Considerations in Transporting 8K to End Users
The 8K format was popularized by CE-display manufacturers and the Japanese broadcaster NHK – all paving the way to broadcast the 2020 Tokyo Olympics in 8K. With more and more 8K content becoming available, the usage of new codecs combined with latest transmission systems (e.g. DVB-T2/S2, ATSC-3.0, 5G-Broadcast) offers the prospect of generalizing the distribution of 8K to end users.
Example 8K distribution bitstream formats include 7680×4320 resolution, 50/59.94fps framerate, 10-bits bit depth, PQ/HLG high dynamic range, and BT.2020 color space. To maintain an optimal quality of experience, 8K HEVC encoding typically requires over 50Mbps which remains prohibitive in many transmission scenarios, but seems to be changing rapidly with 1Gbps service to consumers becoming more common.
However, while HEVC was used for most 8K deliveries in the past years, new codecs emerged recently in the video codec landscape offering perspectives below 35Mbps. On the MPEG side, VVC, EVC and LC-EVC were developed for different use-cases and applications. The Alliance for Open Media (AOM) was created and developed AV1. The Audio and Video Coding Standard Workgroup of China (AVS) developed the AVS3 codec, with 8K as the targeted application.
- VVC has been jointly developed by ISO/IEC and ITU-T as successor of HEVC, implementing tools and features making it capable of addressing a wide range of use-cases and applications (8K, 360, HDR). The Media Coding Industry Forum (MC-IF) has been initiated to monitor the development of VVC and reduce the risk of licensing issues.
- EVC has been developed in parallel to VVC in MPEG solely, pursuing the goal of developing a two-approaches codec: A patent-expired, thus royalty-free, baseline providing performance close to HEVC on one side; Plus an advanced profile implementing switchable tools with substantial coding gain over HEVC on the other. EVC proponents committed to publish FRAND licensing terms for the advanced profile in the two years following FDIS publication in April 2020.
- LC-EVC has been developed to provide a manner of delivering new video formats leveraging existing codecs used as a base-layer with the constraint of having half the resolution both vertically and horizontally. For example, LC-EVC can provide an 8K enhancement layer on top of HEVC-4K bitstream.
- AV1 development was initially conducted with a focus on file use cases rather than stream-oriented, both in terms of complexity and encapsulation. AV1 was designed to be royalty free. In terms of performance, AV1 is competitive with HEVC, even better in some cases. It also provides unique normative features such as film grain synthesis.
- AVS3 was developed by AVS and is intended to outperform HEVC in terms of performance.
To reduce cost and power consumption to decode 8K, consumer devices will typically embed dedicated hardware solutions based on FPGA or ASIC acceleration. To encode 8K in professional settings, it can make sense to use similar HW acceleration, like FPGA or ASIC but also custom CPU or GPU solutions, just to cope with the massive processing requirements.
However, using software running on Commercial Off The Shelf (COTS) hardware offers more flexibility. It can facilitate faster service launches using cloud computing resources. It also allows significant incremental compression gains as the technology matures, providing crucial cost advantage to scale 8K delivery to the masses. Finally, it enables supporting multiple formats— which is increasingly important in a rapidly changing ecosystem.
The 8K Association will soon issue a report on the state of encoder and decoder development.
For live streaming, low latency is crucial to maintain some parity with alternative transmission options. 8K distribution compression latency requirements are expected to be around one second, similar to current 4K ones.
It’s worth noting that end-to-end latency became a renewed area of focus over the last few years in the industry when comparing streaming to cable, IPTV, satellite and terrestrial deliveries. However, the bulk of the optimizations is on the encapsulation and transport side more than on the compression itself. As such, 8K in itself is not expected to fundamentally impact the delivery chain latency, which is good news for its adoption on live events.
8K streaming is nothing new: YouTube launched 8K support back in June 2015 – in VP9 at first, and then in AV1 in 2020. Since then more and more OTT platforms are introducing 8K like Rakuten TV, The Explorers or NASA.
The barrier of entry for an 8K service in OTT is lower than on more traditional media, and with an increasingly significant 8K TV market share, there is growing incentive to launch such services.
The challenge is to scale such services in a commercially profitable way – which is where efficient video compression can help by reducing delivery costs. Real-time processing will also become necessary for live events coverage like premium sports. Longer term, Dynamic Resolution Encoding (DRE) could be leveraged to only deliver 8K bandwidth for scenes where the extras resolution makes a difference. Additionally, AI encoding techniques and scene-based encoding and segmenting also promise to reduce file sizes and needed bandwidths for 8K content.
Recent cable and IPTV set-top boxes are often capable of supporting premium use cases like UHD, HDR, and Next Generation Audio (NGA). 8K is now becoming the next frontier, but some questions remain on appropriate codec(s) and exact use cases that the different streaming experiences on connected TVs will likely answer in the next few years.
Fiber backbones and cable distribution architectures are expanding in ways which will make 10 Gbps distribution nodes a reality. This is already enabling service up to 1Gbps to homes today opening up the ability to begin to deliver 8K content in limited geographies
5G deployment represents a massive opportunity for 8K delivery. Fixed Wireless Access (FWA) is the use of a mobile network for the last mile to deliver broadband connectivity at home with the help of a Customer-Premises Equipment (CPE).
By benefiting from the latest enhancements designed in the enhanced Mobile Broadband (eMBB) scope of work of 3GPP, including beamforming, massive MIMO and support of mmWave frequencies, 5G FWA can provide bandwidth capacities competing with optical fiber with significantly lower deployment costs. This makes 5G FWA particularly suitable to emerging markets and rural areas where wireline broadband connectivity is not prevalent. The number of FWA connections is forecasted to exceed 180 millions by the end of 2026 (Ericsson Mobility report), serving approximately 650 millions individuals, able to consume 8K services.
eMBMS is a point-to-multipoint LTE interface used to deliver broadcast services to mobile devices. Significant improvements, designated as enhanced TV (enTV) or feMBMS were brought by 3GPP in releases 14 and 16. Addressing all the requirements of a 5G broadcast system, feMBMS has been profiled by the ETSI under the term LTE-based 5G broadcast (TS 103 720). In particular, feMBMS allows the deployment of dedicated broadcast cells, potentially reusing the infrastructure and the frequencies of existing terrestrial broadcast networks. A second multicast and broadcast capability is expected for release 17, referred to as 5MBS (5G Multicast/Broadcast Services), targeting the coexistence of unicast and multicast/broadcast capacities within a same carrier. Based on 5G NR (New Radio), it is particularly suitable for use-cases where broadcast/multicast services are expected to be delivered to a limited number of cells due to user interests and the concerned cells may dynamically change due to user movement.
The key takeaway: both these broadcast capabilities may be exploited to offer an extended coverage of 8K live services.
Over the Air
ATSC 3.0 and DVB provide the main standards for Over-the-Air (OTA) distribution of video content. These are bandwidth-limited networks where both new codecs and the use dual-layer schemes will likely be needed to distribute 8K content.
For example, Brazil is currently developing their new terrestrial TV 3.0 scheme and suggesting 4K be sent over the air while an additional layer would be sent Over-the-Top (OTT). Once the content is decoded, it will be reconstructed to 8K by the receiver, which will likely be located inside the 8K TV
DVB is still at the commercial stage for considering a dual-layer scheme as part of the DVB specification for Next Generation Codecs.
Korean research institute ETRI has also shown three possible ways to enable the delivery of 8K content over an ATSC 3.0 system here and here. One is to use a similar approach using Scalable HEVC (SHVC) to transmit 8K. ATSC 3.0 has also started to consider VVC as a new codec, meaning the presented concept could, over time, be extended to scalable VVC also. The second way is to bond two channels (UHF and VHF, for example) to achieve the approximately 110 Mbps capacity needed. The third method uses the Multiple-Input-Multiple-Output (MIMO) capability of the ATSC 3.0 standard. Here, the idea is to use a single RF channel but increase the bandwidth by using a two-antenna solution.
In an NAB pilot presentation, a base and enhancement layer used the VVC codec to illustrate this potential. You can view this presentation of the project here.
All this activity suggests that OTA may become viable for 8K distribution, but it will take time.
The most notable example of 8K satellite distribution is the NHK satellite deployment in Japan that started in December 2018. Direct-to-Home (DTH) was the first delivery method compatible with 8K HEVC encoding requirements.
It was demonstrated that a complete 36MHz transponder can host a single 8K channel. This model is difficult to scale economically though as satellite transponder bandwidth is precious.
Using a new generation codec like VVC or a dual-layer approach would alleviate this problem. Backward compatibility is also traditionally a major concern for satellite delivery, so a hybrid solution might also be considered, where a 4K link could be completed, e.g. by joint metadata to guide upsampling, or a second layer delivered independently.
While often overlooked, Satellite, just like OTA, is still actively used for VOD deliveries using local storage on Customer-Premises Equipment (CPE). With more 8K cinematic content now becoming available, VOD could prove to be a valid use case for 8K over satellite.