iPlayer beta low latency trial enters new phase

We’re expanding our low latency streaming trial on BBC iPlayer beta, increasing the number of supported devices and extending the testing period. This next phase will allow us to measure more precisely how well low latency streaming performs outside of our lab and in people’s homes, across different networks and conditions. It’ll also help us to understand what it takes to deliver live content online as fast and reliably as broadcast. Senior R&D Engineer Melissa Darragh writes with details of the extension of the trial.

Streaming has fundamentally changed how audiences consume live content. Yet, despite the growth in popularity of internet delivery, traditional broadcast still offers the fastest end-to-end experience. For live events and content highly popular on social media, the difference in delay becomes more noticeable, and more important.

At BBC Research & Development, we have been exploring how we can reduce streaming latency while maintaining the quality and reliability our audiences expect. Over the past year, we have been developing means of delivering our low latency streams via BBC iPlayer to prove the feasibility of low latency streaming to the home. Initially, this was limited to a small subset of devices to refine our data collection and prove that the delivery of the stream worked in a real-world environment.

The results we have gathered throughout this initial phase have been encouraging, demonstrating that the performance of the low latency streams has been largely similar to conventional streams. However, there are more complex factors such as Wi-Fi connectivity, ISP congestion and variations between devices that have a significant impact on the reliability of streams. To really understand behaviour under those realities, we need to extend the trial to more devices and run it for a longer period.

As of this week, we’re entering a new phase designed to broaden device support and extend the hours of operation. This is so we can reach more reliable conclusions about how low latency streams behave in the home, at scale. This will also increase participation from homes with different internet service providers, Wi-Fi setups, and network stress patterns. Low latency puts the player closer to the ‘edge’ of what the network can support; so, diversity in real-world conditions really matters.

Extending when the trial is available lets us capture performance through different live moments such as sports, music, or breaking news, as well as across weekdays and weekends. This will result in a larger and richer dataset, which will allow us to measure smaller differences in performance.

Working with the teams responsible for our TV iPlayer product, we have once again arranged for a low latency stream to be available via iPlayer beta.

The new phase of our trial aims to explore device compatibility a little more by including a wider range of TV and streaming device models. Some of these are yet to fully support the behaviour described previously whereby a TV that has started behind the target latency or has subsequently fallen behind can play slightly faster than normal speed to catch up. Whilst this capability is necessary to achieve a consistent low latency, we have temporarily extended the trial to TVs that can't yet do this. Although the latency will not be quite as low as for those devices that can catch up, we will get valuable data on how other aspects of low latency streaming perform.

Low latency shouldn’t mean fragile. It should mean timely and reliable. This research is an important step along the way to getting there. However, more work is needed before we could deliver a fully resilient fault tolerant low latency stream at the scale needed for a major sporting event.

If you’re on a supported device (see list below) and would like to get involved, switch on iPlayer Beta and watch BBC Two live – the trial stream is currently available from 8am – 10pm BST for viewers who have set their location to England or Scotland. It is expected to run for around a month.

Other than the reduced delay, we don’t expect that you will notice any significant differences when watching this stream. However, if you experience any issues, you can revert to a conventional stream by opting out of iPlayer beta via the Settings menu.

If your TV is not yet included, watch this space: more devices are on the way as we scale up the trial in the weeks to come.

Devices currently included in the low latency trial: