HDMI 2.1a: what changes with the new standard

The group of the world’s leading electronics companies responsible for defining the specifications of the HDMI video connector, the HDMI Forum has been making headlines in recent weeks for laying out some confusing changes. Acting similarly to USB-IF, a body dedicated to USB connections, the association defined that HDMI 2.0 would be terminated and thus incorporated into HDMI 2.1.

The measure caused great uproar, since now TVs and monitors with HDMI 2.1, previously a reference to support content reproduction in up to 4K at 120 Hz, could end up showing lower performance in certain models, which previously contained the name of HDMI 2.0. To top it off, the group also launched a new standard: HDMI 2.1a.

What changes with HDMI 2.1a?

Made official during the Consumer Electronics Show (CES) 2022, HDMI 2.1a is basically a modest revision of the 2.1 standard, as the addition of the letter a suggests. The protocol maintains the features implemented in traditional HDMI 2.1, such as support for 4K screens at 120 Hz or 8K at 60 Hz, with the only difference being the addition of a feature that promises to facilitate the consumption of HDR content: the Source-Based Tone Mapping (SBTM), or Source Based Color Mapping, in free translation.

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Briefly, Tone Mapping is a feature by which electronic devices map a set of colors of greater coverage to be displayed on a display with less coverage of tones, and it is quite common in TVs, monitors, cell phones and other devices that support content in HDR, which requires wider color coverage.

Simply put, the process converts colors from a higher color coverage, such as DCI-P3, to a lower range gamut, such as sRGB, allowing HDR media to be reproduced on SDR screens, which do not support the technology, correctly, without presenting artifacts such as the brightness burst.

Despite being quite functional, the method often requires user adjustments to ensure fidelity and final image quality. SBTM is a technique that seeks to circumvent this problem, by delivering the mapping process to the device’s hands.

In practice, this means that the user will no longer need to make adjustments — the playback device, such as a computer or a video game, will already perform the mapping automatically, establishing communication with the display to configure it.

An interesting point is that SBTM was already one of the requirements for screens that adopted AMD’s FreeSync Premium Pro/FreeSync 2 technology — the difference is that, now, the function will be implemented directly on the HDMI ports, thus being available also for users of graphics chips from other companies.

The rest of the capabilities of HDMI 2.1 are also present in HDMI 2.1a, including:

  • Dynamic HDR, which makes scene-by-scene adjustments to color, contrast, brightness and other aspects;
  • Auto Low Latency Mode (ALLM), which activates the TV or monitor’s lowest latency settings automatically;
  • Support for refresh rates between 50 Hz and 120 Hz;
  • 32 audio channels;
  • Bandwidth of 48 Gb/s.

Attention to HDMI and Embedded Features

An important point to highlight, and reason for the heated discussions that occurred recently involving the HDMI protocol, was the aforementioned junction of the HDMI 2.0 protocol with HDMI 2.1. Asked about the reasons for this to be done, the HDMI Forum explained to the portal TFTC Central that the HDMI protocols are “a set that contains all the previous standards”.

This means that the features of HDMI 2.0 have become requirements of HDMI 2.1, while the features added with HDMI 2.1 are actually optional. Likewise, when it is released, the HDMI 2.1a protocol will absorb the 2.0 and 2.1 protocols, as they are the same set, but will not require manufacturers to adopt new features, such as the SBTM itself.

The association also argues that “standards have always worked that way”, and that this format in which certain features are optional gives manufacturers greater flexibility to implement what they see fit depending on the segment in which the product is fitted. Other than that, the group also says that companies are required to list which features are supported by the hardware and make them well explained to users.

Therefore, when buying a new monitor, TV or other device that works with HDMI, it is necessary to pay extra attention to make sure that the device supports the full list of features offered by HDMI 2.1a. Check the list of specifications released by the brand, and, in case of doubt, search for specialized sites that bring more extensive technical sheets.

Also be careful when purchasing a cable, which must meet certain requirements to deliver the full performance of the HDMI 2.1 or 2.1a standard. The accessory must be identified as “Ultra High Speed ​​HDMI Cable” on the box and on the body itself, in addition to having a holographic seal with a QR Code that certifies its capabilities.

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