HDMI 2.1: Why It Matters for PCs and TVs in 2021

We all know good old HDMI. For quite some time, it has been the typical cable you use to connect a laptop, a game console, or a cable or satellite box to a TV.

Nowadays, though, our old buddy can do much more than that, especially once you factor in the HDMI 2.1 specification. This latest HDMI spec has been bandied around for a couple of years now (hit the link for our earlier primer on it), but the latest consumer electronics are only now starting to support the new standard. And 2.1 brings with it some exciting "today" improvements—plus some future-looking potential—over existing HDMI specifications.

Major devices that support it include the big two new gaming consoles (the Microsoft Xbox Series X and the Sony PlayStation 5), leading-edge gaming graphics cards (including the Nvidia GeForce RTX 3080 and the AMD Radeon RX 6800XT), and a wide range of TVs. That said, HDMI 2.1 isn't a front-line feature that gets advertised, or explained, with most PC and consumer-electronics gear. Indeed, you may not see the term at all in a store or when shopping online, even when looking at gear or cabling that supports it. (More about that in a bit.) Let's get into how HDMI 2.1 works, and help you decide whether your next big tech purchase should include it.

The Basics: HDMI Versus DisplayPort

Before we get into HDMI 2.1 specifics, let’s put the spotlight on DisplayPort, HDMI’s main rival for carrying a cutting-edge display signal these days. Both connections support the same goal of providing audio and video over a single cable, though each has its focus area. HDMI is the home entertainment go-to for TVs and game consoles, while DisplayPort is a more common choice for connecting to PC monitors (though HDMI can be used for that, too).

Often, PC-centric display devices will support both HDMI and DisplayPort (providing inputs for both), so the choice then comes down to which one works best for your specific usage case. (See our feature HDMI vs. DisplayPort: Which Should I Use for My PC Monitor? for some guidance on that.) However, based on HDMI 2.1’s improvements, it is a better choice for home entertainment needs for some reasons that may be new to you. It's also working up some steam on the PC and console-gaming side.

The Big 2.1: The Improvements From HDMI 2.0 to HDMI 2.1

The HDMI specification has gone through several revisions. HDMI 2.0, the immediate predecessor of HDMI 2.1, was announced in 2013, but it didn’t see widespread adoption until several years later, when 4K TVs finally began filtering into the mainstream. HDMI 2.0’s claim to fame over its last major HDMI-version predecessor, HDMI 1.4, was its support for "4K60"—that is, supporting 4K (3,840-by-2,160-pixel) video playback at a smooth 60 frames per second (fps). That frame-rate limit was 30fps with HDMI 1.4.

But that’s all—smoother video playback—that HDMI 2.0 truly brought to the table, versus prior HDMI versions. It was an important step, to be sure, but today’s media demands an even-higher-bandwidth solution for a more enjoyable and refined viewership experience.

Let’s dive into the features one by one. One key thing to know: HDMI 2.1 devices need to support only one of the following features to be advertised as an HDMI 2.1 device. That’s a potential concern for buyers who are depending on more than one of these new features, or on a specific one being present. (More on that later.)

Smoother, Higher-Resolution Video

HDMI 2.1 looks toward the future with its support for up to a 10K (10,240-by-4,320-pixel) native resolution. Now, no TVs or PC monitors support a resolution that high just yet. (And never mind the question: Where would you get 10K content?) HDMI 2.1’s more immediate benefit will be support for "4K120," which is 4K video at up to 120fps.

Near-term, this could be a boon for a subset of demanding PC and console gamers. These days, among serious players, 60fps is the more-or-less accepted minimum for smoothness in competitive gaming. But 120fps looks far smoother, and that threshold will have great appeal for competitive esports players and sticklers for gaming visual quality. Acer, for one, demonstrated 4K Predator and Nitro monitor models at CES 2021 that can do this kind of high-refresh-rate 4K play over an HDMI 2.1 connection. So did Asus.

Also, those frame rates' time has come. It's worth noting that with some games, the latest high-performance gaming PCs, based on up-to-the-moment AMD and Nvidia GPU silicon, can produce triple-digit frame rates at a 4K resolution. Until the past year, that was usually a challenge for all but the very best video cards. So even if the HDMI 2.1 interface had been widely deployed before now, the power to leverage it, in many cases, would have been scarce.

For home entertainment buffs, HDMI 2.1 also supports 8K (7,680-by-4,320-pixel) content at 60fps. Like 4K TVs increasingly came to dominate the TV field in the mid-2010s, 8K TVs will become more and more the norm as we head into the mid-2020s. That said, streaming video content even at 4K is relatively new. So it will likely be several years before 8K devices and, just as important, their supporting content become mainstream.

Dynamic HDR

High Dynamic Range (HDR) isn’t a new concept. It allows still-image or video content to appear noticeably brighter or darker by expanding the contrast range beyond its normal values. However, it is typically implemented as static HDR, where one setting works for all content (for example, an entire movie).

Dynamic HDR improves on this by allowing frame-by-frame tuning for a better visual experience. It allows each scene in a movie to use the full range of colors, contrast, and brightness. HDMI 2.0 partially supports it for 4K60 content, but HDMI 2.1’s increased bandwidth allows dynamic HDR with 4K120 and future HDR standards.

Enhanced Audio Return Channel (eARC)

This technology streamlines audio from a source, such as a cable or streaming box, through a TV to a destination audio/video receiver or speaker bar. This was possible prior to HDMI 2.1, but not through a single HDMI cable.

Put another way, you could have a streaming box connected to your TV via HDMI 2.1, then connect the TV to an A/V receiver or a sound bar with another HDMI cable. It’s a true passthrough to simplify a home theater setup with fewer cables.

Variable Refresh Rate (VRR)

A display’s refresh rate determines how often its picture will be redrawn. The standard for TVs and monitors is 60 hertz (Hz), which translates to 60fps. (See our feature TV Refresh Rates Explained: 60Hz, 120Hz, and Beyond.)

For gamers, however, a static refresh rate can be problematic. If a display is running at 60Hz, but the PC or game console is pushing out frames at anything other than exactly 60fps, the result can be an unwanted malady called "tearing," in which you see part of one frame and part of another at the same time, often misaligned. HDMI VRR eliminates this problem. The source will send a frame only when it has finished rendering it, instead of sending just a part of it, creating a smoother gaming experience.

PC gamers might sense a parallel between HDMI VRR and the existing Nvidia G-Sync and AMD FreeSync technologies, which serve a similar purpose. Like them, HDMI VRR is its own standard. All three technologies require both the source and the display or TV to support them.

Quick Frame Transport (QFT)

Another HDMI 2.1 benefit for gamers, QFT technology reduces, though doesn’t eliminate, what is called "input lag": the brief delay between your input on a control pad or keyboard and something happening in-game. QFT shortens the delay sending active video across the HDMI cable. This technology is just beginning to make an appearance in HDMI 2.1 devices.

Auto Low Latency Mode (ALLM)

Displays often include a gaming mode that turns off some features to achieve lower latency for more responsive gameplay. ALLM improves on this by allowing devices to automatically enable gaming mode. (Prior to HDMI 2.1, enabling gaming mode meant manually doing so through the display’s menu.) ALLM also disables gaming mode when it’s no longer needed. Think of it as a convenience feature.

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Quick Media Switching (QMS)

You know that black screen that appears briefly while switching between inputs on a TV, like going between your cable box and the Amazon Prime app on a streaming stick? That usually occurs if the refresh rate differs between video sources. QMS eliminates the black screen under that condition by clever use of VRR (explained above) to transition video seamlessly from one source to another. (Note that you’ll still get the black screen if the resolution differs between sources, however.)

How to Identify an HDMI 2.1 Device: It's Tricky

Devices that support HDMI 2.1 will likely say so in their product details, under their input/output connections. However, as mentioned up top, just because a device has an HDMI 2.1 port doesn’t mean that it supports all HDMI 2.1 features.

This is unfortunate, from a consumer-understanding perspective. A device can support just one of them and still be advertised as an HDMI 2.1 device. Therefore, it pays to check with the device vendor regarding which specific HDMI 2.1-relevant features are supported. (And remember, both your source and your display must support a given HDMI 2.1 feature for it to work.)

Intriguingly, it may be possible for device vendors to make HDMI 2.1 features available on HDMI 2.0 devices via firmware upgrades. This, however, is by no means a guarantee, and no firmware upgrade will give you all HDMI 2.1 features.

How to Identify an Ultra High Speed HDMI Cable

One gotcha with HDMI 2.1 is that it generally requires a new Category 3 cable, marketed as an "Ultra High Speed" HDMI cable, supporting 48Gbps of bandwidth. An HDMI 2.1 device can still work with an older Category 2 (18Gbps) cable, though it will not support all of HDMI 2.1 features, notably 4K120.

Be warned of some crucial jargon here with real-world consequences. Be careful not to confuse Ultra High Speed HDMI cables with Premium High Speed HDMI cables. The latter are Category 2 cables that went through HDMI’s optional certification program to guarantee support for 4K60. Ultra High Speed HDMI cables are also required to go through a certification program, and will always be marketed as an Ultra High Speed HDMI.

Note that an HDMI cable will never be advertised with an HDMI version number; HDMI’s licensing prohibits it. For HDMI 2.1 support, look for the "Ultra High Speed HDMI" name on the box. HDMI's licensing body also has an app you can use to verify that an Ultra High Speed cable is genuine; if you are shopping in-store, download it and scan the QR code on the box. The app is available in an Android version and an Apple iOS version. (Also check out our guide to understanding the nuances of HDMI cables.)

Should I Buy Into HDMI 2.1?

HDMI 2.1’s mainstream adoption is accelerating, but 2021 is the first year in which it will be genuinely relevant. Its importance will only increase as 8K TVs become mainstream, but many of its benefits can be realized now, especially by gamers connecting to cutting-edge PC monitors that will roll out as 2021 progresses. Home entertainment can also benefit from its smoother frame rates and dynamic HDR.

Just be mindful while shopping for HDMI 2.1 devices: Verify that they support the specific HDMI 2.1 features you want. That caveat covered, HDMI 2.1 is a worthy wish-list item for your next device, especially if you plan on using that gear into the mid-2020s...and beyond.