Answer:
HDMI 2.1 adds optional support for variable refresh rate technology, dynamic HDR, DSC, ALLM, up to 10K screen resolution, 4K at 120Hz and many more features.
In December 2017, HDMI Forum revealed the final specifications for HDMI (High-Definition Multimedia Interface) version 2.1.
These include optional support for higher refresh rates and resolutions, as well as support for many additional features, such as:
- Dynamic HDR (High Dynamic Range)
- eARC (enhanced Audio Return Channel)
- VRR (Variable Refresh Rate)
- ALLM (Auto Low Latency Mode)
- DSC (Display Stream Compression)
HDMI 2.1 Supported Resolutions & Refresh Rates
HDMI 2.1 at its full capacity of 48Gbps brings support for screen resolutions up to 10K at 120Hz – that’s 10240×4320 pixels! Apart from that, PC and console gamers get the long-anticipated native 120Hz at 4K support.
For 8K at 60Hz and onwards, you will need Ultra High-Speed HDMI cables with up to 48Gbps. Both the cable and HDMI 2.1 standards will be backward compatible with their previous models.
For everything over 8K at 60Hz, HDMI 2.1 uses DSC (Display Stream Compression), which is an effective form of data rate compression without any impact on the image quality. It increases latency, but the added delay is imperceptible (below 1ms).
HDMI 2.1 Features
Other features of HDMI 2.1 include the support for dynamic HDR, which implements its metadata with optimal brightness, contrast, color and other information on a scene-by-scene or frame-by-frame basis.
Granted that it’s supported by the display, this provides a more engaging viewing experience, unlike static HDR, which offers the same metadata for all scenes of the video.
Furthermore, Quick Frame Transport (QFT) and Auto Low Latency Mode ensure responsive gameplay with the low input lag mode (such as Game Mode on many TVs) being automatically enabled when a PC or a console is detected.
With Quick Media Switching (QMS), black screens that take place when toggling between media sources are shorter, while the enhanced Audio Return Channel (eARC) provides full support, as well as easier control over audio devices and advanced audio formats.
What’s most interesting for gamers, besides the 4K at 120Hz support, is the native support for variable refresh rate technology (HDMI 2.1 Forum VRR), such as AMD FreeSync and NVIDIA G-SYNC.
The PS5 and PS5 Pro consoles, for instance, don’t support Adaptive-Sync, FreeSync or G-SYNC VRR technologies, so you will need a display with HDMI 2.1 VRR support for tear-free gameplay.
HDMI 2.1a
The latest HDMI 2.1a specification adds support for optional Source-Based Tone Mapping (SBTM). This feature should offer a better optimized HDR viewing experience by allowing the source device (such as a console or PC) to adapt to the display’s capabilities.
Both the source device and the display must support SBTM for it to work. Such devices are yet to be released (or updated via firmware), so we’re eager to see how they perform.
Confusing HDMI 2.1 Specification
Keep in mind that all HDMI 2.0 devices are now essentially HDMI 2.1a, even if they don’t support the maximum bandwidth of ‘HDMI 2.1’ (48 Gbps) or some of its features.
So, if you’re looking for a 4K 144Hz monitor, for instance, and want to use it at its maximum refresh rate and resolution without any compression, just seeing that it has an HDMI 2.1a port will not guarantee that – it may be limited to what was previously called HDMI 2.0, that is, 4K 120Hz 8-bit 4:2:0.
You will have to check the monitor manufacturer’s specifications to see whether the features such as VRR, DSC, ALLM, SBTM, etc. are supported over HDMI, as well as how much bandwidth is provided (48G or 40G is enough for a full uncompressed 4K 144Hz 10-bit 4:4:4 signal).
Alternatively, you can check monitor reviews for more information. We go over this in more detail in our misleading monitor specifications you should look out for article.
Do You Need HDMI 2.1?
A lot of users have become somewhat fixated on their new display having one or more HDMI 2.1 ports instead of HDMI 2.0.
PC
In truth, if you’re a PC user, a single DisplayPort 1.4 with DSC will be enough. The main reason to ensure your new monitor has an HDMI 2.1 port is if you want to connect it to a console as well as to your PC.
PS5
In case you have the PS5, you will need HDMI 2.1 in order to get 4K 120Hz.
However, a lot of PS5 games can only output 120FPS at lower resolutions, including 1080p and 1440p, in which case, HDMI 2.0 will do just fine for the PS5 since it can support 120Hz at 2560×1440 as well as HDR and HDMI 2.1 Forum VRR (which is supported on some ‘HDMI 2.0’ devices).
Of course, if it’s a native 4K monitor with a high refresh rate, HDMI 2.1 is still preferable, and since the PS5 doesn’t support DSC, the HDMI port should support at least 32 Gbps (bandwidth cap of PS5’s HDMI port).
HDMI 2.1 ports limited to 24 Gbps that rely on DSC for higher bandwidths will be limited to 4:2:0 chroma subsampling on the PS5, instead of the maximum 4:2:2.
Most gamers won’t mind even if they get 4:2:0 compression, which is only evident as minor fringing when small text is displayed on colored backgrounds.
This fringing is also noticeable with the default 4:2:2 compression of the PS5, since it’s compressed from the native 4:4:4 signal.
Xbox Series X/S
If you have an Xbox Series X or S console, HDMI 2.1 is also needed for 4K 120Hz. However, since Xbox consoles support DSC, you can make do with an HDMI 2.1 port with just 24 Gbps and DSC support.
The main issue with Xbox consoles is that HDR is only supported at 4K UHD. So, if you get a 1440p 120Hz+ HDR monitor with HDMI 2.0, you will have to choose between 1440p 120Hz without HDR or 4K 60Hz with HDR (provided that the monitor supports 4K upscaling at 60Hz).
There are a few exceptions, such as the LG 27GR95QE 1440p 240Hz monitor with a 48Gbps HDMI 2.1 port that supports 4K 120Hz upscaling.
HDMI 2.2
In December 2024, HDMI Forum revealed the new HDMI 2.2 standard with a higher 96 Gbps bandwidth, a bit higher than the maximum of 80 Gbps of DisplayPort 2.1.
It also features a new Lateny Indication Protocol that aims to improve audio and video synchronization.
HDMI 2.2 specification will be available in H1 2025, but there’s no information regarding when we can expect it in new devices, such as graphics cards and monitors.
