It's been a long time coming.
The first 4K TVs went on sale back in 2012 but it wasn't until 2016 that the first 4K Blu-ray players, from Samsung and Panasonic, went on sale - alongside, thankfully, an increasing number of 4K Blu-ray discs.
So what is Ultra HD Blu-ray, how can you get it, and how much does it all cost? Allow us to provide some answers...
What is the Ultra HD Blu-ray specification?
The new format supports a resolution of 3840 x 2160, as well as high dynamic range (HDR) and higher frame rates (up to 60 frames per second).
HDR pictures can be delivered in one of two ways: either using the BDA-developed “BD HDR” section of the new specification, or via compatible HDR formats such as Dolby Vision.
Video will be encoded under the High Efficiency Video Coding (HEVC) standard, and use 10-bit colour depth and the Rec. 2020 colour space.
As for the discs themselves, the spec allows for discs in three sizes: 50GB with 82 Mbit/s, 66GB with 108 Mbit/s, and 100GB with 128 Mbit/s.
MORE: What is HDR TV?
MORE: Best HDR TVs 2016
What about Ultra HD Blu-ray audio?
The UHD Blu-ray specification also includes object-based immersive sound, such as Dolby Atmos and DTS:X. Now some Blu-ray discs already support this - so it's not unique to UHD Blu-ray - but the feeling is next-gen audio soundtracks will be more prevalent on Ultra HD Blu-ray discs.
Certainly many of the first films to have been released on 4K disc include Dolby Atmos soundtracks, including the likes of Mad Max: Fury Road.
MORE: What is Dolby Atmos?
MORE: What is DTS:X?
What else does Ultra HD Blu-ray offer?
The new discs will also support an optional digital bridge feature, which will allow you to copy Ultra HD Blu-ray content to an external hard disk drive and to portable devices, such as smartphones and tablets.
The spec also mandates that all Ultra HD Blu-ray players will be able to play legacy Blu-ray discs. Want 3D? Sadly, that isn't featured in the Ultra HD Blu-ray spec. With LG and Samsung phasing out 3D support in their TVs, this is perhaps understandable.
More after the break
What Ultra HD Blu-ray players are on sale?
Samsung chose the IFA show in September 2015 to release the first Ultra HD Blu-ray player, beating the likes of Panasonic to the "world's first" title... though on closer inspection it was something of a shell rather than the finished article.
Another option is the Panasonic DMP-UB900, which is now on sale in the UK and Europe and costs £600. Officially announced at CES 2016, the UB900 is THX certified and will support 4K video on-demand services. It'll also happily accept hi-res audio files and is fully networked so content can be streamed from NAS drives and media servers.
If you want to spend a little less, the Panasonic DMP-UB700 costs £400. It doesn't have quite the same stellar picture quality as its flagship stablemate, but still offers a clean and detailed picture.
Oppo's first Ultra HD Blu-ray player, the UDP-203, is another option. With support for high-resolution audio files, it could be a good option for audiophiles. It costs £600.
Sony's first model will go on sale in the spring of 2017, but it's a high-end number aimed at the custom install market. There's no price yet on the Sony UBP-X1000ES, but we can't imagine it will be cheap.
Finally, Microsoft's new Xbox One S games console also features a UHD Blu-ray disc drive. It's the first games console to be compatible with 4K Blu-rays, and at around £300, is one of the cheapest way to get a taste of the format. Though be warned, it's not quite up to scratch with rival standalone players. (You can read our full review here.) And as for the PS4 Pro? Sony didn't even bother giving it the capability, leaving PlayStation gamers lumbered with a 10-year-old Blu-ray disc player instead. Pah.
What Ultra HD Blu-ray discs are on sale?
Ultra HD Blu-ray discs are now on sale worldwide and in the UK, and include titles from 20th Century Fox, Sony Pictures and Warner Bros.
4K discs on sale include The Amazing Spider-Man 2, Chappie, Batman vs Superman: Dawn of Justice, Fantastic Four, Maze Runner: Chapter II - The Scorch Trials, Kingsman - The Secret Service, The Maze Runner, X-Men: Days of Future Past, Life of Pi, Hitman: Agent 47 and Exodus - Gods and Kings, Independence Day, Creed, Ghostbusters, Pineapple Express, Deadpool and Mad Max: Fury Road.
Recent releases include The Martian and Grimsby. You can see the full list, as well as future releases, here.
Will Ultra HD Blu-ray players play existing Blu-rays?
Yes, Ultra HD Blu-ray players will be fully backwards-compatible with existing Blu-rays. Ultra HD Blu-ray discs won't play on old players and there's little chance of upgrades for existing BD players, though - so you will need a new 4K Blu-ray player to get involved.
What TV do you need for Ultra HD Blu-ray?
On the one hand, an Ultra HD Blu-ray player will work on pretty much any TV - but of course unless it's an 4K Ultra HD TV, you won't see the full resolution. If your TV doesn't have the HEVC codec, the player will downscale the disc's content accordingly.
Any 4K TV should deliver a 4K picture, but only TVs with the latest spec will be able to take full advantage of what Ultra HD Blu-rays can offer. Your TV will ideally need to support HDR, which is increasingly seen as one of the key factors for getting the best possible picture. So if you want to make sure you're seeing 4K Blu-ray at its best, then check it's HDR-compatible.
Look for a TV bearing the Ultra HD Premium logo - this means it will deliver 4K in all its glory.
Do you need a new AV receiver for Ultra HD Blu-ray?
Yes and no. If your system currently uses an AV receiver to do the HDMI switching, and carry the audio and video over HDMI around your system, then this won't work with 4K Blu-ray unless your AV receiver is 4K-compatible.
The good news is that most home cinema amplifers released in the last year or so are 4K compatible, such as the Award-winning Denon AVR-X2200W, for example. Look for HDCP 2.2 and HDMI 2.0a in the specifications for a clear indication of 4K compatibility.
If your AV receiver isn't 4K-compatible, then you will need to run a separate HDMI cable from your Ultra HD Blu-ray player to your screen for 4K video, as well as one from the player to your amplifier for audio - this is why the new 4K Blu-ray players have two HDMI outputs.
MORE: Best AV receivers 2016
Is Ultra HD Blu-ray worth it?
The industry certainly thinks so, but then of course they're eager to see consumers shell out on new equipment and discs. Victor Matsuda, chairman, BDA promotions committee, said: "For years, Blu-ray Disc has set the standard for high-definition picture and audio quality in the home. Ultra HD Blu-ray will do the same for UHD home entertainment."
While Ron Martin, VP of Panasonic's Hollywood Lab and a crucial player in the development of Ultra HD Blu-ray, told What Hi-Fi? that 4K discs would beat 4K streaming: "[A disc format] is the only repeatable, reliable way to do it. Streaming has certain advantages but many disadvantages."
The good news? We agree. Read our comparison review to find out why we think 4K Blu-ray beats 4K streaming...4K Ultra HD TV reviews