23 TECHFEED 4K
Realistically though, latency has little to do with encoding or bandwidth. Even if you have reliable 40Mbps connections for 4K streaming latency, it is the segmentation and cache levels throughout the CDN which are responsible for 95% of all latency. “You can try to optimise that, but it gets much more di icult with higher bitrates to push the envelope,” says Carnahan. Harmonic’s Karra agrees, “In order to maintain a premium video quality and a quality of experience, content owners do not want to see their content being ‘squeezed’ too much. A balance needs to be found.” The introduction of high dynamic range, which is believed to make a greater perceptual di erence to image quality than upping the number of pixels, adds more complexity to the mix. It also consumes about 10% to 15% more bandwidth than encoding a standard dynamic range UHD signal, reckons Harmonic. And that’s before higher frame rates – useful for sports, and nigh on essential for computer gaming – are taken into consideration. experiment during the World Cup required viewers to have at least 40 megabits into the home to receive the full 3840 pixel resolution running at 50 frames-per-second. A bigger challenge was the support of mixed HDR combinations throughout the distribution chain. The BBC wanted to stream an HDR signal that would work on the widest range of displays possible, and not just the latest HDR-outfitted devices. Yet the host FIFA signal was produced with an arguably more premium experience in mind. “Implementing universal HDR support would be ideal but is not economically viable,” says Karra. “This is why chipset, decoding devices and TV manufacturers are generally only implementing a subset with specific flavours. Even when a single HDR type is being used, switching back and forth to UHD SDR or HD can be challenging.” Harmonic says it can solve this pain point by enabling automatic HDR conversions if necessary and thereby allowing service providers to normalise their distribution formats, despite the diversity of content formats. Then there’s the issue of whether 4K content works for smaller screens. You need to use either a connected TV or an OTT ALTERNATIVES The BBC’s live UHD HDR streaming
set-top box connected to the TV to truly benefit from the video quality increase in a perceptible manner. Yet the worldwide trend is toward increased mobile device viewing. In Akamai’s analysis of what constitutes optimal stream quality for long-form viewing, it found that 1.5Mbps to 2Mbps was more than su icient for viewing on an iPhone. “Your eyes can’t determine better perceptual quality beyond that,” says Munford. With live, event-based streaming, higher framerate is a positive, but it’s a must when it comes to eSports. “A 60p experience on mobile is arguably better than a 4K lower framerate experience,” says Carnahan. “The resolution does not necessarily make the experience more compelling, whereas higher framerates can.” Even BT Sport, which is investing in a future 5G network, understands that 4K UHD is not a good use of bits or bandwidth to mobile. “Going forward, our baseline for live events streamed to mobile will be HD 1080p, 60 frames a second,” says Matt Stagg, BT Sport’s director of mobile strategy. IS IT STILL AN HD FUTURE? Even content producers who are at the cutting edge of production are not yet swayed that the benefits of cost and convenience of working in HD have been overtaken by those of 4K. “The whole idea of resolution for a filmmaker is a bit of a myth,” says Robin Dimbleby, a natural history producer who has filmed lions and monkeys for Sky wildlife shows and who is currently filming in Indonesia for NHNZ. “The most important thing is for your story to come through properly. We don’t want to get into a resolution arms race which is why we do a lot of HD sequences still within our quota [of HD material acceptable for Sky’s UHD output]. “Who has a 4K TV? Everyone is still watching in HD.”
UPWARDLY MOBILE With increased use of mobile devices to watch live events, 4K has to work harder to convince users of its benefits
TECH SOLUTIONS The industry is creating some fantastic encoding e iciencies that make 4K VOD streaming viable by lowering the bitrate. Harmonic’s EyeQ Content Aware Encoding technology is claiming bandwidth savings for UHD HEVC up to 40%, for example. With VOD, the consumer doesn’t mind if it takes another 10-15 seconds to bu er up at the start of a program. But any lag with live becomes a real consumer bugbear. It’s considered pretty good just now to keep latency within the 10-12 second range for live OTT. Harmonic says its technology has already demonstrated end-to-end UHD HDR workflows with latency below six seconds.
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