What is HDMI 2.1a and what new features does it bring?

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Yet another new HDMI standard will be announced at CES 2022 in early January – HDMI 2.1a.

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That might come as a shock to those who have just invested thousands in a new TV sporting HDMI 2.1 ports, especially if they thought they were future proofed. But, there might not be cause to worry just yet.

We explain what HDMI 2.1a plans to bring to the party and whether it really matters.

What is HDMI 2.1a?

The full HDMI 2.1a standard is yet to be announced by the HDMI Forum, the collective that controls HDMI specifications for the many AV manufacturers. However, The Verge reports that HDMI 2.1a has one small but significant update that manufacturers can implement in future – source-based tone mapping (SBTM).

What is SBTM?

Source-based tone mapping is a technology that enables source equipment, such as a set-top-box or games console, to send the exact HDR tone signal to your HDR-enabled display. Currently, the display itself sets the tone, which can vary based on the quality of the TV or monitor, its brightness, etc.

Usually, it relies on the user calibrating his, her or their TV or monitor to give the best HDR presentation, but with SBTM it should eliminate that step entirely.

In addition, SBTM could allow a display to show different tones on the same screen, depending on the source material. For example, if you have thumbnails of multiple sources on the same screen, some in HDR, others not, the TV or monitor will set a single HDR tone over the lot. But, with SBTM enabled, each thumbnail could be shown as originally intended.

As the HDMI Licensing Administator states on its website, SBTM does not replace HDR standards, such as HLG and HDR10, but it can help simplify optimisation.

Will my TV be compatible with HDMI 2.1a?

It is suggested that manufacturers will be upgrade their existing HDMI 2.1-enabled TVs through a firmware update. However, that might not add all of the new features coming with HDMI 2.1a.

We await the full release notes before we’ll know for sure.

Is there anything else and does it really matter?

One other minor issue is that, like other HDMI standards, manufacturers are unlikely to have to support SBTM to put “HDMI 2.1a” on the TV port or marketing materials. It could end up getting a little confusing.

It’s worth noting though that, bar any other announced features, SBTM sounds like a nice-to-have but far from an essential technology. Other features, such as variable refresh rate and 4K 120Hz, are more important and already included in HDMI 2.1. Your TV’s current ability to play HDR10 and HLG, plus Dolby Vision and HDR10+ where applicable, is unaffected.

We’ll update when the new standard is officially launched during CES 2022.

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