The waiting game

Due to the way streaming video works, not everyone will see exactly the same pictures at exactly the same time.

“Fundamentally, the way video distribution online works these days is you chunk the video into segments and deliver segment after segment after segment,” said Richard Cooper of the BBC. “Each segment might have a couple of seconds of video.”

Other than capacity, the biggest technological hurdle for IPTV is reducing lag, as the segments are reassembled at the receiving end.

“What you want to do ultimately is emulate broadcast and minimise the amount of time it takes from ‘glass to glass’, as they call it,” said Cooper, referring to pictures going from the TV camera to the TV screen, “so that you don’t have the circumstance where a sport alert comes through on your phone telling you who won or the goal that’s just been scored before you get to see it.”

One striking example of this was the BBC’s trial broadcasts of Wimbledon and the World Cup in 2018 in UHD, where the lag time between broadcast and the stream was often around 30 seconds.

The good news for live sport viewers is that a technological solution could soon be here, and the BBC’s R&D department was demonstrating it at trade shows before the pandemic. In one test, engineers managed to reduce the streaming latency of ordinary 1080p video to only five seconds – one second less than the six-second lag found on traditional broadcast TV.

“There’s technology out there now [that] actually allows you to chunk video up like that, but rather than having to wait for a whole full chunk to come in, you can start delivering it before you’ve got the rest of the chunk. And that takes a lot of the latency out of the chain.”

The problem might be hard to completely eliminate, however, and it may not even be wise to do so, because of a major trade-off. “The way you get around [breaks in the programme] is by maintaining a bit of a buffer in the TV, so if you get any interruptions on the network, the TV has the opportunity to fill up its buffer again, before it runs out of any video to play,” said Cooper.

Without a buffer to fill, viewers may simply be left looking at a black screen if the stream were interrupted. Imagine the tweets…