Inside the BBC 4K UHD Hybrid Log-Gamma (HLG) iPlayer trial: The DTG and BBC speak out

The BBC’s first UHD 4K content trial on iPlayer has been hailed as “significant” by David Daniels, Project Director AV at the DTG (Digital Television Group). He told Inside CI that it’s “highly likely to be followed by full time services.”

The trial has seen UHD footage from the Planet Earth 2 show delivered via iPlayer for the first time, on select Panasonic 4K TVs, as well as VirginMedia’s V6 set top box and most recently the Sky Q 2TB STB. The BBC has been tailoring the trial to fit different receiving technologies. The trial will be available until early next year.

The move points to UHD content breaking away from pay TV environments for the first time, and cements Hybrid Log-Gamma (HLG) as the technology of choice for broadcasters looking to implement HDR (HighDynamicRange) video.

Hybrid Log-Gamma is a joint development between the BBC and NHK.

“The BBC has been privately testing UHD for some time, and this isn’t the first public trial - it provided last year’s Queens Speech in UHD. However, this is its first HDR/HLG trial so it is significant for the addition of High Dynamic Range, meaning the promise of delivery of so called “better pixels” can be tested in a real world environment,” Daniels exclusively told Inside CI.

He says that the trial will help both the BBC and the DTG see how distribution and production workflows work and help promote an open approach to HDR UHD that will doubtless be of benefit on a wider perhaps even global basis. 

“In addition, by trialing UHD in this way on iPlayer, we will be able to assess how many devices are capable of receiving such services and perhaps as importantly how well the infrastructure is capable of delivering these in an OTT environment.”

According to Daniels (pictured), the HDR HLG trial will “highlight any issues with backwards compatibility both in the displays that are currently in production, but also in the infrastructure available to deliver such services. There may well be unforeseen challenges in streaming such bandwidth hungry programming and any trial can only help us to find ways to overcome them.”

Currently there are no consumer displays able to present HDR HLG. Panasonic confirmed to Inside CI that it had no plans to action an HLG firmware update on its 2016 4K sets. However all the major screen manufacturers are expected to introduce HLG enabled 4K televisions in 2017. Viewers on non HLG sets will see an SDR 2160p image.

According to the DTG, the iPlayer clip has been graded for HLG and that the signalling is compliant with current DVB standards for UHD. “Given the latest release of TS 101 154 (the DVB standards for AV) includes their guidelines for HDR using both PQ and HLG, the hope is that this trial will encourage manufacturers to fully implement that standards in their next production displays,” notes Daniels.  “Indeed, the joint DTG and German TV Platform Plugfest earlier this month saw some early implementations of the technology.”

Andy Quested, Head of Technology BBC HD and UHD SMPTE fellow (pictured above), speaking exclusively to Inside CI, confirmed that the trial was graded on an HLG display. Explaining the thinking behind the move, he told me “What it does prove is the compatibility with non HDR displays as you suggest. The grade used an HLG display - great thing about HLG is no need for an ‘HLG workflow’. It's just the same as SDR other than the display used in the grade and any subsequent graphics finishing.”

So will 2017 be the year that HDR becomes a broadcast reality? Daniels is optimistic.

“The joint DTG and German TV Platform Plugfest demonstrated that the technology is available, and trials of this sort can only encourage manufacturers to roll this out in their new products, and this is highly likely to be followed by full time services to become available to satisfy the inevitable demand for HDR phase 2.”

One key question as yet unresolved about HLG remains unanswered. Will Hybrid Log-Gamm really come to market as HLG, perhaps the most inscrutable of all tech acronyms, or will it get a consumer friendly rebrand

“This is really a marketing question,” admits Daniels.  “It has to be hoped that whatever it is sold as, there is a good level of education for both retailers and consumers as to what is actually being presented. “

The DTG hosts uhdready.co.uk to help consumers match services with displays, to aid in that education.