HDMI 2.1: Những điều bạn cần biết

Even though the cable looks the same, modern HDMI connections are vastly more capable than when they first arrived over 20 years ago. The latest version, called 2.1b, is only a small update, but 2.1 in general is a big deal with lots of performance improvements and new features. The standard is found in the best new TVs, including recent models from LG, Samsung, Sony, TCL, Vizio and more. HDMI 2.1 is also on both of the next-generation game consoles, the PlayStation 5 and Xbox Series X. In fact, to get the most out of those
consoles
 you’ll want a TV that supports at least some HDMI 2.1 features.

That doesn’t mean you need HDMI 2.1, however. For most people the extra features are not a good enough reason to buy a higher-end TV. If you’re on a budget, those new consoles will play perfectly well (and still look spectacular) on a TV that lacks HDMI 2.1. Many midrange and higher-end sets support the new connectivity standard, though, so it’s worthwhile to understand what it means if you are looking to purchase soon.

The short version is HDMI 2.1 allows for higher resolutions, higher frame rates and a lot more bandwidth. The connector itself isn’t changing, however, so new HDMI 2.1 gear will be backward-compatible with your current cables and equipment. But if you want to take advantage of everything 2.1 has to offer, you’ll need some select upgrades and potentially new cables, too. Here’s what you need to know.

Read more: Best HDMI cables for your new 4K and HDR TV

The really short version

Don’t like reading (much)? Here are the highlights:

• The physical connectors and cables look the same as today’s HDMI.
• Improved bandwidth from 18 gigabits per second (HDMI 2.0) to 48Gbps (HDMI 2.1).
• Can carry resolutions up to 10K, frame rates up to 120 frames per second.
• New cables are required for higher resolutions and/or frame rates.
• Many new TVs have at least one HDMI 2.1 input.
• The main sources that can take advantage of 2.1 right now are the PlayStation 5 and Xbox Series X, as well as high-end graphics cards.

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, and a basic 8K/30, with current cables, but the rest will need an Ultra High Speed HDMI cable. More on these new cables below.

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.

Those are just the highlights, though. Read on for the details.

All about the bandwidth

When you increase the resolution of a TV signal, the amount of data of that signal goes up. A 3,820×2,160-pixel 4K Ultra HD signal sent over HDMI is roughly four times the amount of data as an HD 1,920×1,080 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 60fps image versus, say, a 24fps image of the same resolution. More images per second means more data.

Though most current HDMI cables can handle nearly all of today’s content, the TV industry never sits still. We’re already seeing TVs that are capable of higher frame rates, plus higher resolution TVs, like those with 8K. Don’t worry, they’re not going to be common anytime soon. Even way further down the road, maybe we’ll see 10K TVs.

This is predominantly what HDMI 2.1 is for: higher resolutions and frame rates that aren’t necessary for most people right now.

Well, unless you’re a gamer. PCs and high-end
gaming
rigs, plus the PS5 and Xbox Series X, are the only sources currently that can output 4K at more than 60fps. While there are a handful of movies or TV shows with higher frame rates, you won’t find those versions on Netflix or Vudu. 

Though we are seeing a handful of 8K TVs, actual 8K content is almost nonexistent. This is largely because 8K sources are also basically nonexistent. Your average
Roku
or
Apple TV
can do 4K, and that’s it. 

So as far as the additional potential bandwidth of HDMI 2.1, when it comes to resolution and frame rates, only a few TVs can take any advantage of it, and then only with gaming consoles and PCs. There’s more to HDMI 2.1 than just bandwidth, however.

New features

While the new resolutions and frame rates get all the headline buzz, 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 may be viewing it on a non-HDR screen). 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 and HDR10+ already use dynamic metadata and can pass over existing HDMI connections. This aspect of HDMI 2.1 ensures this will be possible going forward without a proprietary format (HDR10 has no licensing fees). 

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.

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 which…

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 cables were originally called “48G” since they will have 48Gbps bandwidth, though now they’re officially called Ultra High Speed HDMI cables. These have roughly 2.6 times the 18Gbps bandwidth that 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).

You probably don’t need to buy Ultra High Speed HDMI cables right now. Even with 4K TVs nearly all your gear should work fine with your current cables. There are, however, important exceptions. The biggest is with the new gaming consoles, the PlayStation 5 and the Xbox Series X. These are capable of 4K resolutions at 120 frames per second. That’s almost certainly going to require a new cable. We’ll talk more about those consoles below, but the short version is, if you want 4K120 and you have a new TV that can handle that resolution (older TVs almost universally can’t), check out Ultra High Speed HDMI cables.

If you’re having issues getting a 4K source to work with your current TV, especially with HDR, it’s possible new cables will fix that. So if you’re in the market, check out Ultra High Speed cables. They’re a bit more “future-proof” and at this point aren’t that much more expensive than other HDMI cables (at least, in the ~6-foot length most people buy). 

PlayStation 5 and Xbox Series X

You can connect the PS5 and Xbox Series X to any TV you could connect a PS4 and
Xbox One X
to. You don’t need a new TV. You probably don’t need new cables either. Definitely not if you have a 1080p TV. If you have a 4K TV and want to play these new consoles in 4K, your current cables will probably work. You’ll know pretty quickly: If you connect the console and the TV says it’s a 4K signal, you’re good to go. 

There are, however, exceptions that relate to HDMI 2.1. Both new consoles are capable of 4K up to 120 frames per second. Some new TVs can handle this higher frame rate. Almost no older TVs can, even those called “120Hz.” The TV will need HDMI 2.1 to let the console run in all this high frame-rate glory. Your current HDMI cables probably won’t be able to handle 4K120. You’ll need to spend just a little extra on Ultra High Speed HDMI versions.

One final important reminder: if you have a receiver or soundbar in your system, and the game console is connected to that, it too has to be HDMI 2.1 in order to pass 4K120. A chain is only as strong as its weakest link, so to speak. So if your console is 2.1, your TV is 2.1, but your receiver is 2.0, you’ll only get resolutions and features possible with HDMI 2.0. 

See Ultra High Speed HDMI Cables at Amazon

Quick Media Switching (QMS) and Fixed Rate Link (FRL)

With the latest HDMI 2.1b rollout it’s worth discussing some additional new features and terms. First is Quick Media Switching, or QMS, which seems like something TVs should just “do” and not need a new feature and abbreviation. It’s fairly self-explanatory, in that it allows your TV to more quickly switch between content of different frame rates. Any TV that supports VRR (see above) should be able to support QMS. This is specifically about frame rates, not resolutions, but if your TV goes blank for a moment between the menu of a streaming service and the show you want to watch (for example), this should prevent that. 

Both the source and the display will need to be QMS-compatible, but theoretically this could be added via a firmware update to newer devices (most likely those capable of VRR).

While a bit “in the weeds” so to speak, it’s worth putting “Fixed Rate Link” on your radar. FRL is what lets HDMI 2.1 handle ultra-high resolutions and frame rates and is a new way to encode data for transmission across an HDMI cable. All HDMI connections up to this point use TMDS, or Transition-minimized differential signaling. For a description about how that works, you can step back in time to my very first CNET article or check out this more numbers-heavy explanation.

You can think of the HDMI connection like a highway. TMDS has multiple highway lanes of buses that are full of data. Each bus has a tiny portion of the overall image. Additionally, there’s a separate lane that’s just for a traffic cop who helps make sure the buses arriving at the destination (the TV) have the same data inside as they had when they left. FRL has two big changes. First, it repurposes the “traffic cop” lane to also transmit data, if needed. It also uses larger, more efficient buses. This is an oversimplification, but the point is that it’s going to allow the higher resolutions and frame rates initially promised with HDMI 2.1. 

To take advantage of FRL, both a source and a display will need to be compatible. However, all devices that will have FRL-compatibility will still support TMDS. So it’s not something you need to worry about until you’re looking at a new 8K source for your new 8K TV, for example. Which is to say, it’s going to be a while. The good thing is, because FR is just repurposing existing channels, new cables aren’t needed.

Do you need to upgrade?

Probably not. At least, not yet. Right now the only common source that can really take advantage of what 2.1 has to offer are the PS5 or Xbox Series X. If you really need 4K120 in your gaming life, then it’s also worth looking for a TV that can take advantage of that.

If you’re buying an 8K TV for some reason, it’s worth considering getting Ultra High Speed HDMI cables, too. Not because there’s anything that requires that bandwidth now, the consoles notwithstanding, but it can’t hurt for a bit of future-proofing. 

So don’t rush out and buy Ultra High Speed cables unless you’re sure you need them. But if you need new cables anyway, get Ultra High Speed as they’ll offer a bit more future-proofing than other cables. 

One last thing to keep in mind: Not all TVs that claim HDMI 2.1 compatibility are actually capable of everything we’ve discussed. In fact, most aren’t. A TV with a 4K120 input might also have eARC, but not necessarily on the same input. A TV might have eARC, but not have any high frame rate or high resolution inputs. It’s confusing, to say the least. Best to do your homework on what models have what capabilities before you set your heart on something specific. In some cases manufacturers can add 2.1 features to already-sold TVs, but don’t count on this. It’s fairly rare and in some cases not possible because of hardware limitations.

Note: This article was first published in 2017 but is updated regularly with new info.

---

As well as covering TV and other display tech, Geoff does photo tours of cool museums and locations around the world, including nuclear submarines, massive aircraft carriers, medieval castles, airplane graveyards and more. 

You can follow his exploits on Instagram and YouTube about his 10,000 mile road trip. He also has written a bestselling sci-fi novel about city-size submarines, along with a sequel.