BBC trials low-latency live streams during Glastonbury and Wimbledon
The BBC has taken its trial of Low Latency DASH with chunked CMAF segments to the next stage by assessing how well its approach performs when received by viewers watching marquee sports and music events on iPlayer at home.
The trial, which is for select viewers of BBC Two viewed live on iPlayer, will likely include music festival Glastonbury, tennis championship Wimbledon and the Women’s soccer Euros which all start by the end of June or beginning of July.
Maintaining High QoE
The end-to-end delay on content streamed over iPlayer is currently around 40 seconds, versus the 8-10 seconds of broadcast channels--a “significant difference,” according to BBC’s Lead R&D engineer Chris Poole in a blog post. “For some content, viewers may not notice, but for live sport and for live events with a social media following, delays can detract from the viewing experience. We aim to address these delays whilst maintaining a high QoE through our work on ‘low latency streaming’.”
BBC R&D will use performance data from the low-latency streaming sessions to get a “detailed understanding of how the quality and reliability compares with its traditional live streaming in a wide range of real homes.” If this goes well, it will then move to fine-tuning the stream and testing different variants, aiming to maximise reliability.
Device Support and Trial Expansion
Among considerations are what should happen if users do experience some rebuffering. “Should the stream just resume, leaving them further behind for the rest of the programme? Should the stream catch up, skipping a few seconds in the process? Neither is ideal.”
Instead, the trial stream will play slightly faster after a stall, aiming to maintain low latency but without the viewer missing any of the action. That means it will start the trial using only devices that support variable speed playback capability and will maintain the target latency it has set. These include third-generation Amazon FireTV Stick, second-generation FireTV Stick 4K, and Samsung CU8000 and CU8500 TVs. More devices will be added during the trial.
“We are starting small but hope to expand the trial as we gain confidence in its performance,” Poole says. “We also hope to gain a better understanding of the scenarios under which low latency does not work so well, and whether we could avoid offering a low latency stream to those less likely to benefit.”
This is only a first step in trialling low-latency streaming to the public. The BBC warns that viewers should not expect that all live internet viewing will match the timeliness of broadcast at the end of the trial. Gradual improvements are more likely.
According to Poole, “More work is needed to build a fully resilient, fault-tolerant system that can scale to the size of audience that the BBC serves for major sporting events. Since common ways to build in resilience to failure themselves add delay, achieving this for low latency streams remains a challenge.”
Related Articles
Moves to transition the UK's free-to-air broadcasters to an all-streaming future have gathered pace with 2035 a likely tipping point with the BBC leading the charge.
15 May 2025
The BBC has outlined how it will plan future R&D and it is being built around internet-only, intelligent, intermediated, interactive and immersive media.
16 Apr 2025
The BBC is preparing to shut down its traditional television and radio broadcasts and shift everything online, but will do so only if the principal of universal affordable access is maintained.
12 Dec 2022