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HDMI 2.1: What you need to know

A new version of HDMI is coming, and there are some big changes -- including support for resolutions up to 10K as well as a new cable. However, don't worry about it yet. Here's the skinny on fatter AV bandwidth.

HDMI Forum, Phoenix Productions

OK, let's get this done up front. Yes, there's a new cable with HDMI 2.1, but you don't need to upgrade. At least not yet.

HDMI 2.1 brings new features and a lot more bandwidth to the venerable cable and connection. However, it's going to be many years before you'll see it on the average television. In fact, we don't expect it to be in any of the TVs announced at CES 2019, although some TV makers might claim otherwise.

The connector itself isn't changing, so your current cables will work even when you finally get a device with HDMI 2.1. You will need new cables to take advantage of the new features and resolutions possible with 2.1 but again, it will be years before those become commonplace.

Today's devices mostly use HDMI version 2.0, or one of its several iterations. It's possible well see a handful of TVs in 2019 with full or partial 2.1 implementations. How does that affect you? Not much. You can't upgrade your current TV to 2.1 spec, and there are no HDMI 2.1 sources yet. This update is quite forward-thinking and takes into account formats and resolutions that won't be widely available for years. However, if you're considering certain new TVs in 2018 and 2019, you should make sure you understand the limitations of 2.0, and what 2.1 will offer if you choose to wait on your TV purchase.

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Sarah Tew/CNET

The short version

Don't like reading (much)? Allow me to fire some HDMI 2.1 bullets.

  • The physical connectors and cables the same as today's HDMI.
  • Improved bandwidth from 18 Gbps (HDMI 2.0) to 48 Gbps (HDMI 2.1).
  • Can carry resolutions up to 10K, frame rates up to 120fps.
  • New cables required for higher resolutions and/or frame rates.
  • The first products were due in 2018, perhaps some will arrive in 2019.

Want more words about the numbers behind the acronym? Read on.

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All about the bandwidth

When you increase the resolution of a TV signal, the amount of data of that signal goes up. A 3,820x2,160 4K UltraHD signal over HDMI is roughly 4 times the amount of data as an HD 1,920x1,080 signal. If you think of cables as pipes, you need a bigger pipe to transmit a 4K signal than a 1080p one. The same is true if you increase the frame rate. You need a bigger pipe to transmit a 60 frame-per-second image than you do a 24fps image of the same resolution.

Though most current HDMI cables can handle nearly all of today's content, the TV industry never sits still. Down the road we might see higher frame rate TVs, and we're already starting to see higher resolutions, like 8K TVs. Don't worry, they're not going to be common any time soon either. Even way farther down the road, maybe we'll even see 10K TVs.

This is predominantly what HDMI 2.1 is for. Not for 99 percent of people now, but for the future versions of ourselves who want to send their 4K TVs native 120fps material, or their 8K TVs 60fps material. Far future versions of ourselves playing content that doesn't currently exist...

Unless you're a gamer. Personal computers, and high-end gaming rigs at that, are the only current source that can output more than 60fps. Otherwise there's basically no content outside of a couple of HFR movies. Since there's no indication of movies or TV moving towards higher framerates, except for perhaps sports, the higher framerates possible with the HDMI 2.1 specification are likely to go unused by most consumers. Yes, in theory you could finally send your 120 Hz TV a 120 Hz signal (which isn't how they work now), but again, there's no 120 Hz content now or planned, so this is pretty unlikely.

Already we're seeing 8K TVs, however, with the 85-inch Samsung Q900 in the US, and several models elsewhere in the world. Since even 4K is higher resolution than most people need, given their TV size and seating distance, this too is overkill. However, TV manufacturers love increasing resolution because it's relatively easy to improve, and makes for an easy marketing push as "better." It's inevitable we'll have 8K TVs, but that's many years away, and those TVs will be better and cheaper than today's models.

So if you're considering buying an 8K TV now there's something important to keep in mind: These TVs aren't HDMI 2.1. Not fully. So when inevitably we get 8K sources that have HDMI 2.1 outputs, these first-generation TVs might not be compatible. This is exactly what we saw with early 4K TVs, none of which are able to play content from 4K Blu-ray players or 4K media streamers. 

Useful additions

While the new resolutions and frame rates get all the headline buzz, but there are some other improvements that will be more useful for most people.

"Dynamic HDR" is an amusing name for a big improvement. High dynamic range is our favorite picture-quality improvement since high-definition itself, and right now the most common HDR format is HDR10. It uses something called metadata to tell the TV how to treat a piece of HDR content. In the current version of HDR10, that metadata is applied once and once only, on a per-program basis. As in, you get One Set of Data to Rule Them All.

Dynamic HDR can vary how each scene or even each frame looks, not just the program as a whole, to better suit that scene (or frame). Here's a video that shows some examples (but remember, you're viewing it on non-HDR screens). Basically, a dark scene with bright highlights (campfire at night) would take advantage of HDR differently than a bright scene with dark areas (someone under a pier on a beach at noon). If these scenes were in one movie, static HDR would treat these the same, while Dynamic HDR would let each scene look its best. HDMI 2.1 enables Dynamic HDR, but it also needs to be present in the content to work. 

Dolby Vision, HDR10+, and certain flavors of Technicolor's Advanced HDR, already uses dynamic metadata and can pass over a existing HDMI connections. This aspect of HDMI 2.1 ensures going forward this will be possible without a proprietary format (HDR10 has no licencing fees). It may be a while before we see how this is implemented, however, if at all.

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Remember, you're viewing an SDR image on an SDR display, so this is for illustration purposes only. The idea of Dynamic HDR is for each scene to be able to take advantage of HDR to look its best. Current Static HDR can only have one set "look" for the entire movie or show.

HDMI Forum

"eARC" is the next evolution of Audio Return Channel, which allows simpler connections between AV devices like TVs, video players and sound systems. eARC has support for "the most advanced audio formats such as object-based audio, and enables advanced audio signal control capabilities including device auto-detect."

Basically this means Dolby Atmos over ARC at full resolution, which you currently can't do. However, your current cables probably can. If, in the future, you buy an HDMI 2.1-compatible TV and an HDMI 2.1-compatible sound bar, your current High-Speed cables should be able to transmit eARC. Audio doesn't require the bandwidth that video does.

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HDMI Forum

"Game Mode VRR" is a potentially interesting feature for gamers. It allows for "variable refresh rate, which enables a 3D graphics processor to display the image at the moment it is rendered for more fluid and better detailed gameplay, and for reducing or eliminating lag, stutter and frame tearing." In other words, there will be less of a buffer for frames while the video card creates the image so you won't have to choose between image artifacts and input lag, ideally reducing both. If this sounds familiar, it's because it's similar to Nvidia's G-Sync and AMD's FreeSync, both only available over DisplayPort. We wrote more about this feature in How HDMI 2.1 makes big-screen 4K PC gaming even more awesome.

Game Mode VRR will also work over current cables (between two pieces of 2.1-compatible gear), though if you're trying to push greater-than-4K60 video, you'll need an Ultra High Speed HDMI cable. 

Speaking of that...

New cable

For the first time in a while, there is a new cable. It looks... well, it looks the same as the old cable. There's no new connector; that stays the same. These were originally called "48G" cables since they will have 48 Gbps bandwidth, though now they're officially called Ultra High Speed HDMI cables. These have roughly 2.6 times the 18 Gbps better-made HDMI cables have now. These cables are backward compatible, so they'll work with all your other HDMI gear (at whatever speed that gear operates).

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A visual representation of how much more bandwidth the upcoming 48G cables can handle. 18 Gbps is plenty for nearly all current content.

HDMI Forum

There's no reason to buy an Ultra High Speed HDMI cables cable now. The first generation of these cables are rare, overpriced, and do nothing for your current gear. When, down the road, you have gear that can take advantage of the extra bandwidth or features, then you should upgrade. They'll be cheaper then, too. Check out What HDMI cable do you need? for some cheap options now.

Raw specs

The increased resolution and frame rate possibilities are a futurist's dream:

  • 4K50/60
  • 4K100/120
  • 5K50/60
  • 5K100/120
  • 8K50/60
  • 8K100/120
  • 10K50/60
  • 10K100/120

You should be able to get 4K/60 with current cables, but the rest will need an Ultra High Speed HDMI cable.

On the color front, 2.1 supports BT.2020 and 16 bits per color. This is the same as HDMI 2.0a/b, and is what makes wide color gamut possible.

When?

We had expected, based on information we've gotten in the nearly 2 years since 2.1 was announced, to have seen TVs with 2.1 already. At this point it's unclear if even 2019 models will have full 2.1 implementation. Probably not. 

We will likely see partial implementation. Which is to say, some of the features or abilities of HDMI 2.1, but not all. So perhaps a TV with 8K/30 input capability, but not 8K/60 or 120. This is what the 8K Samsung can do. The non-bandwidth related updates are likely as well, like eARC or Variable Refresh Rate, the latter already seen on the Xbox One X. It will be important to keep track what a TV can do, and what it can't. Some companies may start marketing a TV as "HDMI 2.1" but only really have one or two of these features, not full HDMI 2.1.

So at this point buying any 8K TV is risky, since it's impossible to say for sure what missing features might be added to make it compatible with all that 2.1 offers. It's possible that a firmware update might give your TV those capabilities if it doesn't out of the box, but then, it might not. TV manufacturers are very hit-or-miss when it comes to adding features to older televisions. Sometimes it's not physically possible, other times it's not economically possible. 

HDMI 2.1 is like a brand new 10-lane highway in the middle of the countryside. There's not much reason for it right now, but it offers an easy way to expand in the future. If you're not considering an 8K TV then it's a 10-lane highway in the countryside of a different state or country. Cool, but not something that will impact your immediate future.


Got a question for Geoff? First, check out all the other articles he's written on topics such as why all HDMI cables are the same, LED LCD vs. OLED, why 4K TVs aren't worth it and more. Still have a question? Tweet at him @TechWriterGeoff then check out his travel photography on Instagram. He also thinks you should check out his sci-fi novel and its sequel.