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Turns out that “HDMI 2.1” ports don’t need to actually support HDMI 2.1 features

Turns out that “HDMI 2.1” ports don’t need to actually support HDMI 2.1 features

 December 16, 2021 at 11:23 am   |     Author:   |     Technology  

Newer game consoles like the Xbox Series X and S support additional features on HDMI 2.1 displays, but HDMI 2.1 can mean different things depending on the product you're buying.
Enlarge / Newer game consoles like the Xbox Series X and S support additional features on HDMI 2.1 displays, but HDMI 2.1 can mean different things depending on the product you’re buying.

If you dabble in high-end 8K TV equipment or own one of the newest Xbox or PlayStation consoles, you might be familiar with HDMI 2.1. The latest version of the ubiquitous display spec adds variable refresh rate support, reduces latency, and offers a big bandwidth increase that allows for higher resolutions, higher refresh rates, and greater color depth. At least, it can support those things.

It turns out that TV and monitor makers don’t actually need to support those marquee HDMI 2.1 features to claim HDMI 2.1 compliance. That’s the gist of a report from TFTCentral, which points out that the HDMI 2.1 spec actually fully replaces the HDMI 2.0 spec rather than simply upgrading it. So any manufacturer that supports HDMI 2.0-level features is technically supporting “HDMI 2.1” because the HDMI 2.0 spec doesn’t exist anymore. And the features we think of when we talk about HDMI 2.1—including Fixed Rate Link (FRL) signaling, variable refresh rate (VRR) support, Auto Low Latency Mode (ALLM), and the enhanced Audio Return Channel (eARC)—are technically optional.

“Products can no longer get certified for 2.0 only for 2.1, and also 2.1 features are optional to implement, so popular features like 4k120, ALLM, VRR are not required,” Brad Bramy, VP of marketing and operations for the HDMI LA, confirmed to Ars. “Manufacturers could only implement eARC, for example, and claim to be a 2.1-enabled device.”

Manufacturers that do claim HDMI 2.1 support are required by the HDMI Adopter Agreement to clearly specify which HDMI 2.1 features their devices support, though Bramy acknowledged that this can still be “confusing for consumers” and that individual manufacturers are ultimately responsible for letting people know what they’re getting. This confusion is being compounded by the fact that the “HDMI 2.0” terminology is still in widespread use, even though it has technically been deprecated.

“I think some older products certified under 2.0 just keep their… marketing intact,” said Bramy. “Some [manufacturers] unfortunately think that even if they are certified under 2.1, they should still refer to 2.0 if they haven’t implemented the 2.1 features, thinking that 2.0 is a known feature set. It is also just as confusing claiming 2.1 compliance and still using feature sets from 2.0 and not stating the features supported. So there are multiple scenarios, and they can all be confusing. And that is why the manufacturers and resellers should simply state which features they support. I can tell it is getting more clear as time goes by, but I’m not sure if it will ever be perfectly clear.”

Though this HDMI 2.1 situation is only making the rounds now, none of these facts is technically new—some digging in the Internet Archive Wayback Machine confirms that the HDMI 2.0 section had been removed from the hdmi.org website sometime between February 6 and February 13 of 2019. But there was a period of time when both specifications did coexist on the website, and the November 2017 press release (PDF) announcing the HDMI 2.1 spec didn’t mention that HDMI 2.0 would be going away. This also isn’t how the HDMI Forum handled the jump from HDMI 1.4 to HDMI 2.0, and it’s not how most companies and developers handle it when they release a new version of something.

There is one precedent for this, though it’s not something anyone should want to emulate: the USB Implementers Forum has continually slapped new version numbers on old versions of the USB spec, something that began when “USB 3.0” became “USB 3.1 gen 1” many years ago. The USB-IF has since raised this practice to the level of performance art, with absurd names like “USB 3.2 gen 2×2” and “USB 3.2 gen 1” (which is also USB 3.0).

This kind of naming chicanery is of obvious benefit to hardware manufacturers, who get to claim support for the newest version of a specification even if they don’t technically support all the newest and best features of that specification. These manufacturers are well-represented in the HDMI Forum and the USB-IF, both as members and as part of the former organization’s leadership. But for people who are just trying to buy things that support the features they need, this sort of behavior continues to be confusing at best and intentionally misleading at worst. You can look at Dell, HP, Lenovo, and Acer product pages and see four different terms to refer to the same kind of port: “USB 3.0,” “SuperSpeed USB 5 Gbps signaling rate,” “USB 3.2 gen 1,” and “USB 3.1 gen 1,” respectively. All of these currently are (or have been, at varying points in time) perfectly valid ways to refer to this kind of port.

The situation with HDMI 2.1 isn’t this bad yet, but if the HDMI Forum continues to introduce “new” version numbers that retroactively apply to older versions of the standard, we’ll end up in the same place. For the time being, you’ll just need to be extra careful when buying HDMI 2.1-labeled monitors and TVs if you’re interested in 8K, HDR, higher refresh rates, and other HDMI 2.1-specific features. Some companies are also taking it upon themselves to make it clearer which products support all HDMI 2.1 features, as Microsoft has done with its “Gaming Features for Xbox” monitor labels. But in the long term, I am once again begging standards bodies to just let version numbers mean something.

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