The BBC isn’t alone in recognising 4K and HDR technologies are, in its words, “central to the future of high resolution TV”. And its aim to deliver the two technologies (as well as wide colour gamut) isn't unique. But what it can offer over rivals such as Sky, Netflix and Amazon Prime Video, is 4K HDR content for free - as long as you have a compatible TV, decent broadband connection and a TV license.
It’s been well over a year since the BBC made a four-minute snippet of Planet Earth II temporarily available in 4K on its iPlayer catch-up service. Just before Christmas it also featured the entire series of Blue Planet II, not only in 4K but also with Hybrid-Log Gamma (a broadcast-friendly version of HDR the BBC co-invented with Japanese broadcaster NHK).
Rumour soon spread the Beeb was gearing up for 4K HDR broadcasts of the 2018 World Cup this summer - especially after viewers spotted that a rugby match and the second half of the FA Cup Final appeared in 4K and HDR in April.
So what does this mean for the future of 4K and HDR, and how is the BBC getting involved?
A 4K trial, not a 4K service
No, it’s not quite time for couch potato 4K enthusiasts to stock the kitchen cupboards and buy new slippers. The BBC is still at the “trial” stage, so it’s unlikely we’ll get a deluge of 4K HDR content anytime soon.
Crossing every finger and toe won’t change the fact 4K BBC content is likely to trickle, rather than flood, through to iPlayer.
Why? Well, while not as complex as delivering a linear 4K broadcast channel (like, for example, the BT Sport Ultra HD channel), implementing 4K HDR content on to iPlayer still presents significant challenges.
As explained in a blog post written by the BBC R&D team’s technologist Andrew Cotton, and Phil Layton, head of broadcast & connected systems, the trial version of Blue Planet II was post-produced in HLG HDR, but it still needed HEVC encoding - with each episode taking about a day to encode.
With 11 different resolution versions having to be created to cater for varying internet bandwidths, it wasn’t quick work. But as Layton and Cotton write, “Our goal with these trials is always to leave the BBC with a better operational capability for the next trial. Each trial gets us closer to where we want to be…”
However, with the World Cup the Beeb’s third proper trial in eighteen months (following the 30-day access to Blue Planet II and the short Planet Earth II clip), it’s likely we’ll see the BBC ramp up its efforts to deliver big events - if all goes well during the broadcast of the summer's tournament, of course.
And that will be some milestone in advancing the broadcaster’s mission to reinvent itself for the next generation of TV.
The stream dream: live broadcasts
But, as Benjamin Franklin once said, “without continual growth and progress, such words as improvement, achievement and success have no meaning”. And the BBC knows it.
It may not have been the quickest process, but the trials have gone from mere minutes to hours and, more critically, from a catch-up workflow to a live equivalent.
Last year, Layton explained his “next challenge is live production workflows into iPlayer. We want to make this a routine operation”.
“A UHD channel… isn’t sustainable for what we have available right now. The OTT offerings offer a much more flexible route for delivering this content – and in a time-scale we couldn’t match for terrestrial.”
The duration and demand of the World Cup coverage – 29 4K HDR matches over the tournament weeks will no doubt attract thousands of 4K TV owners – has meant some conditions are attached to the coverage…
For example, World Cup streams will be available on a first-come, first-served basis. The Corporation has said “tens of thousands of people” will be able to access matches on the iPlayer home screen as soon as coverage starts, but when the stream is ‘full’ it will simply disappear from the page. So our advice to you is: get in there early.
Then there's bandwidth requirements. Viewers needed around 23Mpbs to stream Blue Planet II on-demand in 4K HDR and, while the World Cup trial uses the same distribution to iPlayer as Blue Planet II did (Main 10 Profile, Level 5.1 HEVC with HLG signaling), it has to use real-time encoding because it’s live - therefore, the BBC’s bandwidth requirements are higher.
A full 4K resolution (3840 x 2160) supposedly demands 36Mbps, while 20Mbps (around what was necessary for the on-demand trials) should get you a 2560 x 1440 resolution.
“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,” says Layton in his most recent blog post.
So what do you need?
Naturally, for both the World Cup and future 4K HDR iPlayer content, you'll need a compatible 4K TV or 4K set-top box running the correct version of the BBC iPlayer app to take advantage of both picture technologies.
A fair share of new and old 4K TVs from big manufacturers are compatible with BBC’s 4K iPlayer trials, although the list does change slightly on a trial-by-trial basis. For example, while Sky Q was compatible with the on-demand Blue Planet II content, it doesn’t appear to support the live World Cup broadcast.
In a nutshell, compatible TVs for the World Cup include Finlux, Toshiba, Panasonic and Loewe sets from 2015 onwards, select Sony models from 2016 onwards, and a number of 2017 and 2018 Samsung and Philips TVs. LG 2016 OLEDs and a wider range of models from 2017 and 2018 also support it.
A full list can be seen here.
Lucky owners of these TVs won’t have to update the iPlayer app. And as the first trial allowed the BBC teams to work with device manufacturers to solve the interoperability issues identified during its testing, compatible TVs should automatically switch to an appropriate HDR mode when the HLG signal is detected.
No HDR TV? No problem
The fact HLG signals are backward-compatible means those with non-HDR 4K TVs aren’t left out either, with these trials capable of delivering higher quality pictures to standard dynamic range 4K TVs that support the BT.2020 colour gamut.
As stated on a BBC blog post: “as the BBC iPlayer bitstreams use the HLG HDR format, viewers do not necessarily need an HDR TV to benefit from the higher UHD resolution and wider colour gamut of the UHD iPlayer bitstreams.”
In order to service as many people as possible, the BBC has purposely not locked it off to “HLG-supported” devices. Some TVs will deliver it in full 4K HLG, others will just be 4K.
And what about those with internet speed strain? The move from 8-bit AVC/H.264 compression (used for iPlayer’s HD streaming) to the 10-bit HEVC compression that supports HDR has made it possible to reduce the bitrate for a given resolution.
For example, while the highest HD quality currently delivered on iPlayer is 1280 x 720, 50 frames per second at around 5mbps, HEVC can supposedly increase that to 1600 x 900, and add both wide colour gamut and HDR, while demanding no greater bandwidth.
The argument that arose during the Blue Planet II trial centred around viewers' need for 23Mbps or so to stream in 4K HDR while a 4K TV could still stream “better resolution, wide colour gamut and HLG high dynamic range” even with a slower internet speed.
During the World Cup, 720 and 1080 resolutions are also available in HLG HDR, requiring a maximum of around 10Mbps.
No sign of surround sound
While immersive surround sound formats such as Dolby Atmos are being attached to 4K, HDR content, the BBC hasn’t yet secured 5.1 surround sound.
The audio for the World Cup will be stereo AAC-LC at 128 kbit/s.
“Whilst we would like to provide multi-channel sound, we have found a number of issues with receivers which are difficult to work around. We will continue to explore solutions for future events,” says Layton.
Fingers crossed for surround sound in the future, then, but for now we’ll have to settle for good ol’ stereo.
So, how does it look?
We had (ahem) a whale of a time watching the Blue Planet II iPlayer trial, and were suitably impressed by the explicitness of the delivery from the finely etched details to the vibrant colours of the coral. We thought HDR made the standout difference, and all-in-all the trial provided a markedly improved experience over the HD SDR version also accessible on iPlayer at the time.
Of course, we're more than a handful of matches into the World Cup and, as far as picture quality is concerned, it's a absolute blinder... when it works. So far the iPlayer streams have got mixed reviews, proving a little flakey at times - we imagine when there's been heaviest demand. There's been some out-of-sync sound issues and reports of buffering, but largely the trial can, so far, be heralded a success. The BBC must think so too as it has already announced an extension to the trial that will see 2018 Wimbledon tennis matches broadcast live in 4K on the platform next month... ace!