4K, Ultra HD, 4K Ultra HD – call it what you want, the 'four times HD' TV technology is here to stay. (Until, of course, it's inevitably leapfrogged by 8K – but we're sure that's some way off.)
The TV market is awash with 4K models; Ultra HD Blu-ray players (and discs) are rising in number and dropping in price - even the latest Xbox One X has one built-in; and we now have not one but two ways of watching 4K broadcasts courtesy of BT and Sky. Of course, you can also stream 4K content from Amazon, Netflix, iTunes, YouTube and more.
Over the last few years, many, many Ultra HD TVs have passed through our test rooms, including more and more 4K OLED TVs, from the likes of LG, Sony, Panasonic, B&O and Toshiba, delivering what is (arguably) the ultimate TV performance.
So, what's 4K TV all about? On this page we'll run through the basics of ultra high-definition video, and get you up-to-date with the latest 4K news and available content.
MORE: 4K content guide
What is 4K Ultra HD?
Officially, 4K resolution is 4096 x 2160 pixels. However, in order to shoehorn this higher resolution video on to a normal 16:9 picture format, it has been altered to 3840 x 2160 – still four times the total number of pixels found on a Full HD 1080p screen (1920 x 1080).
In order to take full advantage of 4K Ultra HD you will, of course, need a compatible TV, a compatible source and the 4K content that packs those all-important extra pixels.
And that had been the hold up. While we've been reviewing 4K TVs since 2012, it's only really the last couple of years or so that we've had any Ultra HD content to get our teeth into. So if you've resisted 4K until now, you may have made the right decision - but now is a good time to think about taking the plunge.
MORE: Best budget 4K TVs
What about HDR?
‘HDR’ stands for High Dynamic Range, and is currently the Big Thing in the TV world. The term originates in photography, and refers to a technique that heightens a picture’s dynamic range – the contrast between the brightest whites and the darkest blacks. The theory is that the higher the dynamic range, the closer a picture gets to real life. HDR for televisions is basically the same idea.
An HDR TV is all about contrast and colour performance, and a TV must be able to deliver a certain level of brightness and black level to support HDR. The most readily available spec comes courtesy of the Ultra HD Premium badge, which requires that a TV delivers 4K resolution (3840 x 2160), 10-bit colour depth, BT.2020 colour space representation and, naturally, support for HDR video. This badge therefore claims to ensure the 'ultimate 4K performance'.
And its delivery would be simple were it not for several competing HDR formats - because tech just loves a format war! Alongside HDR10 and Dolby Vision, the two most prevalent formats, which can be found on Ultra HD Blu-ray discs, Amazon, Netflix and iTunes, and there is also the Samsung and Panasonic-backed HDR10+ format and Hybrid Log Gamma (HLG), which is intended for HDR broadcasts.
Still, HDR is getting out there - and not just on TVs and AV-related sources. Samsung's Galaxy Note 7 (you know, the one that blew up) became the first smartphone to support HDR video, and it has since been joined by other handsets, including the LG G6 and the Galaxy Note 8, LG V30. Even the iPhone X supports Dolby Vision.
MORE: 10 of the best HDR TVs
How can you watch 4K video?
To watch 4K video you need a 4K screen, a 4K source and 4K content. The good news is your options have increased exponentially in the last couple of years.
Then you need a source. This can now be as simple as an app - Amazon, Netflix and YouTube all offer streaming 4K content, not only on 4K TVs and 4K Blu-ray players but also on 4K streaming boxes such as the Amazon Fire TV and Google Chromecast Ultra. Apple's latest streaming box, the Apple TV 4K, can stream 4K HDR content (HDR10 and Dolby Vision) from iTunes where available.
For broadcast 4K TV, you'll need the relevant box - for now that means either the BT 4K box for the BT Sport Ultra HD channel or a Sky Q box for Sky Ultra HD. There's also a 4K Virgin box, but sadly there isn't actually any 4K content available.
Want to play discs? Then you, of course, need a 4K Blu-ray player - we'd point you towards the Sony UBP-X800 and Oppo UDP-203 – and some Ultra HD Blu-ray discs, which are growing in number all the time.
More after the break
How can you stream 4K video?
Netflix 4K streaming arrived in 2014, with House of Cards: Season 2 making history as the first 4K content streamed by the service, with Breaking Bad in 4K following soon after. There are now over 100 titles, including Black Mirror, Daredevil, Narcos, Marco Polo and Stranger Things. Naturally, more content – mainly original – is being added all the time.
To watch Netflix 4K you will need a 4K TV that supports the HEVC codec that Netflix is using in order to play the content, which is pretty much all 4K TVs brought out by the big brands since 2016. You'll find the necessary 4K content on your compatible TV's Netflix app.
Amazon's 4K content comprises mainly TV shows, such as The Man in the High Castle, Red Oaks and Transparent, and these are available to stream for free for subscribers of the shopping goliath's Prime Video service. Other TV shows, as well as films, are available to stream in 4K, but for a fee.
And compared to Netflix, fewer 4K TVs have the Amazon Prime Video app.
YouTube also has a selection of 4K videos, but unless you're watching on a 4K TV, you'll need to make sure you have a compatible 4K monitor. YouTube uses the VP9 codec developed by Google, and it's been running in the Chrome browswer since 2013. As with HEVC, you'll need to make sure your TV or monitor support VP9 before trying to stream. For those who have the required hardware, there's even an 8K video.
What about 4K media streamers?
4K media streamers are now on the market, too, and the UHD Alliance has recently brought them under its UHD Premium umbrella.
The Amazon 4K Fire TV box delivers Ultra HD content from Amazon's own selection on Prime Video and from Netflix. The Roku Ultra offers a similar proposition, while Google's Chromecast Ultra and Sony's PS4 Pro games console only offer 4K content from Netflix and YouTube.
As you can tell from the name, the Apple TV 4K can stream Ultra HD content which you can now find on Apple's iTunes store. It's also available in HDR (either HDR10 or Dolby Vision where available).
MORE: 4K content guide
Can you watch 4K broadcasts on TV?
The road to 4K broadcasts has been a long one but we do now have two options: BT Sport Ultra HD and Sky Ultra HD. Both offer live 4K sport - mostly football – to owners of their flagship set-top boxes. Sky also has 4K TV shows, from dramas to natural history programmes, plus movies via its on-demand service.
Previously, the BBC said it planned to broadcast 4K as standard by 2016, but that never happened. And, until recently, the only 4K content we'd seen from the Beeb was a four-minute clip of Planet Earth II on iPlayer.
In December 2017, the BBC launched a 30-day trial where owners of compatible TVs could stream its Blue Planet II series in 4K (and HDR) through the BBC iPlayer.
The BBC and Sky are also part of the UHD-Forum, which has been formed to promote 4K TV. Led by the Digital TV Group, the forum aims to avoid the confusion that emerged when HD TV and HD-Ready TVs first came on sale.
As ever, it seems that Japan is way ahead of us with 8K broadcasts...
Ultra HD Blu-ray discs
Ultra HD Blu-ray became official over two years ago, and it's since picked up steam, with most major Hollywood studios - even Disney - now behind the format. It's a good job really, considering the increasing number (and affordability) of 4K Ultra HD Blu-ray players on the market.
Well over 100 titles from Warner Bros., 20th Century Fox and Sony Pictures are now available around the world and in the UK, with that list continually growing. In fact, all the 4K discs on sale and coming soon can be found in our round-up here.
The majority of discs on the market feature HDR10, however more titles are getting the Dolby Vision HDR treatment.
How much does a 4K TV cost?
With the lion's share of big brands' TV line-ups comprising 4K sets, there's a good chance that when you buy your next TV it will be a 4K screen whether you like it or not.
To make the most of Ultra HD, we wouldn't recommend using anything too small, but a much wider choice in both screen size and price can only be a good thing for the technology.
Of course, if you want to break the bank, you can. Your average 65in OLED sits in the £3000-5000 ballpark, but you can pick up a 2017 OLED from LG for just £1500. Any OLED bigger than 65in and you're looking at a five-figure sum.
But don't let those huge TVs deter you. 4K TVs in realistic sizes and at realistic prices are now available.
MORE: Best budget 4K TVs
4K TV verdict
If you previously doubted whether 4K would ever make the breakthrough into the mainstream - and we wouldn't have blamed you - it does now look like the resolution is firmly here to stay.
We're now happy to recommend a number of Ultra HD 4K TVs, all of which deliver the necessary picture performance for SD, HD and 4K content, without breaking the bank.
Streaming 4K video has arrived with content growing by the month; 4K broadcast plans are well and truly underway; and Ultra HD Blu-ray is very much here.
Sold? In that case, you might want to check our round-up of the best 4K TVs you can buy...