HDMI explained: What do all the numbers mean, and which cables are best?

Demystifying the AV world’s most complicated connection

Your ultimate guide to HDMI

Since HDMI sockets and cables first appeared in 2002, they've caused a lot of trouble. They’ve been responsible for generations of AV equipment going suddenly and unceremoniously out of date, not to mention untold numbers of cable breakages due to their flimsy attachments.

Different HDMI sockets on different devices have long bamboozled people by supporting different features. People trying to run long HDMI cables have sometimes found they get no picture. Also, the era of smart TVs and ever-increasing data demands placed on HDMI cables means they now come in three different grades that you actually need to have at least a rudimentary understanding of.

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Despite all these issues, though, HDMI connections have endured. Mostly because for all their issues, they’ve remained almost endlessly upgradable, keeping pace with not just the demands of the AV world but, as we’ll see, the world of the smart home, too.

It’s also true, of course, that HDMI cables were designed with the best of intentions: to provide a single-cable digital video and audio solution.

Nonetheless, it’s clear that plenty of HDMI nonsense has happened along the way. So here we attempt to pick through the HDMI myths to provide only the facts that you really need to know.

Why aren’t all HDMI connections the same?

HDMI ports deal in digital data. And since the demands placed on digital data change much faster than things did in the analogue age, HDMI connections and cables keep having to evolve too.

So quickly has HDMI had to adapt, in fact, that there a number of different generations of HDMI port are simultaneously playing a key part in today’s AV world. In fact, sometimes a single product can carry multiple generations of HDMI.

The main HDMI generations you need to concern yourself with if you’re thinking of buying a new AV product now are v1.4, v2.0, and the upcoming v2.1. We'll look at each in turn.

HDMI guide: Everything you wanted to know, but were too afraid to ask

HDMI V1.4

HDMI v1.4 was a big deal when it debuted in 2009 because it was the first HDMI platform with enough data bandwidth for 4K picture resolutions. It can, though, only shift enough data to support 4K at up to 30 frames a second. Similarly, while it supports high dynamic range playback, that support is restricted with 4K to 8-bit colour quality, rather than the 10-bit or 12-bit support offered by later HDMI versions.

Many devices (such as Sky Q boxes, the original PS4, most projectors and many relatively affordable TVs) still carry these relatively affordable ports.

HDMI v1.4 also introduced the HDMI Ethernet Channel (HEC). This allows two connected devices to share a wired Internet connection - potentially very handy for smart home installations.

HDMI V2.0

Often known as the UHD HDMI, v2.0 widens provides much more bandwidth, so that it can better handle 4K video. Its 18.0 gigabits per second throughput is enough to support 4K at frame rates of up to 60Hz, as well as high dynamic range video up to the wide ‘Rec 2020’ colour space with 10/12-bits of colour resolution.

Also introduced with HDMI 2.0 is support for up to 32 audio channels at a high 1536kHz sampling frequency, and as many as four simultaneous audio streams and two simultaneous video streams.

HDMI 2.0b additionally added playback of the new Hybrid Log Gamma format already used by the BBC and expected to be taken up by other broadcasters soon.

HDMI 2.1 is the newest HDMI format, only formally launched on November 28 2017 - too late, it seems, to get onto any mainstream consumer electronics device to date. It should become widely available in 2019, though.

This really is a substantial update. For starters, it supports video resolutions up to 10K, paving the way for the next generation of 8K-resolution TVs. It also supports so-called Dynamic HDR, where extra scene by scene information is provided to displays to help them show their HDR pictures better. High frame rates up to 120Hz will be possible with any resolution, too.

HDMI 2.1 introduces some key gaming features, such as variable refresh rate support to tackle image lag, stuttering and frame tearing; quick frame transport to help screens display images faster; and a feature that can trigger displays to automatically switch into their fast-response game modes when a game is detected.

HDMI 2.1 also improves the HDMI Audio Return Channel feature described later in this article.

HDMI Overlap

There can be some feature fluidity between HDMI generations. For instance, the Dolby Vision dynamic HDR system has actually worked on every HDMI since v1.4. Also, Samsung has managed to get some HDMI 2.1 features (auto game mode, variable refresh rate support, support for other non-Dolby dynamic HDR formats) working on its current HDMI 2.0 TV connections.

Sky expects to be able to deliver HDR later this year, too, despite its Sky Q boxes only carrying HDMI 1.4 ports.

HDMI guide: Everything you wanted to know, but were too afraid to ask

HDMI and CEC

One potentially useful trick of HDMI cables for smart home applications is CEC. Short for Consumer Electronics Control, CEC lets you control multiple devices connected via HDMI using only one remote control. So, for instance, if you connect a CEC-enabled Blu-ray player to a CEC-enabled TV, you will get extra menu options that let you use your TV remote to control Blu-ray playback.

With the arrival of HDMI 2.0, CEC can potentially drive up to 15 devices via a single remote control.

CEC can currently be clunkily implemented or hard to follow on many devices, though - and many consumers don’t even know it exists. A concerted industry-wide push of CEC technology would likely help CEC realise its full smart home potential.

HDMI and ARC

HDMI connections have carried a handy feature called Audio Return Channel for a number of iterations now. This lets a single HDMI cable carry sound in two directions, so that, say, a TV can both receive sound from and send sound to an AV receiver, removing the need for a separate sound output cable from the TV.

This feature is enhanced with HDMI 2.1 to support the highest quality Dolby Atmos and DTS:X sound formats.

HDMI cables: What you need to know

There are now three different ‘standards’ of HDMI cable to be aware of.

Basic ‘category 1’ HDMI cables are not designed to carry the 18Gbps data rates associated with today’s HDMI 2.0 4K/HDR connectivity. As a result, while they can cost mere pennies, they’re probably best avoided now if you have any interest in 4K/HDR picture quality, or HDMI’s latest CEC ‘smart home’ capabilities.

Category 2 HDMI cables - also known as High Speed HDMI cables - are designed to handle the 18Gbps required to unlock HDMI v2.0 features. Category 2/High Speed cables should be labelled as such on retail websites.

The newest HDMI 2.1 format depends on data rates far higher than HDMI 2.0’s 18Gbps. In fact, it needs as much as 48Gbps. As a result, we’re already seeing Ultra High Speed HDMI cables capable of handling such huge amounts of data.

Good Category 2 HDMI cables may well handle most of HDMI 2.1’s requirements, but if you’re attracted by all the HDMI 2.1 benefits discussed either, it’s probably worth spending a little more on an Ultra High Speed design.

HDMI guide: Everything you wanted to know, but were too afraid to ask

Should you get Premium Certified HDMI cables?

The ‘Premium Certified’ badge for HDMI cables was created by the HDMI Licensing Group to show that a cable has passed the organisation’s internal 18Gbps tests.

While I guess it’s nice to see this reassurance, category 2 cables that haven’t paid for the Premium Certification should still handle HDMI 2.0’s demands perfectly well. And they’ll often be cheaper, too.

What are Active HDMI cables?

Most HDMI cables are passive, and can pass their signals in either direction. Active HDMI cables, though, only send their signals in one direction. Why? Because they contain power boosters that amplify the signal coming from your source as they send it on its way.

For most HDMI cable runs an active HDMI cable won’t be necessary. However, if you need to use a really long cable run (likely 30 feet or more), an Active HDMI cable may make the difference between a data-intensive signal making it or not, as HDMI cables generally become less reliable the longer they are.

Active HDMI cables are potentially more likely to be useful for smart home applications based on CEC technology than typical video set ups.

Are expensive HDMI cables worth it?

You can spend thousands of pounds even on quite short HDMI cables. But there’s absolutely no reason to. Unlike analogue cables, where higher quality ones can at least in theory deliver superior audio or picture results, HDMI’s digital nature essentially means that cables either carry enough zeroes and ones from end to the other to deliver a signal, or they don’t.

Some relatively expensive cables can offer handy tricks such as extra-strong mounts, or smart home-friendly flat cable profiles for running under carpets. Also, if you’ve got a very long cable run and a 4K or even 8K screen to feed, it is possible that a relatively expensive cable will carry all that signal bandwidth more successfully.

Even in these sorts of relatively unusual setups, though, there’s still no need to spend thousands or even hundreds of pounds on an HDMI cable.

The 5 best HDMI cables to buy

HDMI guide: Everything you wanted to know, but were too afraid to ask

Belkin Ultra High Speed HDMI Cable (2m)

$29.99, belkin.com | Amazon

Belkin's cable supports 4K, Dolby Vision, and can handle HDMI 2.1 48Gbps data flows. It's one of the more costly of the list, but easily one of the best.

HDMI guide: Everything you wanted to know, but were too afraid to ask

AmazonBasics High Speed 2.0 cable (1.8m)

$6.99, Amazon

The ultimate proof that you don’t need to spend much money at all to get even a decent ‘category 2’ high speed HDMI cable.

HDMI guide: Everything you wanted to know, but were too afraid to ask

QualGear High Speed Long HDMI 2.0 Cable (50ft/15.24m)

$39, qualgear.com | Amazon

This active category 2 cable is again proof that you don’t have to spend a fortune to get a reliable cable even for long cable runs. This cable is available in much longer versions, too, without the price ever becoming painful.

HDMI guide: Everything you wanted to know, but were too afraid to ask

Monoprice Certified Premium High Speed HDMI Cable (25ft)

$19.99, Monoprice | Amazon

If you want a fairly long running cable with the extra peace of mind of Premium Certification, this is an impressively affordable option.

HDMI guide: Everything you wanted to know, but were too afraid to ask

Ugreen high speed 270-degree angle plug (3m/10ft)

$10.99, Amazon

A great example of some of the installation innovations available in the HDMI cabling world. As well as using a flat cable arrangement, this Ugreen cable features a ‘right angle’ connection for close to wall installations.

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