The HDMI standards are a mess. HDMI 2.1, in particular, is a uniquely frustrating mess, with haphazard support among TV manufacturers, cable makers, and devices that make setting up, say 120Hz gaming on a PS5 or Xbox Series X a uniquely harrowing experience.
Fortunately, the HDMI Forum is swooping in ahead of CES with its latest revision to the HDMI specification stack, HDMI 2.1a, which is here to make everything better and simpler.
... I’m kidding, of course. It’s gonna make things more complicated. It’s a new HDMI standard, what on earth did you expect?
Let’s start with the good: HDMI 2.1a is an upcoming revision to the HDMI 2.1 stack and adds a major new feature, Source-Based Tone Mapping, or SBTM. SBTM is a new HDR feature that offloads some of the HDR tone mapping to the content source (like your computer or set-top box) alongside the tone mapping that your TV or monitor is doing.
SBTM isn’t a new HDR standard — it’s not here to replace HDR10 or Dolby Vision. Instead, it’s intended to help existing HDR setups work better by letting the content source better optimize the content it passes to the display or by removing the need to have the user manually calibrate their screens for HDR by having the source device configure content for the specific display. Other use cases could be for when there’s a mix of content types, like for streamers (who could have an HDR game playing alongside a window of black and white text), displaying each area of content
The HDMI Forum does note that it’ll be possible for set-top box, gaming companies, and TV manufacturers to add support through firmware updates for HDMI 2.1a and its source-based tone mapping “depending upon their design.” Given the usual trajectory of TV spec updates, though, it seems virtually guaranteed that in the majority of cases, users won’t be getting the new features until they buy a new TV that supports HDMI 2.1a right out of the box (which, as of now, is precisely zero of them, given that the spec has yet to be fully released).
Now here’s the bad: like every other unique HDMI 2.1 feature, including variable refresh rates, automatic low latency connections, and the bandwidth necessary to offer things like 10K resolution or 120Hz refresh rates, SBTM will be an optional feature that manufacturers can support — but not something that they’re required to support.
That’s because the HDMI Forum and HDMI Licensing Administrator (the two organizations that define and license out HDMI standards, respectively) run the standards as a set that contains all the previous standards. As TFTCentral explains, according to the HDMI Licensing Administrator, now that HDMI 2.1 exists, there is no HDMI 2.0 standard anymore: all new HDMI 2.0 ports should be lumped into the HDMI 2.1 branding, despite not using any of the new features included in the “new” 2.1 standard.
HDMI 2.1a will function in a similar manner: once the standard is released, by the HDMI Licensing Administrator’s rules, all new ports will, in theory, be labeled HDMI 2.1a — but they won’t have to offer the new SBTM or even any HDMI 2.1 features. The HDMI Forum’s argument is that this is always how its standards have worked, and that optional features allow manufacturers to have flexibility in what functionality they offer (an entry-level set, for example, probably doesn’t need ports that support 8K 120Hz VRR gaming). And the group says companies are required to list what features their hardware supports so that it's clear to customers what their hardware is capable of, beyond the number expectation.
That argument doesn’t really hold up, though. The whole point of standards is that they’re meant to simplify this sort of thing by, you know, standardizing it across devices — if you have to dig into a spec sheet to figure out if the specific refresh rate feature you want is supported on a new TV, why bother with the HDMI 2.x branding in the first place?
Even better, TFTCentral’s report notes that most manufacturers aren’t following the HDMI licensing recommendations for port labeling. At least for now, TV companies have for the most part still listed HDMI 2.0 ports as “HDMI 2.0” and reserved the HDMI 2.1 labeling for ports that actually support the newer features. But the crucial issue is that under the rules of the organization that licenses out the standard, these companies don’t have to do this — and technically, shouldn’t be labeling things like this, despite the fact that it’s more helpful to customers. This means that there is a chance less scrupulous (or simply more ignorant) companies could start to market HDMI 2.1 ports that don’t actually offer any 2.1 or 2.1a features.
That leaves the upcoming HDMI 2.1a standard and its new SBTM feature in much the same place as the rest of HDMI 2.1 and its feature set: a potentially helpful new feature that could make the content you watch and play look better, but that will likely require buying new hardware and cables, and which may not even be actually supported by devices that claim to have “HDMI 2.1a” ports. That means that as CES 2022 and its slew of TV announcements are about to arrive, the only way to make sure that you’re getting the HDMI features that you want is to — as always — make sure to read the fine print.