Madrid, Mexico City, Copenhague, March 1st, 2021
SAPEC: COMPRESSION TECHNIQUES OF UHD 8K VIDEO
Different Ultra High Definition content compression techniques have been tested in SAPEC laboratories for encoding of 8K resolution content with HEVC standards and existing hardware on the market.
The new 8K video format has a resolution of 7680 pixels x 4320 lines. It is therefore a format that quadruples the total number of pixels compared to 4K. Increasing the pixel density of the screen results in an improvement in the viewing experience, perceived as sharper edges, brighter colours, and increased contrast and depth.
There are already televisions on the market that support UHD 8K resolution. However, being able to cover the entire transmission chain continues to present significant challenges. At SAPEC, as a developer of solutions for the transmission of video signals, we are especially concerned with the compression of 8K content.
Currently the best option available to compress 8K video, and that offers the best compatibility between different manufacturers, is the HEVC (High Efficiency Video Coding) standard, also known as ITU H.265. As we have already mentioned, the 8K format quadruples the number of pixels compared to 4K, which implies an increase in the bandwidth requirement necessary to transmit the signal.
According to the first tests, using HEVC, the bitrate needed for 8K video transmission at optimal quality would be slightly more than double that for 4K. Thus, the required bitrate values are so high that they could exceed the maximum conditions of some live broadcast media infrastructures. These required bitrate values can be reduced if we work off-line (without real-time requirements) applying different compression techniques.
In addition to bandwidth requirements, we must also pay attention to time requirements. The strictest case being live or real-time compression, in which the compression speed must be equal to or greater than the rate of images per second.
To meet this challenge, SAPEC engineers have implemented temporal and spatial parallelization techniques offered by the HEVC standard:
- With spatial parallelization we mean dividing the image into smaller fragments so that they are processed in parallel, to later receive the result of each of the fragments and form a single output stream.
- With temporal parallelization we mean to execute the work of compression of images (or groups of images) which do not have dependencies between them, at the same time. It is also possible, especially if we work with files and the low delay is not a requirement, to divide the sequence into fragments corresponding to one or more GOPs (Group Of Pictures).
The problems that arise for compression today in terms of bandwidth and greater processing capacity requirement (although they could be solved with current tools) it is to be expected that in the close future there will be available more efficient solutions in bandwidth and required hardware cost. For this to happen we would need to wait for the launch of new compression standards such as H. 266/VVC (Versatile Video Coding) together with the improvement of the actual hardware.
8K Video Transmission
In terms of further UHD standardization by the relevant organizations, it is expected that in the coming years, this work will continue to define use cases for 8K.
SAPEC recently participated in the demonstration carried out by the Chair of Spanish Radio and Television (RTVE) at the Technical University of Madrid, where the world first broadcast of an UHD 8K signal over DVB-T2 was performed. SAPEC carried out the HEVC encoding/compressing of the 8K content that was broadcast during these tests to create a TS that could be modulated in DVB-T2. This transmission was carried out simultaneously on Cellnex (Spanish TV Operator) UHD network throughout different locations in Spain.
- Press Release about the event: https://sapec.es/sapec-cooperates-with-rtve-to-8k/
- Video (<3min) about the role of SAPEC on 8K compression (in Spanish with English subtitles): https://www.youtube.com/watch?v=ksF6RaTBqM0
SAPEC has reflected its experiences and techniques used on these tests in a document that goes into a deeper technical detail than this press release. In this technical article, can be find more information about the parallelization techniques and the bibliographic references used in this study.
Access to the Technical Article:: https://sapec.es/technical-articles/
SAPEC S.A. is a company based in Spain with commercial offices in Denmark and Mexico, which designs, develops, and manufactures reliable video contribution and distribution solutions for highly demanding Broadcast & Telecom environments. www.sapec.es / firstname.lastname@example.org