4K TV : 0.004K TV after compression

High resolution video is often cited as a driver for ultra-fast broadband. Here, for example, is Hyperoptic (a UK ISP) suggesting that if you want to watch 4K TV, you need 1 Gbps. 100 Mbps supposedly won't be enough.

A 4K TV isn't for everyone - apart from anything else it's very large, as you can see (though it isn't mandatory to install two Korean ladies with each set). However, it's certainly becoming more popular, and by 2020 over a third of West European households are expected to have a 4K set.

But what is frequently glossed over in broadband discussions is how little bandwidth is currently required for 4K TV, and how much less will be required in future. To be sure, how much bandwidth is needed for 4K is not a simple question. It depends on (at least) three things: the resolution of the video, the nature of the content and the time you have to compress it.

Uncompressed, high quality 4K can require 3 Gbps or more. However, in practice 4K is never delivered to consumers uncompressed. A compression algorithm (codec) is used to convert the raw digital video into a far smaller data stream. Many techniques are used in such algorithms. For instance, if a portion of the image is unchanged since the previous frame, the algorithm may (effectively) say 'for this portion of the screen, same again'. This requires far less data than retransmitting each pixel in that part of the screen, Or, if a large part of the image is all the same colour, then the algorithm may transmit the boundaries of the colour block, rather than separately transmitting the colour of each pixel within it.

The effectiveness of such techniques depends on many things, including the sophistication of the algorithm, the available processing power & time and the nature of the content (content with lots of movement is inherently more difficult, for instance).

However, the reduction in bandwidth is generally dramatic. Netflix, who know as much about 4K streaming as anyone, say they average 15.6 Mbps. However, sports content (which has lots of movement and must be compressed in real-time) can require more. BT's 4K Sport currently uses 20-30 Mbps.

Thus even today 4K is well within the capabilities of sub-FTTH broadband, and it is baffling that Hyperoptic think 100 Mbps is insufficient. Moreover, 4K's requirements are only going to fall. Moore's Law means we have ever more processing power to play with, which can be traded-off against bandwidth, to maintain picture quality while using fewer Mbps. In addition, processing algorithms grow ever more sophisticated. As a result, roughly 9% less bandwidth has been needed each year to support a given picture quality. Simply because video is such an important component of traffic these days, it appears as if investment in codecs is growing, meaning that the 9% rate may actually accelerate.

Companies are already claiming dramatically lower bandwidths for 4K in trials. For instance, V-Nova has reported streaming 4K at just 6 Mbps in a trial with EE (the UK's largest mobile operator). Tveon, a Canadian start-up, is even more aggressive, suggesting that with their technology 2 Mbps will be enough. (That's better than a 1000:1 compression of the raw stream).

While these claims will need to be proven out, they nonetheless suggest the potential for dramatic improvement. Indeed, even at double V-Nova's 6 Mbps, most ADSL lines would be able to support 4K TV.

Your future TV may or may not be 4K, and you may or may not be able to see the difference even if it is. However, that monster TV won't be a justification for bring fibre to your front door.