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Russia's World Cup has bene one filled with agony – but not just for losing teams and fans. People watching the tournament through live streams, instead of through TV aerials or satellite dishes, have run into problems. The BBC's iPlayer crashed during the final moments of England's clash against Sweden. Russia's World Cup has become one of the first to be streamed by millions of people. Big outages are rare but delays in streams have caused minor havoc. Games have been ruined when fans have heard others with better connections celebrating goals before they've seen them.

In some cases, streams have ranged from a few seconds behind to minutes. So, why is everyone live streaming the World Cup watching it at different times? It's complicated. The answer lies somewhere within the messy picture of internet connection speeds, devices and the technical systems broadcasters use to get recorded pictures compressed, uploaded and distributed over the internet.


Given time, the BBC, ITV and other major broadcasters, believe live streams can be made as reliable and live as traditional TV broadcasts. If successful, the result will be much higher quality audio and video than what's available right now.

The issue is latency – the amount of time between the time a video frame is recorded and when it's shown on screen. "It's a fact there is latency," says Paul Kanareck, ITV's managing director of online. "These delays we see are inherent in live streaming," adds Phil Layton, the BBC's head of broadcast and connected systems within its research and development division. "It's not something we want to live with. We're all actively trying to find ways that live TV over the internet can be broadcast as good as what people consider 'real broadcast'."

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In traditional television broadcasts, latency is limited. The bitrate – the measurement of data being transferred from one place to another – is relatively constant. A small delay happens when pictures are sent to satellites and then returned to Earth but the process is relatively stable. "The processing within the set-top box or television can add a few frames delay but there's very little in that chain where the overall latency can vary," Layton says.

When it comes to streaming live video over the internet, not just in World Cup football matches but all live streams, the picture is very different. The reason? The internet isn't constant and a lot more parts have to process the video before it arrives at smart TVs, mobile phones, or tablets. On-demand services such as BBC iPlayer, Netflix, Amazon Prime and ITV Player don't struggle with latency issues as they're not broadcasting live footage. If your Netflix series takes a little longer to start playing, it's unlikely someone screaming down the house next door or ranting on social media is going to spoil it for you.


"If you think form one end to the other, you are dealing with someone's device, their Wi-Fi connection, their mobile connection, their network connection," says ITV's Kanareck. A slower internet connection will mean a stream can be behind someone else's. "You're dealing with any number of elements before you even hit what we actually control in terms of the distribution."

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For a World Cup game to reach your phone there are multiple steps involved after the filming and editing process. There are encoders, which convert footage into digital formats; packaging software; origin servers, and content delivery networks (CDNs) that help to push digital signals out.

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"One of the tricks that was invented – this is true of any flavour of adapted streaming – in order to deal with a network whose capacity varies and latencies vary, we adopt a streamed or chunked segment delivery basis," Layton says. These chunks of video can vary in size, depending on what technologies are being used. Layton adds HTTP streaming often uses 12-second segments while others can go as small as four seconds.


During live streaming, the encoders, packagers and other technological systems collect segments. Once enough chunks have been gathered they're pushed to the next component and finally end up with the user. "They are accumulating segments and making sure they've got enough of them before they make them available to the next system," Layton says. Throughout these processes, delays can get introduced. "Each part of the chain is buffering some of them and holding some back so it doesn't think it is going to run out of them."

What you're watching a live stream on also makes a difference to how current the stream is. The receivers used by different manufacturers have "vastly different" delays, Layton adds.

ITV's Kanareck says the months of June and July have been one of the busiest periods it's had for live streams. As well as broadcasting the World Cup it's also been showing Love Island live. Kanareck says there have been two occasions where things have gone wrong. "Neither crashed the service and neither were to do with volume or surges in volume," he says.

For other broadcasters, things haven't gone quiet as smoothly. Australia's telecoms giant Optus gave up its exclusive rights to broadcast World Cup games in the country after running into streaming problems. Those trying to tune into games were suffering with outages and problems accessing its streams. The situation was deemed so severe it caused Australian prime minister Malcolm Turnbull to speak to Optus' CEO in a bid to find answers.

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But the fraught experience of live streaming a crucial World Cup match can, and will, improve. During the BBC's World Cup trial of ultra high definition (a quality that's very similar to 4K) there were bigger than usual latency issues. Layton says his tests have seen delays of between 45 seconds and 85 seconds. This is partly due to the higher quality video footage. "We've reduced this in the last week. We have a delay between our packager asking for segments and when the encoder is actually available," he says. "We pulled that delay back by 20 seconds, which has taken 20 seconds probably out of the overall chain delay."

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And there's work that can be done to reduce latency too. "Latency is going to be reduced at some point in time," says Kedar Mohite, an analyst at consultancy firm Ovum. "We're going to have a broadcast TV experience on digital but I think it is going to take some time."

Adaptive bitrate technology analyses internet speeds and provides video footage that can play on a device without needing to stop and buffer. If you have a high-speed internet connection, you can watch high quality live streams. And, in theory, if the internet speed drops during the stream, the picture should automatically drop to a lower quality. (Ideally, one that isn't noticeably worse). Elsewhere, streaming company Wowza has developed a streaming system that claims to have an ultra low latency. YouTube has also introduced an ultra low latency setting for its live streams, but it's likely most of these won't command millions of viewers in the same way that traditional broadcasters do.


At the BBC, work is ongoing on adaptive bitrates and also multicasting. The multicasting system is attempting to provide one video stream to multiple users at the same time, rather than effectively sending each World Cup match to each user as individual streams. The technique is easy to do on closed networks but on the open internet it's much harder to achieve. Layton and his teams are attempting to combine multicast technology with adaptive bitrates to further improve the reliability and timeliness of live streams.

He also hopes latency can be reduced by changing the chunks that are sent across systems. "Rather than waiting for the whole segment to be available on a server, are there ways a client can start downloading that segment before it is fully ready? If you like, trying to segment the segments."

But, for the time being, there isn't a quick fix for truly live live streams. "If you talk about the next FIFA World Cup or next Winter Olympics I think we will have a 1.5 second latency," Mohite says. "But getting it to zero is going to take another two to three more years of time."