Netflix has started streaming content in Ultra HD (UHD), branded as Ultra HD 4K. UHD is approximately 4 times the resolution of Full HD. Netflix is streaming UHD content as its highest bandwidth profile at 15.6 Mbps, referenced on Netflix’s in-app player as 2160 HD. UHD streaming has currently only been rolled out for House of Cards season two. The video stream is compressed using next generation h.265/HEVC, therefore requiring both an HEVC decoder, as well as an updated version of Netflix’s client player. Netflix UHD clients are already embedded on UHD TVs offered by LG, Samsung, Sony and Vizio.
Netflix’s move from content platform to content producer with the commissioning of original series such as House of Cards has opened up a lot of unique options for Netflix. Being able to make content in UHD means Netflix has a rarefied content library where otherwise UHD content is scarce.
However, UHD is still in its very earliest days. The standardisation of 3840x2160 pixel UHD-1 (versus 1920x1080 Full HD) was only agreed in August 2012. In the last year TVs and decoders have had to catch up to make viewing UHD TV possible. Much like HD, UHD has a sister variant for video production and cinema distribution that is slightly larger – called 4K (4096x2160) and 2K (2048x1080). This has often resulted in mixed branding and consumer messages around UHD, which has not yet been standardised as a consumer label by industry organisations. The result is that some marketing uses the term 4K (mostly incorrectly), Ultra HD or UHD. All terms are typically referencing UHD video signals.
With four times as many pixels, Netflix’s UHD video needs four times as much space to transmit the same video stream. What is typically shown for broadcast TV is 1080i50/60, Full HD video at 50 or 60 interlaced (half) frames per second. UHD is going to start with 2160p25/30, which means UHD resolution with 25 or 30 full frames (progressive scan). The resulting image is therefore just 4 times as much video, with a slightly different frame cadence. Netflix’s top tier HD stream is 5.8 Mbps at 1080p30, while UHD will be streamed at 15.6 Mbps. In order to achieve higher quality when the required bandwidth is otherwise four times higher, Netflix have utilised HEVC, which is approximately twice as efficient as the h.264/MPEG-4 used for its HD stream.
But there is more in the discussion about UHD than just resolution increases. With the higher pixel density problems like motion blur become more evident without increasing the frame rates (50 or 60 frames per second are likely). There is also a strong motivation from the industry to use this opportunity to increase the colour information from 8-bits used in HD to 10-bits for UHD. All things equal, increasing the frame rate from 30 to 60 frames would double the amount of bandwidth needed, while increasing the colour depth from 8-bits to 10-bits would increase it by another 25 per cent. Added together an average Full HD stream might multiply from 6 Mbps to 60 Mbps before using HEVC, which would bring the bandwidth back down to around 30 Mbps. Take out the extra frames and colour, and you’re approximately doubling the bandwidth (4 times the information, but twice as efficient). This is closest to what Netflix are offering.
Below about 11.7 Mbps, Netflix adaptive bitrate algorithms will downscale the UHD signal to an HD signal, so a consistent stream of about 12 Mbps to the home is needed (Netflix recommend 15 Mbps). Where does this leave consumers? Currently only around 15-20% of homes in the UK would qualify, and significantly less in many other markets. Layered on top of that, homes would have to be both Netflix subscribers and have a UHD TV with an updated Netflix client embedded. With UHD shipments making up less than 3.5 per cent of shipments in 2014 for North America and Western Europe, it’s likely that this particular service and technology will be reserved for only a small number of homes for the foreseeable future.