From our experience, Ultra HD can look incredible, delivering impressive detail and clarity. But when it comes to 4K video content, for a long time we struggled to find much more than promotional videos of flowers and cityscapes. That's certainly started to change...
Video-on-demand streaming services such as YouTube, Netflix and Amazon Instant Video all offer films and TV shows, some free, some paid-for. But the biggest news is that Ultra HD Blu-ray discs and players are here.
While the players were promised before the end of 2015, we had to wait until March 2016 to see the Panasonic DMP-UB900 in our test rooms. Since then, we've looked at and loved the Oppo UDP-203 and, most recently, Sony's first effort in the UBP-X800.
Even Microsoft's latest Xbox One S console has an Ultra HD Blu-ray player built in. Like buses, you wait ages for one to turn up, and then...
We're also seeing more Ultra HD Blu-ray discs going on sale in the UK - and not only the latest releases.
As for 4K broadcasts, BT was the first out of the blocks with its BT Sport Ultra HD channel, but Sky now has a growing amount of 4K content on Sky Q. As well as sports such as Premier League football, cricket and the 2017 Formula One season, 4K coverage includes films such as Spectre and The Revenant, natural history programmes and documentaries, dramas such as Jamestown and comedies such as The Trip to Spain.
We round up the different ways you can watch 4K content right now...
How to watch 4K video on Netflix
Netflix was one of the first video-on-demand services to announce it would be supporting 4K streaming, and in April 2014, went live in the UK. But to access the content, you need to have the right kit.
To watch Netflix 4K online, your 4K TV will need to support the HEVC (High Efficiency Video Coding)/H.265 compression standard. The first generation of 4K TVs didn't support this, instead coming with the H.264 codec, which doesn't support most of the 4K content now available.
You'll also need to make sure your 4K TV (or other necessary kit) has an HDMI 2.0 connection that is HDCP 2.2 compliant. This ensures copy protection compliance for 4K content coming from an external source.
If you have a non-compatible 4K TV all is not lost, manufacturers can release software updates. Panasonic, for example, has released a software update for its AX802 series (you can read the What Hi-Fi? review of the 58in version) that means it can stream Netflix in 4K.
Alternatively, you can connect a separate box, such as the Amazon Fire TV (2015), to your TV and stream Netflix, as well as Amazon Instant Video in 4K.
The simplest way to see if your set is compatible is to check it against this full list of Netflix 4K compatible TVs.
You will also need to sign up to Netflix's 4K Ultra HD plan, which costs £9 per month. This subscription plan comes with the added benefit of the user(s) being able to watch content on up to four screens at any one time, all from the one account.
And finally, you need a solid internet connection. Netflix recommends a speed of at least 25Mbps, but ideally higher, for streaming 4K video.
Once you've ticked all those boxes, you're ready to start watching. But what content is out there? It's low on 4K movies but high(er) on 4K TV shows.
At first Netflix had only a few TV shows and some scenic footage to show in 4K, but the amount of content on offer has grown to 47 TV series, including The Crown, Stranger Things, House of Cards, Breaking Bad, 13 Reasons Why and Daredevil. There are also 22 documentaries, 13 movies and 14 standup comedy specials available at the time of writing. You can find a full list of live 4K content on Netflix here.
How to watch 4K on Amazon
Amazon is also offering 4K content through its Prime Video streaming service. For those with Prime memberships, a range of Amazon Original TV shows are available at no extra cost.
You can watch 4K video through the Amazon Prime Video app on compatible TVs and the latest 4K Fire TV box. You can see a full list of Amazon Prime Video devices here - note this is a list of devices that are compatible with the movie streaming app as a whole and not necessarily 4K content.
The Amazon 4K service was initially available only on Sony 4K TVs, but the latest models from most of the major manufacturers now come with the app pre-installed. If you have an older set you may need to perform a software update.
Microsoft recently updated the Amazon Prime app for its Xbox One S games console, so it now supports streamed 4K HDR content.
Amazon's service offers a good selection of 4K films and TV shows. You'll find TV shows, including Amazon Originals such as The Man in the High Castle, The Grand Tour, Alpha House Season 2, Mad Dogs, Transparent and Red Oaks, all available in 4K and all included in the Prime price. Mozart in the Jungle, The Grand Tour and Red Oaks are also available to stream with High Dynamic Range (HDR).
Films available to stream include The Amazing Spider-Man 2, Moneyball and The Da Vinci Code - all on a pay-as-you-go basis. Rental prices start at £1, though £7 is more standard (not all films can be rented). To buy, you're looking at between £5 and £14.
How to watch 4K on YouTube
YouTube has been supporting 4K Ultra HD video since 2010, but, as with the two previous services, there are requirements.
YouTube Ultra HD videos don't use H.265 compression. Instead, they use the VP9 codec, which is royalty-free, meaning its adoption rate could potentially be higher. It is also said to be more efficient when it comes to streaming Ultra HD video.
So how do you watch 4K YouTube videos online? Google implemented the VP9 codec into its Chrome browser and YouTube in 2013, so both have been able to support 4K streams for some time. If you search 4K content within YouTube right now, you'll be able to select 4K as a quality option on each video.
But, as with HEVC/H.265, VP9 needs compatible hardware (ie. a 4K screen) to watch it on. Most new PCs should support the VP9 codec, but it's something to keep an eye out for.
If you don't have a compatible display, the video will be downsampled to the maximum output of your monitor.
More after the break
Where else can you stream 4K video?
UltraFlix is a 4K streaming network from NanoTech, and has apps on Samsung, Sony, Vizio, Sharp and Hisense TVs. The 4K UltraFlix Network App claims to offer the "world's largest library of 4K VOD content", including "hours of free content" from movies, concerts, documentaries and special events to 40 made-for-IMAX theatrical titles.
We accessed the app through a 2016 Sony TV, but prices for content are in US dollars. We watched some free content but noticed it buffered quite a bit, even with an 18Mbps Internet connection.
What about watching 4K TV broadcasts?
BT became the first broadcaster to bring an Ultra HD channel to the UK, with the launch of BT Sport Ultra HD. The channel launched in August 2015 and promised to show one live Ultra HD event per week.
The focus is primarily on football, but it has also shown other events including the MotoGP, NBA basketball and Aviva Premiership rugby.
The channel is supported by the majority of 4K TVs released in 2014/15, but you will need to subscribe to the Ultra HD package at £18 per month, have an Infinity Fibre broadband connection and get the new BT Ultra HD box fitted.
Sky claimed it would offer the "UK's most comprehensive Ultra High Definition service" through its Sky Q platform in summer 2016, and it certainly stuck to that promise. Sky Q Ultra HD launched in August 2016, with a wide range of content available at no extra cost to Sky Q subscribers (provided you subscribe to the relevant TV package).
While football again features heavily, there's also a load of movies, dramas and natural history programmes as well. Sky also confirmed the 2017 F1 season will be broadcast in 4K, as will this summer's Test cricket.
You'll need a Sky Q 2TB box (known as the Sky Q Silver box when it launched), as well as a subscription to Sky Q Multiscreen. For those new to Sky, this starts at £32 per month, but doesn't include a subscription to Sky Sports or Sky Cinema.
While it is a huge step forward for 4K broadcasts, Sky's content won't come with the added benefit of High Dynamic Range (HDR). "HDR as a standard hasn't settled down yet," says Sky's director of TV experience David Cameron. "When it does, we'll look at moving forward."
The Sky Q 2TB box also upscales standard and high definition content to 2160p, 4K resolution.
What about 4K on terrestrial TV? The BBC filmed Planet Earth II in 4K and released a four-minute 4K clip via iPlayer, but is still keeping quiet on when it'll actually broadcast in the resolution. At the moment, it looks set to continue with its "internet first" approach.
New specifications were recently added to the UHD standard, with UHD broadcasts supposedly ready to start in 2017. But don't hold your breath. Not so long ago, the BBC claimed it would aim to broadcast 4K as standard by 2016 - and look how that turned out.
What about 4K on PlayStation or Xbox?
Sony has launched its own 4K Video On Demand service in the form of Video Unlimited 4K, which sat alongside its Music Unlimited and Video Unlimited services. The service has since been rebranded as PlayStation Video.
The service includes 4K content, but only in the US. To access 4K content, you need one of Sony's 4K Media Players, such as the FMP-X1, or one of the selected US Sony 4K TVs. Films range from $8 for a 24-hour rental to $30 to buy. Sony says it has "no plans" to bring the 4K Media Player to the UK.
Sony's PS4 Pro is equipped for playing 4K games, but it doesn't have an Ultra HD Blu-ray drive. Microsoft's Xbox One S does, however, but it's not the best disc-spinner around. In our test, we found picture quality to be somewhat lacking.
Sony has also launched an Ultra app, which brings 4K videos to selected Sony Android 4K TVs. Again, it's only available in the US for now.
Xbox One S owners in the US can now stream 4K HDR films through Microsoft's Films & TV service. The first title made available for streaming is The Lego Batman Movie, which costs $30, around the same price as the 4K Ultra HD Blu-ray version of the same film.
Whether more movies will be released or the service will make its way to the UK remains to be seen.
How to watch 4K Blu-ray
For many, getting a broadband connection that's fast enough to support 4K streaming (realistically 15Mbps at the very least) isn't possible right now. Therefore a better way to get 4K content into the home would be on a disc format.
The good news is Ultra HD Blu-ray is here. Discs that can handle resolutions up to 3840 x 2160 and up to 60fps (frames per second) can be classed as Ultra HD and the format also supports high dynamic range (HDR), higher frame rates (up to 60fps) and object-based immersive sound, such as Dolby Atmos and DTS:X.
HDR on 4K Blu-ray discs appears in two flavours: HDR10 and Dolby Vision. Video is encoded under the High Efficiency Video Coding (HEVC) standard, and uses 10-bit colour depth and the Rec. 2020 colour space.
Not convinced that UHD Blu-rays are the future? There's a strong argument that they're superior to 4K streaming... and how else are you supposed to watch Planet Earth II in eye-poppingly sharp resolution?
Make your own 4K video
Still not satisfied? You could always create your own 4K Ultra HD content.
An increasing number of phones are now able to record 4K video, including the iPhone 7 and 7 Plus and Samsung's Galaxy S8+, meaning you can make your own 4K movies in no time. And of course there are also plenty of 4K cameras available.
It's one easy and cost-effective way to fill the 4K gap. Though we're guessing your masterpieces may not match the quality of House of Cards...
The 4K verdict
The growth of 4K content means the format is finally becoming a tempting proposition.
The amount of content available to stream is increasing all the time, and while it relies on a high-speed internet connection, it offers the most extensive catalogue.
4K Blu-ray discs are here too, and from what we've seen they offer a superior performance to streaming. Rest assured, the trickle of available titles will soon become a flood.
As for 4K TV broadcasts, things are starting to move in the right direction. Now that Sky and BT are broadcasting in the format, interest is bound to catch on. The main obstacle is the cost. 4K TVs are becoming more affordable, but Sky and BT's services aren't cheap.
On the bright side, it's now more viable than ever to put a 4K TV in your home. And there's finally something to watch on it.
Have we missed a 4K source off our list? Let us know in the comments below...