Live 8K Contribution Considerations
Live contribution video links are professional B2B connections meant to retrieve live video feeds from the various production venues to the broadcasters, where they can be edited and prepared for delivery to the final audiences. Key constraints are pristine video quality to maintain fidelity for cascading transmissions, but also low latency.
The 8K resolution introduces a significant challenge for contribution use cases because of the sheer amount of visual information to preserve. Whereas Intra-frame video codecs, like JPEG2000, may still be used on high bandwidth fiber connections, efficient long GOP (Group of Pictures) video compression schemes will be required when bitrate needs to be kept under control, such as over satellite or unmanaged networks.
Today, a large majority of 4K satellite contributions are done with the HEVC codec in Main 10 profile (which is 4:2:0 10-bits) at 60 to 120Mbps. However, to maximize production quality, especially for HDR signal, there is also growing consideration for use of 4:2:2 chroma subsampling and sometimes even 12-bits bit depth. In the short-term, 8K contribution links can also use HEVC to leverage the maturity of the codec and the availability of ASIC-based solutions. Level 6.2 can be used for High Frame Rate if needed. Bitrates between 100 to 180Mbps can be considered. Over time, to reduce cost and deploy more and more 8K services, it will be beneficial to consider migrating to a new generation codec like VVC, and bitrates below 100Mbps seem achievable.
Dedicated hardware solutions based on FPGA or ASIC acceleration can bring tremendous performance for use cases with massive processing requirements like 8K. On the consumer side, this is usually the clear way to go (playback/display).
For professional encoders and decoders though, using a SW-based solution based on COTS servers brings a lot of benefits in terms of flexibility, including cloud migration options, where it is feasible to deploy the processing resource. Dedicated ASIC-based encoders are an alternative that offer much smaller and more transportable equipment options that may suit better for certain scenarios.
Flexibility will be very important to grow the 8K services supply alongside the demand. In particular, it will involve providing significant incremental video compression gains over time to reduce delivery costs. The ability to increase bit depth if needed, offer 4:2:2 subsampling, and adjust various video processing steps like watermarking will be desirable. Proposing a straightforward and economical migration path to new codecs like VVC will also be key, just like HEVC proved essential for widespread 4K adoption.
As of today, typical contribution latency is around 700ms and similar values can be expected over time for 8K. Professional video links have a much lower latency than final deliveries to end users, especially Over-the-Top (OTT) ones even if recent years showed significant reduction of OTT latencies.
This can explain why 4K contribution deployments usually did not have ultra-low latency targets (but still much lower than any OTT deliveries). 8K can reasonably be expected to follow the same path.
Early 8K adopters can combine four UHD satellite contribution links, but this involves interoperability challenges and can introduce quality impact with quadrant borders becoming visible. Transponder bonding can also be considered, but DVB-S2X modulation allows significant capacity gains over previous generation, which can be leveraged for 8K transmission on a single transponder.
Around 200Mbps are available and using that capacity for an HEVC 8K 4:2:2 contribution encode is already possible today. As a reference point on an adjacent use case, 8K satellite distribution by NHK in Japan has been a reality since 2018. Doing this monopolizes a full satellite transponder for a single channel. However, while possible for some initial services, is not very scalable economically. Being able to transition over time to a new generation codec like VVC to drive bitrate down and free up transponder space appears to be an elegant solution to this problem.
Wherever satellite contribution links are not available, contribution over IP is still an option. Since live HEVC Encoders can generate live 8K 4:2:2 streams in 180 – 250Mbit/s range, transport to and over global CDNs like Akamai, Amazon or Cloudfront can be arranged. Alongside managed networks, there is a growing usage of the public Internet to contribute content.
This allows cheaper backup links of course. It also enables many primary links for smaller scale events. It is also useful for temporary events that cannot justify a full setup, or for events which span a large zone or are unpredictable in nature.
When event venues are sufficiently connected, contribution links can also consider the use of dark fiber leased from telco operators. Such large fiber bandwidth typically allows the use of intra-based compressions format like JPEG 2000 and JPEG XS, because the increased bitrate is not an issue.
Remote production using SDI over IP can be considered, for example using SMPTE ST 2022-6 Transport of High Bit Rate Media Signals over IP Networks (HBRMT). More complex use cases requiring an orchestrator but allowing individual breakouts can even use SMPTE ST 2110-20 Professional Media Over Managed IP Networks: Uncompressed Active Video. However, transport of uncompressed 8K means the bitrates are rapidly getting impracticable and some form of compression is desirable, such as using ST 2110-22 Professional Media Over Managed IP Networks: Constant Bit-Rate Compressed Video.
8K and 4K are already getting more widespread in capture devices, undeniably driving up the bitrate requirements. This is where 5G can be a gamechanger and accelerate 8K adoption by massively improving uplink and downlink network capacity thereby increasing content supply and demand opportunities (link to 5G distribution page).
The use of 5G and 8K for contribution will likely benefit from the highest bandwidth mmWave capability at the transmit and receive end of the contribution link. Private 5G networks to cover specific sites or events can avoid the contention and security issues relating to using public networks. Technically, to secure enough reliability, 5G will also likely be combined with Automatic Repeat Query streaming methods such as VSF RIST