As part of its September 2017 product unveiling event, Apple finally announced a follow-up to its fourth generation Apple TV with an enhanced model.

Called Apple TV 4K, the new set-top box will be available from 22 September in two storage sizes: 32GB and 64GB. It is priced at a premium over the existing HD Apple TV model because it supports both ultra high resolution video and high dynamic range.

So here's everything you need to know about the Apple TV 4K.

Apple TV is a set-top-box that you can hook up to your TV to access video apps and streaming services. It was originally labeled a hobby device, but by 2015, Apple CEO Tim Cook revealed that 25 million units had been sold.

In late 2015, it released a fourth generation model with Siri, a trackpad remote, new operating system called tvOS, an app store, and two different storage capacities. But it didn't support Ultra HD (4K) content or high dynamic range (HDR) content - both technologies that rivals offer.

Now Apple has joined the fray with a device that looks like the older version, but with a faster processor and 4K HDR video support.

After months of speculation, Apple officially announced the new version of its Apple TV box, which will be sold alongside the existing model.

It adds 4K HDR video to the mix, being able to play films and streamed content through services such as Netflix, Amazon Video and Apple's own iTunes in the very best format possible. The box will support Dolby Vision and HDR10 formats. Apple has also confirmed that the devices menus will also be in 4K. The boxes fly over screen savers have also been updated to 4K HRD footage. 

The new set-top-box features a faster processor. The current Apple TV uses the A8 chip, which was launched alongside the iPhone 6 and iPhone 6 Plus in 2014, but that isn't capable of 4K video playback.

Instead, Apple has now added the A10X Fusion processor, as found in the latest iPad Pro models. That, and a bump up to 3GB of RAM, should easily handle 4K HDR footage.

Indeed, Apple claims it is twice as fast, with four times the graphical processing power something it is keen to show off with new games like Sky, demoed on stage at the products launch. 

The Apple TV 4K will come with the latest software, tvOS 11.

Like with the existing Apple TV, the Apple TV 4K comes with a voice remote that has a touch panel at the top. This not only enables users to navigate easily, they can also use voice commands to play and search for content.

In a move to encourage people to experience the benefits of 4K and 4K HDR content as quickly and easily as possible, Apple will automatically update and HD movie purchase for free. The move should mean that if you’ve bought Lego Batman in HD you’ll automatically be able to watch it in 4K.

The new Apple TV 4K box will be available for pre-order on 15 September and will shop from 22 September.

The existing Full HD Apple TV will continue to be available too.

Prices start at £149 for the 32GB Apple TV (2015). The Apple TV 4K 32GB model costs £179, while the 64GB version will set you back £199.