Seven years on from its inception, one has to question whether the Ultra HD Forum is still relevant at an IBC Show where hardly anyone was talking explicitly about UHD, but where several were demonstrating live 8K with VVC encoding.
Nevertheless, as an industry group tasked not with producing standards but on nurturing users of them through navigable UHD guidelines, the Ultra HD Forum will feel that its mission is far from complete.
Besides, what keeps the Forum plugging away (or awake at night) is the knowledge that people are still not using UHD standards correctly.
The handling of chipsets is one example, with poorly executed auto HDR conversions being baked into TV hardware. In some instances, but not all, consumers can sift through menus and eventually figure out how to turn off auto HDR. But in reality, is anyone going to bother?
This ties into sustainability debates, another key theme of IBC 2022. Faultline heard some unsubstantiated figures floated about huge spikes in Watts consumed during SDR to HDR conversion on set tops, even for TV sets or content without HDR compatibility. End users are guzzling power pointlessly without even knowing it, no thanks to afterthoughts in engineering processes.
Will content providers like Netflix, which are full-steam ahead with HDR, attempt to rectify these afterthoughts by encouraging subscribers to be greener streaming citizens by down-converting to SDR? Not a hope in hell.
Netflix wants to ensure the best possible viewing quality and most immersive experience. Netflix can afford to push auto HDR because a sizable portion of its content library is available in HDR.
While there is no specific reference to auto HDR conversion in the Ultra HD Forum’s latest guidelines, version 2.6 released in Spring 2022, it does provide an update to the section on Color Accuracy including new plots showing the effects of incorrect look up tables when converting between HDR (Rec 2020) images and SDR (Rec 709) images as well as the conversions between PQ10 and HLG10 video images.
We suggest common members of both the Ultra HD Forum and Greening of Streaming should start a working group on these issues. Unfortunately, after browsing the respective member lists, it seems that sole responsibility falls to French encoding expert Ateme as the only mutual member (although Synamedia recently acquired GoS member Quortex, and we understand is in the process of upgrading its membership).
It’s important to note that SDR to HDR conversion can occur at different points in the workflow between production and CPE. The latest Ultra HD Forum guidelines advise that real-time program service providers should not expect CPE to render seamless transitions between segments of content that have different transfer function or system colorimetry.
There are two techniques for SDR to HDR conversion, as defined by ITU-R BT.2446-0, with particular advantages and disadvantages.
To paraphrase the latest guidelines, remapping is preferable if a service provider intends to simulcast a UHD service in SDR for backward compatibility. This is because content that was originally SDR will remain exactly as intended in the legacy version of the service.
On the other hand, a service provider may want all segments to appear uniform to ensure a consistent consumer experience, where up-mapping would be more appropriate than remapping.
The Forum also warns that, under some circumstances such as viewing in a darkened room, HDR displays and content can cause discomfort if consideration is not given to the viewer’s vision adapting to the average light level on the screen at any given moment.
If a feature program has a low average light level such as a night scene (Game of Thrones: Series 8, Episode 3 – we’re looking at you) and the picture is abruptly cut to a high average luminance scene, the viewer may experience discomfort as their eyes adapt to the change in lighting level.
Particular consideration should be given to placing ads with respect to transitions from dark to light, advises the Forum.
There are still goals to be met until the next set of guidelines are released, namely to convert all source formats to a single, internal format within each environment – HLG for Production, PQ for Transmission. Another goal is that production shall feed both the native HDR formats and the legacy SDR formats with the eventual goal of switching transmission to accepting a single-stream deliverable.
This is not just an issue of production choices, content providers, or TV manufacturers, as some operators make decisions to do auto HDR conversion too. This of course is where difficulties arise, as network operators are not typically TV people. Technical reasons are not always the best reasons to upconvert.
There were six demos on total gracing The Ultra HD Forum stand at IBC, mainly replicating for European visitors what it was showcasing back at NAB:
- HDR Down-mapping and Matching supported by BBC, B<>COM, Comcast NBCUniversal, and LGE. Content showing various HDR/SDR conversions.
- HDR Color Management supported by LGE. Interoperability challenges for displaying HDR-based content.
- SDR Rendering Compensation supported by BBC, Comcast NBCUniversal, and LGE. Shows results of applying the BBC and NBCU compensation LUTs to match different peak brightness of displays.
- Live Audio Production using Serialized ADM supported by Ateme and Dolby. End-to-end use of S-ADM for producing live audio components over IP.
- Live and Low Latency Streaming with VVC supported by Ateme, KPN, LGE, and MediaTek. Live encoding undertaken off-site is made available via DASH over fiber to local router/end devices.
- Multiscreen OTT with CAE and Low Latency supported by Brightcove, Dolby, Harmonic, and KPN. Ultra HD OTT interoperability on multiple device types, featuring HDR10 and Dolby Vision.