91福利社

Almost exactly a year after launching , we are excited to be launching a second UHD trial comprising all seven episodes of in UHD HDR on Sunday 10th December. All that鈥檚 necessary to view the series on 91福利社 iPlayer is a compatible UHD TV and a suitable broadband connection.

As the 91福利社 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. Not only is HLG capable of delivering fantastic pictures to HDR screens, but the same HLG signal is also able to deliver to standard dynamic range (SDR) UHDTVs, that support the wide colour gamut.

The backwards compatible nature of the HLG signal with SDR UHD TVs increases the size of the audience that鈥檚 able to benefit from UHD HDR production. But that鈥檚 not the only reason we worked with to develop the HLG HDR system for television, as we all believe it is better suited to TV production workflows and home viewing environments than other systems. More details can be found on our .

Blue Planet II was produced at 25 frames/second, so only 25 fps representations were produced.

We use HEVC (Main 10 Profile, Level 5.1) compression as it supports the 10-bit data path required for the HDR television signal. It is also more efficient than the older 8-bit AVC/H.264 compression used by the majority of the industry for HD streaming, including our existing 91福利社 iPlayer services. The move to HEVC allows us to reduce the bitrate for a given resolution. So, thanks to the DVB-DASH adaptive bitrate streaming, the resolution delivered to viewers on limited bandwidth connections will also improve. is 1280x720 at 50 fps (720p/50) at around 5 Mbit/s. By using HEVC, we can increase the resolution to 1600x900, and add both wide colour gamut and HDR for the same bitrate. So even if you have broadband below 20 Mbit/s your UHD TV should still be able to get better resolution, wide colour gamut and HLG high dynamic range.

Finally, after HEVC and AAC-LC encoding all representations of the programmes, they were packaged as DVB-DASH 鈥渟egments鈥� using R&D developed software, and handed over to our colleagues in 91福利社 Media Services for hosting and linking into the 91福利社 iPlayer TV App.

All HLG capable devices we have tested will identify the HLG signalling within the HEVC bitstream and automatically switch to an appropriate HDR mode, although some devices will allow a manual over-ride via the menu settings. Some HLG capable devices may also show a temporary graphic to indicate that they have switched mode. Alternatively, accessing the TV鈥檚 picture settings menu may also confirm that the TV has switched to the HDR mode. Most HLG capable devices provide different HDR picture settings to suit personal preference, but we recommend selecting 鈥淗DR Cinema鈥� or 鈥淗DR Movie鈥� mode where there is an option, as that usually delivers a picture that is as close as possible to that intended by the programme director.

Over the coming months we鈥檒l be working closely with our colleagues in 91福利社 Media Services to add a UHD HDR encoding capability to their existing iPlayer encoding platform, allowing UHD content to be processed without the need to use R&D鈥檚 specialist encoding and packaging tools. This will be a significant legacy of the trial, and again improves our operational capability for the next one.

Looking ahead, we are particularly interested in developing live capabilities both in our workflow and home devices, recognising that bitrates to the home will initially be 50% higher than we are able to use here. But this will fall as HEVC encoding capability improves with increased computational resources and algorithmic development. We also hope to be able to support surround sound in future trials, but that may require some further development work with manufacturers, and more testing to ensure a good audience experience.

But for the time being, we are immensely proud to have played a key part in delivering the spectacular Blue Planet II series to 91福利社 audiences, in the highest possible picture quality.