The ultimate goal of the Ultra HD Forum is to make all components of the delivery infrastructure as readily interoperable as possible, both to enable operators to go with their chosen vendor for each part, but also just to ensure that it all works properly and delivers the promised gain in quality of experience to consumers. While the Ultra HD alliance is charged with dealing with the devices at each end of the chain, such as cameras and TVs, the Forum’s remit is everything in between, so that its evolving guidelines embrace the full end-to-end workflow for constructing a real-time linear service. This must enable both live and recorded content to be delivered “glass to glass” from production to the consumer.
The guidelines therefore have to address every step in the chain in turn, as well as all the technologies involved along the way. The latter include compression, metadata carriage options, sample bitrate for ABR (Adaptive Bit Rate) services, audio, captions and subtitles, as well as all the options specific to UHDTV. These options latter come under four separate pillars, HDR (High Dynamic Range)/ WCG (Wide Color Gamut), HFR (High Frame Rate), high resolution (4K at 3840 x 2160 as well possibly as 8K at 7680 x 4320 later) and next generation object-based audio. The guidelines have to cater for content being manipulated at each point in the chain, for example by ad insertion or overlaying of graphics.
As if this is not enough, the Forum has to aim at a moving target, complicated by the fact that it is not itself the originator of the relevant standards, which instead come from bodies like MPEG, DVB, ATSC and ITU. The main area of concern has been HDR, as was noted by Ian Nock, Founder and Managing Director of London based TV consultancy company Fairmile West and leading participant in the Forum’s Interop Working Group (WG). “Everyone knows UHD itself is pretty much done, with a working HEVC solution, but HDR is still quite troublesome because there are many ways to achieve the same results,” said Nock.
For this reason HDR is a major focus at this year’s IBC in Amsterdam, which we discuss in a separate blog. The challenge here is that HDR emerged quite late in the day as a major part of the UHD technology set after it became clear from focus groups for example that it gave the biggest wow factor of the four UHDTV pillars. At the same time there are several variants as well as a consensus that they are all to an extent still work in progress. “People are trying to develop better ways forward, because ultimately these implementations today are stepping stones to even better ones in future,” said Nock.
In fact the eventual objective is to condense down to just one HDR profile that incorporates the best of existing ones, especially the two currently specified in the Forum’s phase A guidelines, the open HDR10 standard and HLG (Hybrid Log-Gamma) developed by NHK of Japan and the UK’s BBC. “If you’ve got three implementations of HDR and existing HD as well, you don’t want to broadcast it three or four times but just once,” said Nock. “So you want one video service that works on every device, regardless of whether it supports SDR (Standard Dynamic Range) or any particular flavor of HDR.”
This leads on to another challenge for the industry, which is backwards compatibility with existing TV sets. The TV industry collectively faces a public credibility problem here since CE makers came out with TVs billed as UHD capable but which only implemented 4K resolutions, along with more advanced color mapping in later models. Naturally emerging services including HDR should not only work with these TVs but deliver as much of the higher quality experience as possible. “This is quite a challenge,” Nock agreed. Many early 4K TVs are not HDR enabled, and this will be continue to be a challenge for a number of years.”
Again backwards compatibility is something of a moving target because it can be provided in several ways depending on the type of service and the specific parameters of the content, even if it conforms with the Forum’s Phase A guidelines. As one example, HLG10 is designed to provide some degree of backward compatibility with an SDR TV set that supports the colorimetry of the delivered signal, in BT.2020. But when using HDR10, inherent backward compatibility is not expected, so that a step down conversion must be done at some point in the distribution chain. To cater for such variations several alternative methods of serving legacy consumer devices are included in the Forum’s guidelines (BT.2020 is the ITU recommendation defining various aspects of UHDTV, most notably the bit depth and color space, which have been expanded to yield more realistic pictures).
While the continuing state of flux around UHDTV or more especially HDR means a lot of work for the vendors involved and the Forum itself, there will be one notable beneficiary from the complexity according to Nock, the set top makers. “I see this as an opportunity for set top boxes, because they offer a way of harmonizing services to the end consumer by offering processing capabilities to adapt content to the TV’s capabilities.”
Nock noted that people still tend to change their TVs within a five to 10 year cycle while set tops have a much shorter life of two to three years and even this is coming down with the reduction in size and cost of units, including attachable HDMI dongles. Such devices will provide the capability to deliver as universal a service as possible to the consumer during this period of technology flux. Operators will be able to transmit a HDR service as a single version and then rely on the set top box for the adaptation to display on SDR TVs as well as the latest HDR models. So UHDTV will ensure that the long predicted death of the set top is postponed even further.
Meanwhile the Forum’s Interop WG will play a key role specifying and testing the different combinations within the ecosystem that lie behind the set top box, which of course is an essential first step.
Join the UHD Forum Masterclass at IBC 2016 as they host a free-to-attend session covering this topic and much more on Monday 12th September. Full session details and speakers