Brightness range extends with HDR.
New technology formats, High Dynamic Range (HDR) and Wide Color Gamut (WCG) along with 4K and UHD provide stunning improvements in imagery. But, with such a dynamically changing format landscape, will the purchase of infrastructure to support these improvements ever pay off? Outsourcing the required coding tasks to a service may be a better solution.
While 4K may have gotten off to a slow start with many in the entertainment and distribution industries approaching the format with the same skepticism as 3D, the momentum cannot be denied. By some estimates, 4K adoption, as measured by household penetration (HH) of 4K Ultra High Definition (UHD) television sets, is trending ahead of initial projections and likely to reach 35% by 2019. This is years ahead of the adoption curve that the industry witnessed for HD.
If the adage holds true that “Content is King,” how can the 4K market be developing so quickly given that content availability is limited? We know this is the case because of the small number of new releases in the UHD format and few titles in the content libraries offered by highly publicized 4K consumer services. Fast adoption can be traced in large part to declining television prices, television purchase refresh rates, and the way that 4K sets stand out against their HD competition on the showroom floor. The reason for their eye-caching appeal is the dramatic color difference UHD offers.
With the introduction of Rec. 2020 both on chipsets and within next-generation displays, the appeal of 4K, when compared to HD, is evident to any layperson. With a coding scheme of 10- or 12- bits per color, Rec. 2020 generates approximately 1.07 billion colors with 10-bit coding and a whopping 68.7 billion colors with 12-bit coding. By comparison, ITU-R’s Recommendation BT.709 or Rec.709, the foundation color depth standard for digital TV since 1992 and High Definition (HD), prescribes a bitrate of 8-bits per color with 256 gradations per primary color, for a total of approximately 16.8 million possible colors.
Ender’s Game, courtesy of Lionsgate
High Dynamic Range and Wide Color Gamut
Now, enter High Dynamic Range (HDR) and Wide Color Gamut (WCG). The picture quality enhancements are stunning; the goal of HDR being to more closely match the dynamic range of the human visual experience in the natural world.
What the various HDR modes vying for market acceptance all have in common are (a) support for a much wider color gamut, (b) greater contrast dynamics with deeper levels of black in the darker pictorial elements and (c) far greater luminance in the brightest white and color elements. WCG will increase color accuracy, particularly in shades of green, blue-green, yellow-green and reds.
The human eye can detect a luminance range from one millionth (0.000001) of a nit (the metric used to measure display brightness) to about 100 million nits. For formulating HDR displays, the goal, of course, isn’t to match this range, but rather, to operate within a dynamic contrast range that is closer to what the eye experiences in the natural world as a person’s gaze moves from bright to dark backgrounds. In other words, the instantaneous dynamic range available to human perception as a function of pupil dilation and other opto-physiological processes in real-world situations. So, for example, an LCD HDTV puts out 300-500 nits while the new HDR-displays crank out more than 1000 nits.
The broadcast and production challenge
While the science and math are well understood, what’s indisputable is that the picture difference HDR provides is dramatic and can be readily observed on the television screen, providing a far more engaging and visually compelling experience. Consumers will forever demand the best quality viewing experience and HDR fits the bill. So, while TV manufacturers may have been the early catalyst, Hollywood, broadcasters, and service providers are taking note and embracing this next generation viewing experience to differentiate their service and capture consumers and subscribers. Easier said than done.
From a Video on Demand (VOD) perspective, bringing HDR to the home is challenging for several reasons:
- Massive files and source materials: The key to achieving high quality Standard Dynamic Range (SDR) and HDR HEVC outputs is using high bitrate source material. For episodic content, we often see a need for > 600 Mbps source. For difficult-to-compress high action, such as CGI theatrical materials, using >1 Gbps v210 masters is necessary to achieve stunning contrast, luminance, and color gamut. The typical service provider’s back-office systems and workflows are not designed to handle these bitrates.
- Competing formats and lack of standards: Studios and broadcasters have not universally adopted support for all formats and standards continue to evolve. Recent format technologies such as DVD, Blu-ray, 1080i STBs and 1080p TVs took 5 plus years to develop in hardware. By contrast, 4K SDR and HDR developments are trending like software and internet technology cycles that evolve and change very quickly. These shortened cycles are possible due to the advent of the powerful, inexpensive audio / video System on a Chip (SoC) and its ability to be adapted to support new media formats with relatively low cost, quick software changes. As such, content availability across all platforms/devices is constrained.
- Packaging variants: MPEG-DASH, the Adaptive Bit Rate (ABR) manifest of choice for 4K and HDR, has two playback modes called Live and VOD. Early implementations of MPEG-DASH do not support both VOD and Live playback modes. Further, some early 4K UHD TV implementations from CE makers are not MPEG-DASH compliant. These first-generation devices require special QC testing.
- Bandwidth: Balancing bandwidth and quality will remain an issue even with the next generation HEVC codecs. Whether delivered over an IP network or OTT, HDR requires more bandwidth. When comparing HEVC/H.265 versus AVC/H.264 at the same bit depth, HEVC is ~50% more efficient; meaning one can use 50% less bitrate if the same content is encoded as HEVC. However, this is somewhat overstated as it is based on a reference HEVC encoder, which would not be part of a production workflow since the encoding speed is not optimized. Today, HEVC will likely result in 30% better encoding performance, which will improve over time. If 10-bit HDR HEVC is compared against 8-bit SDR HEVC, the HDR 10-bit stream will roughly require 10% more bits to be at the same quality level. But, the industry is already looking forward with 12-bit color streams, which will raise additional issues for today’s delivery networks.
With all these challenges, how do we bring HDR VOD to the home?
Let someone else do it for you
On the delivery side, current industry thinking is that the HDR experience mandates 3840 X 2160p @18-20 Mbps. However, at Deluxe, we’ve been working with distributors to demonstrate that they can go to market with 4K service “tiers” and optimize ABRs to fit within network constraints.
Working with both theatrical and episodic content at the traditional HD resolution of 1920 X 1080p, HDR VOD looks great when scaled up by today’s 4K HDR-enabled TVs. At 4-5 Mbps, this 1080p HDR content is well within acceptable bandwidth thresholds of most networks. Upper 4K bitrates are “hidden” until ready for utilization by the distributor. Assets can be delivered HDR-ready with the required ABR layers ranging from 720p to 1080p, 1440p and 2160p (NOTE: Deluxe uses 3840 masters when creating 720, 1080, 1440 and 2160 ABR layers). Initially, the higher bitrate 2160p layer is not referenced in the asset manifest but can be turned on later, when required, with a simple update to the manifest. Pre-delivery of 2160p to the Origin does not load the CDN until the network is ready and is an intelligent way to implement backward compatibility of SDR and HDR.
With this approach, distributors can provide tiers of service that support the migration of 4K SDR to HDR that starts with 1080p HDR; and with manifest manipulation, enables them to upgrade to 2160p HDR when they are ready.
As with any technology shift, broadcasters and service providers are faced with choices: (a) invest internally in nascent technologies that are likely to be obsolete once the market matures, (b) outsource workflow requirements and capabilities that negates the massive investments and risks, or (c) some combination. A managed service can bridge the gap today by offering services such as HD with HDR and SDR to HDR conversion and also future proofs for tomorrow (delivering UHD variants now and updating manifests only when ready). Given the shortened technology cycle, dynamically changing landscape, and sheer complexity of 4K and HDR, an outsourced managed service approach makes even more sense to minimize deployment time-to-market and costs of delivering HDR in an IP world.
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