From a picture quality perspective, it is likely that the quality of OTT video is already as good as, if not better than, broadcast quality. Where linear channels have not invested in or completed digital transformation projects yet, OTT will be exceeding it already.
BT Sport, arguably the world’s most technically progressive broadcaster, needs to reach its audience across multiple screens and currently has a baseline production format for producing live sports content in UHD 4K with Dolby Atmos sound and High Dynamic Range (HDR). It distributes different versions of the broadcast that retain the best audio-visual quality formatted for different devices. Subscribers to the premium BT app will be able to view UHD 4K HDR 5.1 on their smart TV or smartphone although HD HDR is considered by BT Sport to be the ideal format to mobile (the smaller screen nullifying any advantage to displaying greater resolution or surround sound).
Looking ahead, it is trailing master capture at 8K UHD which will not only increase downstream picture quality of HD or UHD streams but be ready for when 8K distribution becomes commercially viable. Even then, HD HDR may still be the optimum format for mobile.
BT Sport and France Télévisions (with EE and Orange mobile operators respectively) have also trialled 8K workflows for applications including live VR consumer experiences which will be made possible over 5G networks.
However, picture quality is not the only measure by which consumers judge live streamed content. It is the overall quality of experience of the event where the focus is today and here OTT providers are under pressure to deliver.
In particular, reducing latency and removing rebuffering issues, while maintaining high bitrates throughout the event, regardless of where the user is and what device they are watching on, are critical issues to solve in order to maintain user satisfaction.
The steps involved in the end-to-end streaming transmission result in latency of over a minute (or more) compared with linear broadcast. Viewers are increasingly intolerant of this gap which is particularly glaring during mass viewing of live events like a World Cup match where goals may be celebrated by viewers of the TV broadcast significantly ahead of those watching the same feed streamed to a device. Such latency also makes live synchronised second viewing apps impossible.
Solutions are being developed to address this at standards level. Developers of the Common Media Application Format (CMAF) which include Apple and Microsoft, are targeting live low latency and Standards body DVB is working on a low latency mode within DVB-I, a new open standards-based approach to OTT and broadband television.
Low latency requires encoders, packagers, CDN and video players to be updated to deliver end-to-end latency targets. Achieving this consistently across multiple devices and platforms takes the complexity to another level, increasing time-to-market. The most realistic and achievable goal is latency of less than 5 seconds – at least in the short-term when it comes to scalable events, according to codec developer Bitmovin.
Other issues impacting QoS including managing peaks in demand which in turn require an operator’s platform to have the necessary network and peak-load capacity in key areas, such as authentication, authorisation, licence delivery and CDN playout.
That this remains a challenge was evident in a recent high-profile outage by New Zealand ISP Spark at the start of its coverage of the Rugby World Cup. Complaints ranged from freezing, lagging and glitching during the first 20 minutes of the opening ceremony – to differences in streaming quality and significant delays.
