DENVER -- Cable Next-Gen Technologies & Strategies -- It's been almost two years since Comcast promised to launch its 4K UHD and HDR set-tops, yet as the first quarter of 2017 rolls to an end, those boxes are still missing in action. The question is why, and specifically, why Comcast would have marketed 4K so early without being able to deliver the set-tops necessary to make it work in most homes.

Comcast Corp. (Nasdaq: CMCSA, CMCSK)'s Joshua Seiden, executive director at Comcast Innovation Labs, offers some answers in his recounting of the company's requirements for Ultra-HD video delivery. And those requirements are significant. Comcast doesn't just want to offer a 4K UHD service, it wants that service to include high dynamic range (HDR) technology and 10 bit HEVC encoding for greater color precision. (See TV's Paradox: No HDR Without 4K.)

Figure 1: Comcast's Joshua Seiden spoke at a breakfast session during Light Reading Cable Next-Gen Technologies event. Moderator Alan Breznick is on the left above, followed by Seiden, Layer3 TV's David Rapson, Verimatrix CEO Tom Munro and SCTE/ISBE's Niem Dang.

"4K for us will always go with HDR," says Seiden, contradicting earlier Comcast plans that called for launching a 4K-only set-top followed by an HDR box. Seiden adds that Comcast also made the decision to implement 10 bit HEVC in order to deliver a premium experience with the highest possible quality of color rendering. (See Comcast to Launch 4K Set-Top Later This Year.)

The problem is that serious HDR development didn’t get underway until a few years ago, and 10-bit HEVC is new enough that Comcast is having trouble getting the decoders it needs for its set-top boxes. Seiden notes that the workflow requirements for processing UHD content are also complex because Comcast is taking the highest-quality source material from its programmers and doing the transcoding and other preparation itself before making that content available.

In short, UHD TV has evolved quickly, and as a cable operator on the bleeding edge of development, Comcast has found itself adjusting its expectations for service quality as the technology has improved.

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Comcast's plans appear to have changed in other ways as well. Although Comcast has shown demos of 4K UHD video over both QAM and IP networks, Seiden says that he sees the company moving forward solely with 4K over IP. (See Comcast Shows Off Rio in HDR... in Philly.)

"4K HEVC almost has to be done over IP," declares Seiden, pointing out that a single 4K stream takes up almost an entire 6MHz channel in a cable network, and with QAM resources as tight as they are, that's too much bandwidth for an operator to siphon away from other operations.

Of course, over-the-top companies like Amazon.com Inc. (Nasdaq: AMZN) and Netflix Inc. (Nasdaq: NFLX) long ago committed to IP for 4K, and every other kind of video delivery. But cable operators haven't been as clear on their strategy because of their existing QAM-based systems. If Comcast truly is planning to launch 4K to the masses solely over IP, that decision also speaks to the company's commitment to transitioning many more of its customers to IP video delivery.

As for timing, the wait for Comcast's 4K UHD services may finally be coming closer to an end. According to Seiden, the company has multiple 4K set-tops in the works, but the first ones should arrive in 2017. Comcast will likely target serious 4K TV promotions nearer to the start of the 2018 Winter Olympics.

— Mari Silbey, Senior Editor, Cable/Video, Light Reading