What causes buffering?

The question ‘what causes buffering’ is often asked – but only usually once it’s already happened…

Monday, 4 September, 2023

It’s a familiar scenario.

You settle down on the sofa/bed/chair in front of a Netflix film/a YouTube clip/a pre-recorded Teams call.

All is well, until a frozen picture and a small spinning circle indicate a sudden service interruption.

These momentary (if you’re lucky) hiccups are the most obvious manifestation of a process known as buffering.

Despite constantly taking place, buffering shouldn’t be noticeable in normal conditions.

When it does become evident, it’s usually because your internet connection isn’t fast enough.

So what causes buffering, and what mitigates or minimises it?

Hitting the buffers

If you’ve always thought buffering only occurs in train stations, you need to get out less.

Buffering is an integral component of streaming – when an audio/visual file is played over the internet, rather than being downloaded onto your device as a complete file beforehand.

If you wanted to watch an episode of The Crown in HD, its total size would be almost half a gigabyte.

Downloading this would take ages, so Netflix – and all other streaming services – only download a small portion at a time.

As you watch the first few seconds of footage, the next few seconds is being pre-loaded in advance, in the background. This minimises the delay before playback can commence.

(Live footage is slightly different because it’s arriving as the broadcast is taking place, rather than from a data server.)

What causes buffering problems to arise?

In an ideal world, the endless chain of data parcels containing the next segment of footage ought to arrive seamlessly, in the highest definition your internet connection can support.

If there’s a momentary drop in available broadband line speeds, protocols swing into place which automatically lower the file size (and picture quality) of individual segments.

You might notice this when a stream starts, with pixellation gradually diminishing during the initial seconds of playback. If it happens mid-stream, there’s a bigger problem.

If even variable bitrates can’t maintain an unbroken stream, it will reach the end of its received segments and freeze until the next content block is downloaded.

There are other provider-led solutions which could mitigate matters, but we won’t explore the technicalities of scalable server architecture or orchestration logic here.

Can I do anything at my side?

Occasionally, issues relate to an overloaded server or a supplier failure. However, buffering is more commonly caused by domestic internet connections not being quick enough.

If you’re on an 11Mbps Fibre to the Cabinet line, and full fibre broadband isn’t an option, you’re inevitably going to face some issues, especially at peak times like the internet rush hour.

However, these steps should help to minimise the prevalence of buffering:

  1. Always watch footage in standard definition. An SD file is around a third the size of an HD one, slashing data transfer volumes and reducing pressure on your connection.
  2. Hardwire devices to your router. We’ve previously explained why an Ethernet cable is faster than WiFi. If your router and device are in different rooms, invest in Powerline adaptors.
  3. Only stream on one device at a time over a slow connection. If your kids are watching the latest Grand Tour episode on Amazon, don’t try to run iPlayer at the same time.

Finally, don’t assume you can simply wait a few minutes to give the file extra time to download.

The just-in-time nature of streaming means future segments won’t be summoned, unless you’re downloading and saving the file onto a local device rather than merely streaming it.

Neil Cumins author picture


Neil is our resident tech expert. He's written guides on loads of broadband head-scratchers and is determined to solve all your technology problems!