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HDMI 2.1b: What you need to know and do you really need it

By Ken Wong - 31 Mar 2024

HDMI 2.1b: What do you need to know and do you need it?

Note: This feature was first published on 29 February 2024.

Make sure you use the right HDMI cable to get the full benefits of HDMI 2.1b. (Image source: Pixabay)

In the ever-evolving landscape of audio/video technology, HDMI (High-Definition Multimedia Interface) standards play a crucial role in delivering seamless connectivity between devices. HDMI 2.1b, the latest iteration, builds upon the foundation laid by HDMI 2.1 which can be considered the last major standards updated that introduced a new cable and upgrades in terms of higher video resolution and refresh rates.

HDMI 2.1a: we barely knew you

SBTM optimises the quality of combined content. (Image source: HDMI Forum)

Before we dive into the improvements brought by HDMI 2.1b, let's briefly revisit HDMI 2.1a. 

This standard brought mainly the addition of a new feature, Source-Based Tone Mapping (SBTM).

According to the HDMI Forum, SBTM (which was developed by the HDMI Forum) is especially useful in cases where a combination of HDR, SDR, dynamic HDR, and graphics overlays are combined into a single picture. What can result in this case is that the display could literally get its signals crossed and result in overly bright or dark areas and/or distorted colours. 

SBTM also enables TVs, monitors, and gaming devices to automatically produce an optimised HDR signal to maximise the display’s HDR capabilities without manual user configuration of the source device.

Advantages of HDMI 2.1b

Enjoy higher resolutions and faster refresh rates. (Image source: HDMI Forum)

The HDMI 2.1b standard was released by the HDMI Forum in August 2023, making it the most recent update of the HDMI specification, laying out support for a range of higher video resolutions, refresh rates, resolutions up to 10K, dynamic HDR formats, bandwidth capability is increased up to 48Gbps, eARC support, enhanced gaming features, and Quick Media Switching (QMS). Let's go through each of them briefly.

  • Higher video resolutions and refresh rates: HDMI 2.1b takes a giant leap forward by offering higher video resolutions that support a range of high resolutions and faster refresh rates including 8K60Hz and 4K120Hz for immersive viewing and smooth fast-action detail. Supported resolutions and frame rates include:

    • 4K50/60
    • 4K100/120
    • 5K50/60
    • 5K100/120
    • 8K50/60
    • 8K100/120
    • 10K50/60
    • 10K100/120

The dynamic HDR image looks more vivid than the SDR image. (Image source: HDMI Forum)

  • Dynamic HDR formats: The HDMI 2.1b Specification supports multiple static and dynamic HDR solutions. A static HDR solution (such as HDR10) uses a single set of metadata to optimise the picture brightness curve of a whole video. On the other hand, a dynamic HDR solution (such as Dolby Vision) uses dynamic metadata to optimise the picture brightness on a scene-by-scene, or even frame-by-frame basis. Since each scene and frame is optimised, dynamic HDR can deliver better picture quality.

eARC allows audio from cable, satellite, streaming or source devices sent to a TV to be sent to an AVR or sound bar through a single HDMI cable. Image source: HDMI Forum.

  • eARC support: enhanced Audio Return Channel (eARC) is the evolution of the Audio Return Channel (ARC) with the difference between the two coming in improvements to bandwidth and speed allowing you to send higher-quality audio from your TV to a soundbar or AV receiver. eARC also supports the latest high-bitrate audio formats up to 192kHz, 24-bit, uncompressed 5.1 and 7.1, and 32-channel uncompressed audio. Object-based surround sound technologies like DTS-HD Master Audio, DTS:X, Dolby TrueHD, and Dolby Atmos are also supported.

VRR eliminates lag, judder and frame tearing to deliver smooth images. (Image source: HDMI Forum)

  • Gaming support: The latest HDMI 2.1b specification delivers gaming features that include support for resolutions of 4K at 120Hz refresh rate, and even 144Hz refresh rates for gaming TVs and monitors, to enable an immersive gaming experience. Additionally, there is also support for gaming-specific features including Variable Refresh Rate (VRR), Auto Low Latency Mode (ALLM), and Quick Frame Transport (QFT).

QMS eliminates the blacked-out image you can sometimes get when your frame rates aren't in sync. (Image source: HDMI Forum)

  • Quick Media Switching (QMS): QMS for movies and videos uses the HDMI Variable Refresh Rate (VRR) to solve a problem. VRR (that was developed for gaming) is used here to allow your TV to quickly switch between content of different frame rates and eliminate the 1-3 second blackout on screen that can occur for example when playing a new video on Netflix and it starts streaming as the device switches to its video mode from the menu options.

What does HDMI 2.1b require?

What you need to look for when buying an HDMI cable for HDMI 2.1b use. Image source: (HDMI Forum)

To achieve full support for HDMI 2.1b and its higher resolutions and refresh rates, you need HDMI 2.1b-certified source and displays. Ono top of that, users would require the higher-bandwidth Ultra High-Speed HDMI cable. The latest iteration of the HDMI cable is the only cable that complies with specifications designed to ensure support for all HDMI 2.1b features including uncompressed 8K@60 and 4K@120. The cable’s increased bandwidth capability supports up to 48Gbps for uncompressed HDMI 2.1b feature support. The cable also features very low EMI emission and is backwards compatible with earlier versions of the HDMI Specification and can be used with existing HDMI devices.

HDMI 2.1b should be less confusing

All the features to look forward to in each standard. (Image source: HDMI Forum)

The adoption of HDMI 2.1 was a mixed bag with TV manufacturers able to claim HDMI 2.1 compatibility without implementing every part of the standard. HDMI 2.1a itself was an optional upgrade with manufacturers able to claim compatibility without implementing it.

Despite the confusion around HDMI 2.1 certification, HDMI 2.1b, looks to be different with the HDMI Forum saying “All products must comply with Version 2.1b of the HDMI Specification and the HDMI 2.1b Compliance Test Specification (CTS); and until the CTS is available and a product has passed compliance testing a product cannot claim to be 2.1b compliant or market that it supports 2.1b features”. Manufacturers can only use version numbers when “associating the version number with a feature or function as defined in that version of the HDMI Specification”. 

Do I really need HDMI 2.1b?

HDMI 2.1b isn't necessary for now, but it's definitely good to have. The main advantage of HDMI 2.1b is that the HDMI Forum has decreed that all products must comply with the specification before they can be claimed to be HDMI 2.1b-compliant or be marketed as an HDMI 2.1b device. This means users can be assured that the device supports all of HDMI 2.1b's features. This wasn't the case with some HDMI 2.1 and 2.1a devices. However, since HDMI 2.1b is still so new, it remains to be seen if this will play out in practice. We'll have to wait and see.

If you are looking to buy a new TV or A/V equipment now, then it probably isn't worth waiting for HDMI 2.1b. That's because apart from the reason above, there's little value in having support for such high resolutions and frame rates because of the lack of content. Most streaming services top out at 4K and 8K content is exceedingly rare and doesn't look like it'll become commonplace anytime soon.

If you are shopping now, our advice would be to look for an HDMI 2.1-certified device and make sure it supports the features you want.

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