BBC iPlayer launches low latency streaming trial

The BBC has launched the first phase of a trial of low latency live streaming on BBC iPlayer.

For the next few weeks, viewers using selected devices who have opted into iPlayer’s ‘beta’ mode may see an experimental low latency stream of BBC2 when watching live on iPlayer.

There’s currently a delay of around 40-seconds for everything streamed on iPlayer, compared to a end-to-end delay of only around 8-10 seconds for traditional TV broadcasts.

For live sport and for live events, this 30-second difference in delay between streaming and TV can be frustrating for viewers.

The BBC (through its R&D department) is attempting to address this delay whille maintaining a high quality of experience.

Reducing internet delivery delays to match traditional broadcast means less time for the streaming client to adapt to changes in network conditions. This in turn makes it harder to avoid ‘stalling’ where video playback stops and viewers have to wait for a period of ‘rebuffering’ before the stream continues.

BBC R&D has worked on ways to solve this and have modelled, tested and analysed the performance. It’s using a technology called Low Latency DASH with chunked CMAF segments. The aim is to achieve delays in streaming that are comparable to broadcast.

To trial the changes in the real-world, some viewers of BBC2 on iPlayer will be able to see a low latency stream. The BBC will then use performance data from these 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, the broadcaster says it will then move on to fine tuning the stream and testing some different variants, to maximise reliability.

During the trial, if viewers experience some rebuffering, the trial stream will play slightly faster after a stall, aiming to maintain low latency but without the viewer missing any of the action.

Doing this without the viewer being aware requires some functionality that is not available on all TVs, so the trial is only taking place using devices that support this variable speed playback capability.

The first device models for the trial are 3rd generation Amazon FireTV Stick, 2nd generation Amazon FireTV Stick 4K, and Samsung CU8000 and CU8500 TVs. The BBC will then add more devices during the trial.

This trial is only our first step in trialling low latency streaming to the public, says the BBC, and adds that viewers shouldn’t expect all live internet viewing will match the delays on broadcast at the end of the trial.