HDMI is a confusing mess of standards and ports, with many features optional for manufacturers to implement. For example, even though HDMI 2.0 can support 4K at 120Hz, not all TVs and consoles with HDMI 2.0 are built for that. Now it seems there’s another HDMI update on the way.
According to The Verge (the HDMI Forum has yet to reveal anything), the new HDMI 2.1a standard will be introduced at CES 2022. The main new feature with HDMI 2.1a will be Source-Based Tone Mapping, or SBTM for short, which offloads some HDR tone mapping to the content source (e.g. your console, set-top box, or PC) instead of the TV or monitor doing all the work on its own. The feature will also allow better mixing of HDR and SDR content on the same device. For example, you could be using a video editor that is rendered in SDR, but with the video thumbnails and preview in HDR.
Even though it doesn’t mention HDMI 2.1a specifically, a new page on the HDMI Licensing Administrator’s website describes the new functionality:
Source-Based Tone Mapping (SBTM) enables the source to send a video signal that takes full advantage of a specific display’s HDR capability by adjusting its output to take better advantage of each display’s potential. As with other HDR technologies, rather than adopt a fixed set of color and brightness ranges, SBTM allows the Source to adapt to a specific display. SBTM can also be used by PCs and gaming devices to eliminate manual user optimization for HDR.
The new SBTM feature is reportedly optional for device manufacturers to implement, so unless a TV, monitor, console, or other device says it supports SBTM, there’s no way of knowing for sure — even if it claims to support HDMI 2.1a. Keep an eye out for the first products to support HDMI 2.1a next week during CES 2022, which is increasingly becoming online-only.