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HDMI 2.1: What you need to know

A new version of HDMI is coming soon, and there are some big changes -- including support for resolutions up to 10K as well as a new cable. 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. HDMI (High Definition Multimedia Interface) is the main audio/video connection for TVs, Blu-ray players, game consoles, video streamers, sound bars, computers and more. It carries both video and audio in one cable, allows digital encryption, and generally delivers perfect video and audio quality without any degradation.

Today's devices mostly use HDMI version 2.0, but in 2018, many will likely transition to version 2.1. How does that affect you? Not much. You can't upgrade your current TV to 2.1 spec, but in reality, you won't need to. This update is quite forward-thinking and takes into account formats and resolutions that won't be widely available for years.

Sarah Tew/CNET

A TV bought in 2018 could very well have HDMI 2.1, but even it won't take full advantage of the connection's potential. And a TV bought today will be able to display video to its own full potential using HDMI 2.0. In other words, lack of HDMI 2.1 is no reason to put off buying a new TV.

So while HDMI 2.1 is all about the future, it's still worth learning about today -- if only to warn you against buying overpriced HDMI cables labeled as "2.1." Here's a look at what the new spec is, and more importantly, what it isn't.

The short version

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

  • The physical connectors and cables look the same as today's.
  • Improved bandwidth from 18Gbps (HDMI 2.0) to 48Gbps (HDMI 2.1).
  • Can carry resolutions up to 10K, frame rates up to 120fps.
  • New cables required for higher resolutions and/or frame rates.
  • Spec is still being finalized, expected to publish April-June 2017.
  • First products could arrive late 2017, but many more will ship in 2018.

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

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. So down the road we're likely going to see higher frame rate TVs, and eventually, higher resolutions (8K, and so on).

This is 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 120fps material, or their 8K TVs 60fps material. Far future versions of ourselves.

Unless you're a gamer, these high frame rates are superfluous. There's no source other than a PC that can output more than 60fps, and there's basically no content (yes, a few HFR movies, but they're very rare).

The higher resolutions are pretty optimistic too, since no company has announced an 8K TV for sale. Even if they did, it'd be years before we'd see widely available content. There's barely enough 4K content for most people right now, so 8K is still a long way off.

Useful additions

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.

Here's where we mention that Dolby Vision HDR already uses dynamic metadata, which can pass over a existing HDMI connections. At CES 2017, Blu-ray players with Dolby Vision were announced by LG and others and will start shipping early this year. They should work fine with current Dolby Vision-equipped TVs.

hdmi-hdr3imagecomparison.jpg

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, 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-compatitble sound bar, your current High-Speed cables should be able to transmit eARC.

hdmi-gamemodevrr.jpg
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. 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 a 48G 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. The "48G" cables will have 48Ghz bandwidth, roughly 2.6 times what the 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).

hdmi-bandwidthcomparison.jpg

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

HDMI Forum

There's no reason to buy a 48G cable now. The first generation of these cables will be overpriced and do not do anything 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.

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 a 48G cable.

On the color front, it 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?

The HDMI Forum, which is in charge of the HDMI spec, plans on releasing the complete specification in Q2 (so, between April and June). This is likely too late to implement on any 2017 televisions, not that they need it. We might see a few scattered products with 2.1 this year, and a lot more next year.

With the non-bandwidth related updates (Dynamic HDR, eARC), it is possible that a firmware update might give your TV those capabilities. The HDMI Forum has passed the buck back to the manufacturers, saying it "depends on manufacturer implementation." So if you have a TV with HDMI 2.0 or 2.0a, keep it updated.

So to sum up, this is a big update to the HDMI connection, but it's unlikely to affect you much right now. It's 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.


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.