Reality Gap

Let’s look deeper into the case of one of the customers above, who’s actually getting much slower speeds than he thinks he is when using Netflix. This is a more common problem than you might realise, with customers of some of the UK’s biggest broadband providers regularly getting Netflix download speeds that are nowhere near the full speed of their connection.

Take a look at the graphs in figure 1, for example, which plot the regular download speeds measured from thousands of customers of BT Broadband and Sky.

As you can see, the average performance of both providers is relatively similar, with the speeds delivered dipping slightly during peak hours, as you’d expect.

Now take a look at the graphs in figure 2 – the average Netflix download speed from those same two broadband providers on the same days as before. This time the difference between the two providers is far more pronounced. While BT delivers a relatively high and consistent download performance, dipping down slightly during those evening peaks when millions of customers are binge-watching the latest series, Sky’s peak-time drop-off is much greater. Those evening peak hours turn into deep valleys in the speed graph, with average download speeds tumbling by as much as a third.

It isn’t only Sky customers who might have a problem here. Figure 3 shows the average regular download speeds from another British broadband provider, Vodafone, and the average Netflix download speeds from that same provider. Once again, average download speeds are pretty consistent – nothing that would raise alarm bells. But the Netflix speeds are a relative rollercoaster, holding up well off-peak, but plummeting during peak hours to less than half the average speed of the connection.

Still, you might be looking at that graph and thinking this isn’t a big problem. Even at its worst, an average speed of 24 Mbps is plenty for two or even three simultaneous Netflix streams within a household. But remember, they’re average figures.

Now look at figure 4, which plots the connection speeds measured from hundreds of Vodafone connections. Many are up in the 50s, 60s or 70s of Mbps, dragging that average speed up. But many are also recording peak- time speeds of less than 10 Mbps. Some are seeing speeds under which you’d struggle to maintain a single HD stream. That 72 Mbps fibre connection suddenly doesn’t look as fast as you might think.

One of the first things someone who encounters such a problem with Netflix streams might do is use an internet speed checker to test for a fault on their connection. Chances are, those internet speed tests would report that everything was fine. The customer would then spend a fruitless few hours checking home Wi-Fi equipment, or stuck on support lines, trying to figure out the reasons a speed test says they have a solid 70 Mbps connection, but they can’t stream more than 30 seconds of The Crown or The Queen’s Gambit before the video starts buffering.

So why would an ordinary internet speed test not pick up the ‘Netflix problem?’

Netflix uses ingenious methods to limit the amount of data Ultra HD streams require, but without sacrificing picture quality. In fact, Netflix can now optimise the amount of data required to stream 4K content for each individual show, and even each shot (or scene) within that show.

Previously, each title in Netflix’s catalogue would be on a “fixed- bitrate ladder”, irrespective of the show’s content. So, for example, if you wanted to watch a show at Full HD resolution (1,920 x 1,080 pixels), it required a bitrate of around 5 Mbps; to stream a show in Ultra HD (3,840 x 2,160), you’d need 16 Mbps. As we can see from the graphs above, many broadband customers would struggle to get 16 Mbps from their broadband provider when watching Netflix, putting Ultra HD content out of bounds.

Now, the bitrate required has been greatly reduced, especially for certain types of content. In a sitcom with only a few fast- moving scenes, the average bitrate needed for Ultra HD drops from 16 Mbps to around 6.5 Mbps. For some animated content that’s easier to optimise, the 4K bitrate drops to as little as 1.8 Mbps – although Netflix stresses such efficient optimisation is the exception, rather than the rule.

Overall, Netflix says that optimising content in this way has cut in half the bandwidth required to deliver Ultra HD content. The real-world impact is that most streaming sessions deliver higher quality video, according to Netflix, with customers on low-bandwidth connections who might previously have been limited to standard definition video, now at least getting Full HD (if their viewing device supports it).

The number of rebuffers – those irritating interruptions where the video pauses so it can catch up – have also dropped significantly, by 65%.