A Guide to HDMI 2.1

Originally published 7 November 2020. Last updated 13 December 2021

Introduction

If you follow the graphics card, display or console gaming market you’ve probably all heard talk about HDMI 2.1. This is the latest HDMI connection standard which follows on from previous widespread HDMI 1.4 and HDMI 2.0 generations, and can offer increased bandwidth and capabilities to support modern and future display capabilities. HDMI 2.1 was actually confirmed a long time ago, back in November 2017 but it only really started to appear properly in the market during late 2020 and on in to 2021. We’ve already seen a range of modern TV’s equipped with this new connection, including the LG CX OLED which we reviewed, and their follow up LG C1 OLED which are a popular option for some gaming and multimedia enthusiasts, even in the desktop monitor space. We have already seen the first generations of graphics cards released with this new option, and the latest-generation games consoles like the Sony PS5 and Microsoft Xbox Series X also now use this connection. We will explore here what HDMI 2.1 can offer, some areas to look out for with the advertising of this term, what has been seen so far and most important (to us at least) what we can expect from the desktop monitor market in the future.

Image courtesy of HDMI Licensing Administrator, Inc.

The Physical Interface

The physical connection type remains the same as older HDMI 1.4 and 2.0 generations and the port is backwards compatible with older generation devices. So if you have for instance a console or Blu-ray player device with an HDMI 1.4 output, you can still use that and the same HDMI cable connected to a v2.1 port on a modern display if you want and it should work fine.

If you have a source device that outputs over HDMI 2.1 (like a next generation games console or new graphics card), then likewise you can connect this to a display with the older HDMI 2.0 if you want, but it will not be able to support the full bandwidth and capability as if it were HDMI 2.1 on both. To take full advantage of the capacity and bandwidth that HDMI 2.1 offers you need that to be present end to end.

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Resolutions and Refresh Rates

 
Summary of supported resolutions and refresh rates. Image courtesy of HDMI.org

HDMI Specification 2.1 is capable of supporting a significantly higher bandwidth than 2.0, offering a big jump from 18 Gbps to 48 Gbps max. Pay attention though to our later section in this article, as this increased bandwidth is actually optional! HDMI 2.0 used a signalling method called “TMDS” (Transition Minimised Differential Signalling) which could deliver that max 18 Gbps bandwidth. HDMI 2.1 as a standard can support “FRL” (Fixed Rate Link) signalling which can reach up to 48 Gbps.

This even puts it beyond the bandwidth of current DisplayPort 1.4 connections and makes it an interesting new option right now. It supports a range of higher video resolutions and refresh rates than older generations of HDMI including:

• 4K resolutions at 120Hz – supported without any compression needed (like chroma sub-sampling or Display Stream Compression/DSC usage). This includes at 4:4:4 full RGB and with 12-bit colour depth. You can even push as high as 16-bit if you use DSC as well.
   
• 5K resolutions at 120Hz – also supported in the same way although only up to 8-bit colour depth with 4:4:4 full RGB. To get to 10-bit or 12-bit colour depth at 5K 120Hz you will need DSC to be used.
   
• 8K resolutions – supported at a range of refresh rates and colour depths, although DSC will be required for some of the higher levels as outlined in the table below. Up to 30Hz is supported without any further compression needed. To get to 60Hz you will need DSC, unless you’re willing to drop chroma a lot to 4:2:0. To get to 120Hz you will need DSC but it is achievable at 8-bit colour depth without further chroma sub-sampling.
   
• Resolutions up to 10K – also supported for commercial AV, and industrial and specialty usages. 60Hz and above will require DSC and some will also require additional chroma sub-sampling.
   

Summary tables above courtesy of HDMI.org

Other Supported Features

Summary of capabilities courtesy of HDMI.org

There are several other important features that are supported from HDMI 2.1, not available with older generations. Again these are actually optional extras, pay attention to our later section discussing this confusing area. The optional supported features include:

• Dynamic HDR formats supported which ensures every moment of a video is displayed at its ideal values for depth, detail, brightness, contrast and wider color gamuts—on a scene-by-scene or even a frame-by-frame basis.
   
• eARC simplifies connectivity, provides greater ease of use, and supports the most advanced audio formats and highest audio quality. It ensures full compatibility between audio devices and upcoming HDMI 2.1 products.
   
• Enhanced gaming and media features ensure an added level of smooth and seamless motion and transitions for gaming, movies and video. They include:
  • Variable Refresh Rate (VRR) – something which hopefully you are all familiar with by now, importantly including the so-called “HDMI-VRR”
  • Auto Low Latency Mode (ALLM) – ALLM detects when a connected game console is turned on, switching to game mode on the TV automatically when that happens. Since game modes are designed to provide the lowest latency, mostly by removing a lot of the image processing that’s performed on other modes, you’ll get shorter input lag between the console and the screen, resulting in faster response times. Having the TV sense this and make the switch automatically is a huge convenience for anyone who just wants to jump into a game quickly.
  • Quick Media Switching (QMS) for movies and video and also Quick Frame Transport (QFT) which reduces latency for smoother no-lag gaming, and real-time interactive virtual reality.
     

Cable Requirements

Image courtesy of HDMI.org

Supporting the 48Gbps bandwidth is the new Ultra High Speed HDMI Cable. The cable ensures ultra-high-bandwidth dependent features are delivered. It features exceptionally low EMI (electro-magnetic interference) which reduces interference with nearby wireless devices. The cable is backwards compatible and can be used with the existing older generation HDMI devices. These cables are more expensive than HDMI 2.0 cables although likely to get cheaper over time of course. Sony and Microsoft include an Ultra High Speed cable with their consoles, and most monitors we have seen with HDMI 2.1 ports so far also include one in the box.

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Image courtesy of HDMI.org

Reasons for HDMI 2.1 Adoption

There are some key drivers for the adoption of HDMI 2.1 in the various spaces:

• Games Consoles have opted to stick with the HDMI standard and made use of the additional features that 2.1 can support in order to offer the latest and greatest capabilities like 4K @ 120Hz and 8K resolutions. The extra bandwidth capacity compared to v2.0 provides them more headroom for the latest games, powered by their new devices and technologies. It will also allow support for features like variable refresh rates (VRR) and auto low latency mode (ALLM). You can read our How to Buy a Monitor for PS5 or Xbox Series S/X article for a lot more information about the new consoles and their features.
   
• TV’s want to support HDMI 2.1 since HDMI has long been the standard in that segment, and they don’t feature DisplayPort. The typical devices that connect to TV’s like games consoles, Blu-ray players and TV devices are pretty much all HDMI and so that’s the norm in the TV space. TV’s want to use the new capabilities of HDMI 2.1 to handle the latest features like 4K @ 120Hz, 8K resolutions, HDR and VRR. This is also partly driven by the fact that next generation games consoles from Sony and Microsoft have selected HDMI 2.1 as their output connection to maximise potential, and so TV’s need to keep up with that.
   
• Graphics cards are used primarily to power desktop monitors and DP has been the standard and the preference in that space for a long time. In the absence of DP 2.0 which is not ready yet, graphics card vendors have adopted HDMI 2.1 in order to offer the latest capabilities discussed in this article and the highest current bandwidth potential. There is some small but growing demand for graphics cards to support PC gaming from modern TV’s where HDMI 2.1 is featured but DisplayPort isn’t, so it’s useful to have HDMI and not focus entirely on DP. For PC gaming this is mainly a stop gap though until DP 2.0 arrives in the graphics card space, although we of course expect HDMI 2.1 to be kept anyway although less relevant as an output option once DP 2.0 is here.
   
• Monitors want to support HDMI 2.1 to again cope with the latest bandwidth capability from a PC graphic card which goes a bit beyond what DisplayPort is capable of. We talk about this in more detail later in the displays section but HDMI 2.1 is likely to be more focused in the 4K monitor space to accommodate next generation games consoles. It is less important and useful for lower resolution monitors (although could still be handy for some features) and less important for PC gaming given the focus in that space on DisplayPort and the future arrival of DP 2.0.

Graphics Cards

 
NVIDIA RTX 3000 series, Image courtesy of NVIDIA.com

It is only since the later months of 2020 that we have even seen HDMI 2.1 appear on commercially available graphics cards to offer this output from PC’s. NVIDIA were the first to market with their latest RTX 30 series cards, like the top-end 3090 for instance. These have been in hot demand since their launch and provide support for all the latest PC graphics features including 4K @ 120Hz without compression and 8K resolutions.

As a side note and not specifically related to HDMI 2.1, these new generation of NVIDIA cards will also support their new NVIDIA Reflex features, including the G-sync monitor specific Reflex Latency Analyzer technology. The Asus ROG Swift 360Hz PG259QNR, a slight update to the PG259QN we reviewed, was the first screen to feature this new technology. TFTCentral have now added an RTX 3090 to our test system to support all future testing of HDMI 2.1 and other discussed features in our reviews.

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AMD Radeon RX 6000 Series, image courtesy of AMD.com

The slightly later announced AMD Radeon RX 6000 series cards also support HDMI 2.1. It’s good to see new cards finally emerging that will offer this new connection, and support future capabilities discussed above. You need to keep in mind you’re going to need to fork out a lot of money for a top end graphics card if you want the latest and greatest features, including HDMI 2.1. It will be a while before mid-range and mid-priced cards offer this connection more widely.

What about DisplayPort?

In the desktop PC gaming space DisplayPort has been the main focus for delivering high bandwidth connections from graphics card to desktop monitor, and has usually been ahead of HDMI in terms of capability. For instance the current DisplayPort (referred to from here as “DP”) 1.4 standard supports 32.4 Gbps bandwidth compared with HDMI 2.0 which has 18 Gbps. DisplayPort has been the preferred connection for delivering top end features including G-sync/FreeSync, high refresh rates etc.

HDMI has now crept ahead of DP with HDMI 2.1 capable of offering bandwidths up to 48 Gbps. So will this become the standard for graphics cards and monitors? Not in the long term. DisplayPort 2.0 has already been announced and will up the bandwidth support further to 77.4 Gbps. It’s not available yet but we would expect this to be the focus in the future of graphics card and monitor manufacturers.

Games Consoles

From a Games Console point of view the Sony PlayStation 5 and Microsoft Xbox Series X include HDMI 2.1 outputs, and will be able to support features like 4K @ 120Hz and 8K resolutions (8K @ 60Hz), variable refresh rates (VRR) and ALLM – although don’t expect there to be widespread game support for these kind of things straight away. With the next generation of consoles if you want to make the most of their capabilities, you will want a screen that has HDMI 2.1 and that includes support for these features. These new consoles are going to be a key driver in display manufacturers adopting HDMI 2.1 as well, both in the TV and monitor space.

You can read our How to Buy a Monitor for PS5 or Xbox Series S/X article for a lot more information about the new consoles and their features.

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HDMI 2.1 Displays

 
LG CX OLED

We won’t attempt to cover the TV’s that exist already with HDMI 2.1 but there are quite a few available from LG, with HDMI 2.1 featured on all of their C9, CX and C1 OLED TV’s for instance (see our review of the LG CX OLED as a desktop monitor). Samsung have also offered it on their Q90 LED display, and we’d expect many more TV’s to follow in the coming months and years. With next generation games consoles featuring HDMI 2.1 it is arguably more important in the TV space for HDMI 2.1 to be included, given that this is the primary display type for those kind of gamers.

We have now started to see a range of desktop monitors released with HDMI 2.1 included. We’ve already reviewed models such as the Gigabyte Aorus FI32U, Asus ROG Swift PG32UQ, AOC AGON Pro AG324UX and Eve Spectrum 4K. It should be noted that the support for higher bandwidths and gaming features like HDMI-VRR and ALLM really does vary so far. It’s important to remember that just because a screen lists HDMI 2.1, that on its own doesn’t really mean anything! (see following section). You can also search our news page for articles about forthcoming screens with HDMI 2.1 featured.

Less important for the PC gaming space

While HDMI 2.1 can offer a bit more bandwidth, DisplayPort is still the primary connection type in the graphics card and monitor space. You can already achieve 4K @ 120Hz for instance at 4:4:4 RGB over DisplayPort 1.4 when using Display Stream Compression (DSC) which is lossless visually. DisplayPort is also used for VRR on PC’s including NVIDIA G-sync and AMD FreeSync, and as we’ve discussed above DisplayPort 2.0 will also arrive at some point to take over and offer even more capacity. So for PC connectivity the presence of HDMI 2.1 is less important and useful. This might explain why desktop monitors, which are aimed more at PC users, are lagging a bit behind TV’s.
 

Useful but not always necessary for next generation games consoles

With the arrival of next generation games consoles like the PS5 and Xbox Series X, these devices don’t have a DisplayPort output. And so to take advantage of their features in full like 4K @ 120Hz, VRR and ALLM a monitor needs to have an HDMI 2.1 input. Importantly HDMI 2.0 doesn’t have the sufficient bandwidth to support 4K @ 120Hz without colour sacrifice. You might notice that the screens released so far all offer a 3840 x 2160 “4K” resolution. We expect the 4K models to be the priority for manufacturers to provide HDMI 2.1 features and capabilities. Connecting a PC over DisplayPort 1.4 will be fine on those screens, but for the games consoles HDMI 2.0 wouldn’t have been enough. So to use a games console on screens like that you really need HDMI 2.1.

What about lower resolution displays like 1080p and 1440p? There is actually less need to provide HDMI 2.1 capabilities on those monitors, as older HDMI 2.0 TMDS signalling has sufficient bandwidth to handle those resolutions at 120Hz to accommodate games consoles. So if you have a monitor with those lower resolutions, which are far more widely available and popular right now, HDMI 2.0 will be fine to support the high refresh rate output from the console. You won’t be able to use the full 4K resolution output from the console of course, but the monitor isn’t capable of displaying it anyway. So the high refresh rate side of things should be fine even from older HDMI 2.0 displays if you aren’t looking for 4K support.

One thing we should note about resolutions is that the Playstation 5 currently will only support 1080p or 4K output resolutions, and will not support 1440p. So if you have a 1440p screen you are stuck somewhere in the middle. If your 1440p screen also has “virtual 4K” support then that is one option you can use here. You can check this by seeing if you can set your PC to 3840 x 2160 resolution without any custom resolutions being needed. Screens with Virtual 4K support will downscale the 4K input to the native resolution of the 1440p panel still, but that is better than inputting the alternative which is 1080p (that’s already been downscaled by the console), and then letting the screen try and scale that back up. Virtual 4K support on a 1440p resolution monitor can be useful for consoles. The Xbox Series X however can support 1440p resolution output anyway so it’s easier there.

What about variable refresh rates? HDMI 2.0 can also support adaptive-sync/FreeSync over HDMI, which is available from the Xbox Series X like it was on the One X and One S. That means if you are buying an Xbox Series X and have a monitor with 1080p/1440p resolution and 120Hz+ refresh rate, you can use both the high refresh rate and VRR capabilities from the console even over existing HDMI 2.0. You don’t even need HDMI 2.1 there. The Sony PS5 is unfortunately a bit more confusing, as it is does not support either FreeSync or HDMI-VRR output at the moment. It is expected that it will be added at some point but possible it will only feature HDMI-VRR later on which is not supported over HDMI 2.0, and is a feature of HDMI 2.1 capabilities only. That would mean that if you bought a PS5 and connected it to an older HDMI 2.0 monitor with a lower resolution (1080p or 1440p) you could use the high refresh rate fine, but you wouldn’t have VRR support potentially. Right now it looks like HDMI 2.1 will likely be a must for any monitor to support the key PS5 capabilities properly.

You can read our How to Buy a Monitor for PS5 or Xbox Series S/X article for a lot more information about the new consoles and their features.
 

What about Native NVIDIA G-sync hardware module Screens?

These first wave of HDMI 2.1-ready monitors will all feature traditional scalers and adaptive-sync support for VRR, as opposed to any with a Native hardware G-sync module. It remains to be seen what will be supported for future Native G-sync screens, as at the moment the latest v2 hardware module only has DisplayPort 1.4 and HDMI 2.0 connections (1 of each). An updated module from NVIDIA would be needed if they plan to offer HDMI 2.1 capabilities and bandwidths from Native G-sync screens, which you would expect they’d want to. NVIDIA didn’t have any official information they could share with us on this at the moment but it would seem logical to expect an update at some point given their ongoing investment in G-sync and the benefits it brings to gamers.

Don’t assume that the HDMI 2.1 branding means you get all the new capabilities – it doesn’t!

We would encourage you to read our additional article which talks about “When HDMI 2.1 Isn’t HDMI 2.1 – The Confusing World of the Standard, “Fake HDMI 2.1” and Likely Future Abuse“. To summarise, the HDMI 2.1 certification actually replaces 2.0 and the HDMI Licensing Administrator (HDMI org) actually intend for all HDMI 2.x devices to be certified under this scheme, with v2.0 no longer being relevant or available. All of the new capabilities and features we’ve talked about in this article are actually optional, including high bandwidths, FRL signalling, VRR, ALLM and everything else.

This creates an incredibly confusing market, and there is the potential that manufacturers will abuse the new naming scheme and call everything HDMI 2.1 even if it lacks any of the new capabilities that consumers associate with this term – those discussed in this article. In fact they are supposed to, according to HDMI org. What this means is that the HDMI 2.1 name itself is rather meaningless and could start to mean nothing on its own. You cannot assume that a display or any other device marketed with HDMI 2.1 includes any of these new possible capabilities, even if some of them feel like they should be an absolute base-line requirement. What you need to look out for and query is the features that manufacturers list along side this. Look out for confirmation of the bandwidth, the resolution, refresh rate, colour capabilities and support for things like VRR, ALLM and eARC. The absence of these features in the spec probably means they are not supported. It’s a murky and confusing certification unfortunately.

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