Think you’ve got HDMI 2.1 figured out? Not so fast. The HDMI Licensing Administrator and associated companies are preparing the next variant, called HDMI 2.1a.

The new version, which the HDMI LA said in a press call this week could be formally launched in some products in 2022, will be backward compatible with all prior versions of HDMI, but not all legacy 2.1 HDMI products (or earlier HDMI versions) necessarily will support the various added feature benefits.

One of the most noteworthy newly added capabilities allowed in the HDMI 2.1a spec is a feature called Source-Based Tone Mapping (SBTM). This enables high dynamic range (HDR)-like picture enhancements from a wider range of products. Both the transmitting “source” device and receiving “display” device must support SBTM to work.

Fortunately, the feature will work with most HDMI cables. Additionally, some (not all) legacy HDMI displays and devices could be made compatible with SBTM via a firmware update, the group said. But whether or not a device (like an AV receiver) can accept this update will depend on how the product was designed and the IC used in the specific model. Stay tuned.

As always, manufacturers selling HDMI 2.1/2.1a (or any HDMI version) products will be required to specify in product marketing materials exactly what features are supported by the specific device. So ignore the version number and read the spec sheets for features carefully before you purchase a product expecting to have SBTM (or any HDMI feature) supported by it.

The HDMI 2.1a spec will enable a source device to assess and adapt HDR output to match a connected display for the best result. Supported sources can include: out-boarded media players, gaming consoles, PCs, set-top boxes and other devices.

The addition of SBTM, like HDR in general, is intended to help boost contrast and brightness performance to the best capabilities of the display device, as not all HDR televisions are created equally. This makes SBTM potentially a nice benefit for compatible mid-range TVs and even some older displays models.

According to the web site: “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.”

“..SBTM allows a source device to combine different types of content (HDR, SDR, dynamic HDR, graphics) together at the same time. For example, when you view a menu of video thumbnails from a streaming video service, some of the thumbnails might be HDR and others might be SDR, and the menu is rendered using graphics. To optimize the quality of the combined content, processing is needed in the source device that cannot be performed inside the display.”

SBTM can also be used by PCs and gaming devices to automate manual user optimization for HDR.

SBTM works alongside current HDR profiles like HDR10, HDR10+, Dolby Vision and HLG. It is an additional intelligent link that facilitates communication between the display and source, working much like Extended Display Identification (EDID) technology and HGiG already supported in some HDMI-supporting products.

Meanwhile, expect more products coming to market in 2022 to support more features of the HDMI 2.1. Before buying a home theater or advanced gaming product, make sure the spec sheet or advertising specifically lists the feature you are expecting to use

In addition, to stay future-ready (or to play the most advanced video games today), it’s a good idea to make sure any HDMI cables purchased from here on is labeled Ultra High Speed (8K/48Gbps) HDMI. It will be required if you intend it support forthcoming high frame rate (48Gbps) next-generation 8K (or 4K/120fps) video games and video content. Look for the authorized Ultra High Speed HDMI certification label to ensure compliance with this bandwidth.

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According to the, the HDMI Specification 2.1a includes support for “a range of higher video resolutions and refresh rates including 8K60 and 4K120, and resolutions up to 10K. Dynamic HDR formats are also supported, and bandwidth capability is increased up to 48Gbps.”

But not all HDMI 2.1a labeled products will include all of the supported features.

According to the, some of these new and previously announced features include the following:

  • “Higher video resolutions support a range of high resolutions and faster refresh rates including 8K60Hz and 4K120Hz for immersive viewing and smooth fast-action detail. Resolutions up to 10K are also supported for commercial AV, and industrial and specialty usages.
  • Dynamic HDR support 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.
  • Source-Based Tone Mapping (SBTM) is a new HDR feature that allows a portion of the HDR mapping to be performed by the Source device instead of the Display device. SBTM is especially useful in cases where HDR and SDR video or graphics are combined together into a single picture, such as picture-in-picture or a program guide with an integrated video window. SBTM also enables PCs and gaming devices to automatically produce an optimized HDR signal in order to maximize the utilization of the display’s HDR capabilities without manual user configuration of the Source device.
  • The Ultra High Speed HDMI Cable supports the 48G bandwidth for uncompressed HDMI 2.1a 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.
  • 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 2.1a products.
  • Enhanced gaming features ensure an added level of smooth and seamless motion and transitions for gaming, movies and video and include the following:
  • Variable Refresh Rate (VRR) reduces or eliminates lag, stutter and frame tearing for more fluid and better detailed gameplay.
  • Auto Low Latency Mode (ALLM) allows the ideal latency setting to automatically be set allowing for smooth, lag-free and uninterrupted viewing and interactivity.
  • Quick Frame Transport (QFT) reduces latency for smoother no-lag gaming, and real-time interactive virtual reality.
  • Quick Media Switching (QMS) for movies and video eliminates the delay that often occurs when a device changes from one HDMI frame rate to another.

HDMI Cable Power enables active HDMI Cables to be powered directly from the HDMI Connector, without attaching a separate power cable. This makes attaching and using active HDMI Cables as easy as using passive, wired HDMI Cables.

Version 2.1a of the HDMI Specification is backward compatible with earlier versions of the Specification and is available to all HDMI 2.0 Adopters.”

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By Greg Tarr

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