 fps movie. (I'll use 25 Mbps in my calculations.)
Backing off the maximum in the same fashion, based on what viewers are accustomed to, a 4K stream with four times the pixels would have to deliver only about 112 Mbps instead of 178 Mbps before it's decompressed and sent on its way to the display.
However, HEVC/H.265 is about twice as good as the H.264 codec used with Blu-ray discs, that brings us to about 56 Mbps for a visually acceptable 4K signal. Mr. Heinonen's number, using a slightly different compression computation, is close: 40-48 Mbps.
That's more or less the line in the sand for good 4K streaming.
Next: The Seduction
Part 3 - The Seduction
So now we're down from 17.8 Gbps to, a low of 40 and a high of 56 Mbps. What does Netflix say? Last fall, the Netflix CEO Reed Hastings said, according to Digital Trends, "consumers won’t need more than about 15 Mbps to stream 4K video files once the content is up and running on the site...."
What does Sony say? On its product page for its newly announced 4K TVs, Sony has a footnote that declares a requirement: "10 Mbps for HD streaming or 4K downloads, 20 Mbps for 4K Ultra HD streaming."
Why is Netflix suggesting 15 Mbps and Sony 20 Mbps when all the math says that a minimal 4K stream requires at least 40 Mbps? It's likely because the average American home is not ready to support a 40 Mbps service. (However, those who can afford a UHDTV these days can probably afford that higher rate, but there's no money in small customer numbers.)
Moving on, Mr. Heinonen points out in his article:
Netflix wants to use 1/3rd of that [40 Mbps] amount. So what is this going to mean? More artifacts in your image compared to a Blu-ray disc. Macroblocking, those large colored blocks you often see in shadows, will be even more common. Fine textures and facial details won’t be there. Gradients will show banding and other flaws. You might get some objects that are sharper due to the 4K resolution, but you’ll see far more flaws in the image as well.
I surmise, if the picture looks poorer than expected, the provider can always blame it on network congestion. On the UHDTV sales side, recommending anything more than a 20 Mbps wouldn't sell a lot of 4K TV sets. It's also why Sony downloads 4K content in the background at a modest 10 Mbps to its 4K Ultra HD Media Player for playback at a later time.
Sony 4K Player
Mr. Heinonen wrote me, "Netflix can say 15 Mbps, but the math just isn’t on their side. It’ll look better than what we have now [streaming], but it won’t look better than any physical media we have now [Blu-ray]." If what we get with 4K streaming doesn't, in fact, look substantially better than what we can get from a Blu-ray disc, then the industry might have a perception problem.
Don't Forget Data Caps
By and by, as our technology progresses, available bandwidth and data caps will rise. But it's helpful to remember that excessive viewing of a lot of 4K movies from, say, Netflix, could clash with current data caps. For example, this article suggests 28 GB total for a 90 minute 4K movie. That's higher than my own calculation, but it's in the ballpark. It depends on the quality of the signal, the data rate and the compression.
So while your nominal Comcast cap of 300 GB/month and AT&T's Uverse cap of 250 GB/month wouldn't be in severe jeopardy, one would have to keep an eye on things, from time to time, for a few years.
The Big Picture
The technical requirements for a 4K video and high quality audio stream are severe. State-of-the-art compression can barely bring that signal into the realm of U.S. households. Some further compromises are necessary along with some marketing finesse. Customers, in the early days, may pay for what's called 4K service, but our average U.S. infrastructure is not there in terms of delivering a pristine 4K signal.