Streaming Media
Live UHD streams of World Cup football over iPlayer are a BBC first, but HDR is not under the corporation's full control.
The BBC's planned UHD HDR streaming of the FIFA World Cup Russia to viewers in the U.K. will be another milestone on its path to producing and delivering all its programming over IP. It seems to have chosen BBC iPlayer as the main pathway to delivery of UHD content, and in recent weeks has upped its research and development into making this happen.
While a significant leap forward in terms of quality (this is the first time that BBC iPlayer has offered such a high-quality stream) and scale (29 matches will be streamed live), its World Cup workflow will not be the finished article. The BBC has been quite open about this, referring to its World Cup streams as a trial. It plans to only reach tens of thousands of viewers with the full UHD HDR stream because of bandwidth issues.
One other hiccup is that the workflow for high dynamic range (HDR) video from Russia is not how the BBC would ideally like to move forward.
The BBC will base its coverage on the FIFA UHD HDR host feed and add its own studio presentation up-sampled from HD.
The iPlayer stream will use the Main 10 profile, and level 5.1 HEVC with HLG (hybrid log gamma) signalling. This is the same encode used for the BBC’s Blue Planet II trials (available on-demand in UHD HDR), for which the corporation was able to use non real-time encoding. For the live soccer coverage, however, real-time encoding is required and so the BBC will be offering the following four encodes: 3840 x 2160p50 at 36Mbit/s, 2560 x 1440p50 at 16Mbit/s, 1920 x 1080p50 at 10Mbit/s, and 1280 x 720p50 at 7Mbit/s.
Since a minimum capacity of 40Mbit/s is needed to get the full 3840 pixel resolution running at 50 frames per second, this restricts the number of viewers able to receive the World Cup streams.
“A 20Mbit/s connection should be capable of providing the 2560 pixel resolution representation,” says Phil Layton, head of broadcast and connected systems for BBC R&D. “As HEVC encoding develops we very much hope the real-time encoders will be capable of matching and eventually bettering the bitrates we use for on-demand, but this will require a big increase in computational power.”
Streams will be packaged with DVB-DASH using BBC R&D-developed software with final distribution via CDN.
“The adoption of open international standards means that iPlayer gains the capability to decode UHD HLG using the capabilities of the receiver it is running on,” Layton says.
The BBC has played a major role in developing the HLG production format for high dynamic range, and HLG remains its preferred option. However, for the World Cup it has to take the host feed which is likely uses the Dolby PQ standard.
The BBC will convert the host feed to HLG for iPlayer so that standard dynamic range UHD receivers will be able to exploit the backwards compatibility of HLG.
This universality of service is core to the public service broadcaster's mandate. It’s why it devoted so much time and effort developing HLG in the first place.
The BBC has continued that process by developing and testing a means of ensuring that SDR (standard dynamic range) content derived from an HDR workflow is consistent in terms of colour and light values for onward distribution. This "scene-light format conversion" underwent a large-scale test at the Royal Wedding last month.
While the Royal Wedding wasn’t transmitted in UHD, it was captured in UHD HDR (HLG) for posterity.
“Simple scene-light format conversion might at first seem like a small step towards completing the HDR production eco-system,” explains BBC R&D principal technologist Andrew Cotton. “In fact, the problem of ensuring near identical colours in SDR content derived from an HDR workflow, compared with those from an SDR production workflow, is one that the whole industry has been trying to solve. It has so far proved a block towards the widespread adoption HDR live production.”
According to Cotton, this type of conversion has proved particularly difficult to achieve because the majority of HDR down-converters on the market, including the BBC’s own licensed down-conversions, are based on "display-light" conversion technology.
“That means the conversions calculate the light emitted by a reference monitor being fed the input signal, and then convert that signal to one that would cause exactly the same light to be emitted by a reference monitor operating in the desired output signal format,” he says.
The BBC used scene-light format conversions for live coverage of the Royal Wedding. In this case the HLG HDR signal was converted to SDR (BT.709) after the UHD production switcher.
Further details on this process can be found on the BBC blog.
“For future events we hope the ground-breaking work at the Royal Wedding will lead to simpler, native HLG workflows which allow HD, UHD, and UHD HLG versions of the event to be produced from the same camera feeds and without the complexity of metadata to manage through the broadcast chain,” Layton says.
Although FIFA is offering 16 channel object-based audio (based on Dolby’s system) the BBC explains that multi-channel sound, while desirable, was not possible for its coverage on this occasion. This is due to a number of issues with receivers which “are difficult to work-around.” Instead, its audio will be stereo AAC-LC at 128 kbit/s.
UHD Match Coverage
In terms of FIFA’s host production, the BBC will field 37 cameras at each of the 12 stadia in Russia with 37 cameras (up from 34 in Brazil 2014) including 8 UHD/HDR cameras capable of simultaneous 1080p/SDR output and another 11 cameras with 1080p/HDR and 1080p/SDR dual output.
This basic match-day coverage is supplemented by eight super slow-mos, a cable cam, and a Cineflex Helicam. Two ultra-motion polecams join the roster from the quarter final stages.
In addition, it will use two radio frequency cams at each venue to record fans inside and outside the ground.
Around 75 percent of the live match cut is estimated by FIFA to be in full UHD HDR with the remainder up-converted. All replays, for example, will be up-converted from HD “with minimal visual impact on the UHD feed due to the natural softness derived from the slow motion angle,” advises FIFA.
Social Media From Russia
FIFA has a dedicated social media production team—another first—tailoring content for Facebook, Twitter, Snapchat, and Instagram in order “to boost engagement and spark online interaction.”
Its shareable content is designed to stand out on busy news feeds and offer short-form video with “simple, enlarged text and thumbnails” that give the user an imperative to press play.
Since most broadcasters already run their own digital platforms, FIFA is making SDKs available, composed of widgets, which deliver key data and editorial components. The aim is to help broadcasters integrate social media content into their existing digital platforms.
The white label web solution includes the matchcast alongside multi-angle content, VOD clips of events between matches, stats, and social media integration.
VR First
For the first time at a World Cup, VR (virtual reality) video will be available for all matches as a live stream in 180°, as well as 360° VOD to rights holders.
The 360° VOD clips will be made available for Samsung Gear VR, PlayStation VR, Google Cardboard and Daydream, and Oculus Rift players. Clips will also be published to Facebook 360 and YouTube VR.
FIFA commissioned a white label app from Deltatre (branded "FIFA World Cup VR") for the event, and requested customizations. The BBC is one of the rights holders taking this.
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