Latest thinking on UHD bit rates and upscaling

While online video providers will be able to pioneer 4K viewing for the public using bit rates as low as 10Mbps (for movies over broadband), the introduction of true Ultra High Definition (UHD) television on broadcast networks will start at around 15Mbps, while we could see bit rates as high as 30Mbps initially, using the best current available HEVC/H.265 compression.

Although consumer marketing is confusing the two, there is a big difference between 4K television, which delivers four times the pixels of HDTV, and what is being talked about as true UHD, which quadruples the pixel count but also supports at least 50/60 frames per second and at least 10 bit colour depth.

Ian Trow, Senior Director Emerging Technology & Strategy at Harmonic, a leading encoding and storage vendor, says 10Mbps would yield a good quality 4K experience for cinematic content today running at 24fps (frames per second). “That is why it is no surprise that Netflix currently offers an HEVC service at 11 Mbps, with the option of a higher quality 15Mbps offering,” he says.

“For higher frame rate material typical on a linear television, 15 Mbps is required to deliver an improvement over HD at 50/60p [frame rates]. For premium performance, such as high-profile sports events, 20Mbps would be reasonable if  50/60p is the frame rate. If 100/120p [frame rate] is adopted, you would need closer to 25Mbps to cater for the extra temporal fidelity. This is for full resolution Ultra HD.”

Keith Wymbs, Chief Marketing Officer at Elemental Technologies, another company leading the charge for HEVC-based encoding of 4K/UHD, reckons that at the high end of the range, we could see some Pay TV operators dedicating as much as 30Mbps for live UHD sports content. “At the low end, we can see IP-streamed UHD movies in the low teens [bit rate],” he comments. Wymbs expects satellite operators to push the boundaries to impress early-adopters.

Trow points out that it is perfectly feasible for lower resolutions to be adopted at lower frame rates to experiment with the new format, particularly while the commercial case for linear broadcast Ultra HD is being made.

It is not impossible that H.264/MPEG-4 AVC could have a role in the early days of UHD, either, on certain networks at least. Peter Fregelius, Head of Entertainment Devices at Swisscom, whose company is considering a UHD VOD launch for 2015 (with no firm decisions made) says the most realistic compression option is HEVC. But he adds: “It is not a must for an operator. We could also offer it with H.264 over fiber access.”
 
The roll-out of UHD could have an impact on HDTV. To start with, upscaling will play a part in the early UHD services while channel owners fill their schedules with true Ultra HD programming. Trow thinks most early content forming an Ultra HD service will be HD, in fact, and this could persuade operators to throw more bandwidth at these HDTV channels.

“Even assuming good quality up-conversion, the encoding bit rate for HD must be larger to deliver a respectable picture,” he argues. “What this means is that an existing HD H.264 signal will look poor on an Ultra HD screen if it is directly applied. From our experience, I would say an extra 2Mbps is required to deliver a good quality result, so 8Mbps in total.”

Technology improvements like DVB-S2X, the new satellite modulation standard, and HEVC will benefit HDTV. At International CES 2014 in January, Broadcom announced two new SoC devices for entry-level satellite set-top boxes, which are now sampling, that support HEVC decoding. These are not aimed at the UHD market, but at helping operators to deliver more HDTV. The HD market can help drive scale for HEVC decoding, which in turn, should help reduce costs for HEVC decode silicon.  

Samsung believes it has up conversion covered. Earlier this year the company demonstrated upscaling from HD to UHD using specially developed algorithms, claiming it delivers better results than what we saw with SD to HD up-conversion. Vassilis Seferidis, Director of European Business Development at Samsung, warns: “We have to be careful because UHD is seen as the ultimate experience and you must not spoil that. Upscaling means people who bought a UHD television can enjoy as much content as possible; it is an important element in UHD.”

Seferidis says the ability of UHD televisions to upscale full HD to what he calls a very respectable ‘UHD’ experience is one of the reasons UHD sets will penetrate the market faster than HD televisions did, which is one of the key market predictions that Samsung has been making.

The increase in bit rates associated with UHD has obvious implications for storage, in the home but also in broadcaster and operator facilities. Keith Wymbs at Elemental Technologies says you need between four and six times the storage capacity for UHD even when you are in the compressed domain. “It can also make intra-production transfer more challenging.  While HEVC helps reduce the storage and transfer bottlenecks, migrating to UHD-capable infrastructure is a must,” he warns.

Harmonic’s Trow comments: “At present, quad SDI is used to achieve the necessary bandwidth over existing infrastructure. While expensive and complex to implement, this is reasonable given the proof-of-concept nature of early trials. For mass adoption as the format establishes itself, I expect next-generation Ethernet (40G or even 100G) to be applied as IT and file-based infrastructures become more prevalent in the broadcast workflow. This alleviates the connectivity constraint and moves the industry even further towards standard storage architectures.”

Trow thinks that one of the benefits of increasing storage in the production workflow would be to enable cinematic and TV workflows to be aligned much higher up the production workflow chain. He says this would reduce production costs and increase turnaround speeds.

Videonet will be publishing a new report next week that looks at the addressable market and emerging ecosystem for Ultra HD, including recent technology developments that are going to have an impact on deployment plans.  You will be able to find it here by Friday, March 14.