HDMI Used To Simplify Our Home Theaters, Now It's Adding Confusion

The complexities of HDMI 2.1 viewed through a new home theater.


This month, I tried to upgrade my home theater setup with an LG C1 OLED television and an HDMI 2.1 receiver. Tried. In doing so, I discovered what a nightmare HDMI 2.1's definition of "compatibility" is. When HDMI arrived on the scene almost 20 years ago, it seemed like a godsend: Instead of having to plug in five cables to get a 480p image with stereo audio, you could just plug in one cable. It was universal, had a directional configuration to make sure you couldn't plug it in upside down, and it just worked. Two decades later, though, HDMI is alive and well but has somehow become needlessly confusing. Instead of a simple spec with complex cables, we're now saddled with one simple cable and a truly baffling set of specs. Listen ye to my cautionary tale and beware the dark woods of HDMI.

What is HDMI 2.1?

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HDMI 2.1 is the latest version of the High-Definition Multimedia Interface connector first unveiled in 2002. The initial HDMI 2.1 spec represented a big jump forward for the connector, allowing a bunch of new features. The HDMI 1.0-to-1.2a jump offered a 4.95 Gbps transmission rate. 1.3 bumped that up to 10.2 Gbps, and 2.0 brought it to 18.0 Gbps. It takes a lot of bandwidth to facilitate some of the modern advancements we've seen, such as 120 frames per second at 4K resolution; HDMI 2.1 is a huge leap forward that enables this, offering support for up to 48 Gbps. The more features you want to pass through that cable, the more bandwidth you need.

Along with that 48 Gbps bandwidth, HDMI 2.1 brings a variety of features. Some are for general use, but a bunch are specifically focused on gaming. General features include the introduction of the enhanced Audio Return Channel, or eARC, which offers easier connection between HDMI displays and audio devices, with greater compatibility across most modern audio formats. HDMI Cable Power lets HDMI devices transmit power through the cable for devices that require extra power to transmit the 48 Gbps bandwidth; this will mostly be a background thing that you won't notice. Quick Media Switching allows for faster transitions between media with the same resolution but different frame rates--for example, a television show filmed at 24 frames per second and a sports broadcast that airs at 60 frames per second, both running at 4K resolution.

Gamers, meanwhile, will be able to use Variable Refresh Rates, which allow your display and source device to come to an agreement on when new video frames are handed off, so that even if your game's frame rate fluctuates, the television or monitor can be ready for that shift and keep the motion smoother than it otherwise would be. Auto Low Latency Mode lets your game console automatically set your television to its gaming mode, which disables all picture processing features and focuses on delivering frames as fast as possible to reduce latency. Quick Frame Transport works to further reduce that latency.

Source-Based Tone Mapping is a new HDR feature specific to HDMI 2.1a that lets the source device--the game console, set-top box, or other media player--handle the HDR tone mapping for better control by the source device over the end picture. The standard also supports 4K resolution at 120 Hz and 8K resolution at 60 Hz. HDMI 2.1a additionally adds support for 10K video for commercial and industrial use.

All of this is to say that the speeds offered by HDMI 2.1 are great--they're enabling many welcome new features that can improve your gaming experience in various ways. But standards around HDMI 2.1 have become extremely messy, making it unintuitive and requiring a great deal of research when shopping for a new TV or receiver.

Attempt 1: Getting the settings right

The first problem I encountered when setting up my new hardware was the result of my receiver. A settings menu on Xbox that outlines features supported by my TV was all green checks except for the ability to play games at 4K 120Hz. Let's set aside for a moment the fact that there are very few games that actually support that--this is about making sure that the thing you spent hundreds and hundreds of dollars on is giving you all of the features you paid for.

Plugging the Xbox directly into the television with a Microsoft-supplied cable worked like a charm, so I knew that it was something in between that was the issue. Using two Microsoft-supplied cables to go from the system to the receiver and the receiver to the television didn't work, either.

The root problem, it turns out, was a setting on the receiver. The Onkyo TX-NR5100's menus could be worse, but they're confusing at best and completely incoherent at worst. A 4K-specific setting on the device required me to change it from "4K Enhanced" to "8K Standard." Looking at other users' experiences with this online, it seems like I'm far from the only one to mistakenly believe that if I wanted to use enhanced 4K functionality with my 4K television, I should enable 4K enhanced mode, instead of 8K Standard, which you would think is for 8K sets. If Onkyo had labeled these more effectively, perhaps using HDMI 2.0 and HDMI 2.1 as the labels, this might've been intuitive, but it was not in the least.

Attempt 2: Tethered to confusion

Enabling this setting turned the red X into a green checkmark in the Xbox settings menu, but enabling 4K 120Hz still wouldn't take--the screen would flicker and reset back to the original setting. Again, a direct connection to the television worked fine here. It was, finally, the cable that allowed the last step to work, getting me up to 4K 120Hz. That other Microsoft-supplied cable was meant to go to my PlayStation 5, while a longer, separately-purchased cable would go from the television to the receiver. The cable was labeled on Amazon as offering all of the HDMI 2.1-specific features you could want. The problem is that it's not a certified cable. There is, it turns out, a badge for that, straight from the HDMI Forum itself:

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Amazon, however, is awash in cut-rate cables available from countless unknown vendors like IVANKY, YAHOUDY, and Sniocko. They're labeled with all of those features, with product names like "48Gbps Ultra High Speed Braided HDMI Cable 2M, Support Dynamic HDR, eARC, Dolby Atmos, 8K60Hz, 4K120Hz, HDCP 2.2 2.3, Compatible with HD TV Monitor" to make sure that every possible term you could search for is accounted for. Not all of these cables are certified, though, and the vast majority of them are advertised with a picture of the HDMI connector.

This isn't a store where you can see that badge right on the box. If it's present, it might be in one of the preview images. Even then, though, most people simply won't know to look for that badge because we've been taught that an HDMI cable is an HDMI cable. Slotting in a certified cable (from Monoprice in this case) solved the issue, but this is going to be a huge pitfall for anyone looking for cables online who doesn't know to watch for that badge.

Attempt 3: Back to the drawing board

The next stage of this story takes us back to the Onkyo receiver. If you look at most HDMI 2.1-compatible receivers, they'll have 2-4 ports, each with 40 Gbps of bandwidth. That's still not the full 48, but it's going to be enough to actually pass all of those features that make HDMI 2.1 appealing. Some manufacturers, though, have opted to cut corners to make HDMI 2.1 receivers more affordable, offering ports that only have 24 Gbps available. That allows most of the signal through, but you won't be able to pass 4K 120Hz images with 10-bit color. There just isn't enough bandwidth there.

That would be fine if these were clearly labeled, but neither I nor the rep who helped me at the site I bought from noticed that the Onkyo receiver we'd picked had this limitation. That's because it's not listed anywhere on the spec sheet for the receiver, nor on the box or included Quick Start guide. In fact, the only place I personally found it was in the download-only manual from Onkyo's site… on page 153.

So this receiver, despite costing hundreds of dollars, carries 60% of the bandwidth that even a knowledgeable consumer would expect based on its specs--a fact that's not clearly labeled anywhere, something that many people aren't going to notice before buying it.

Of course, there are two ways to read that:

  1. Many people aren't going to notice that this is missing, so they won't be bothered by it.
  2. Many people aren't going to notice that this is missing, and that's a problem.

I should note that, of course, Onkyo isn't the only manufacturer doing this; Yamaha has at least one receiver with this limitation, and there are others out there as well.

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And you know who's not doing anything to help this? The very organization in charge of HDMI specifications: the HDMI Forum. This consortium of companies works together to establish what features should be in each new version of the HDMI spec, and we were all excited for the announcement of the long-awaited HDMI 2.1 a few years ago. Now it's here, and we're left shrugging our shoulders. Just as it started to gain somewhat of a foothold, the HDMI Forum did two things.

First, it made the decision to fold the HDMI 2.0 spec into HDMI 2.1. Then the forum announced a new spec, HDMI 2.1a, that adds Source-Based Tone Mapping, a feature meant to assist with displaying HDR content. But the Forum also opted to make optional many of the features that literally make HDMI 2.1 what it is. The HDMI Forum is further exacerbating the problem, too.

"Products can no longer get certified for 2.0, only for 2.1, and also 2.1 features are optional to implement," HDMI Licensing Administration VP of marketing and operations Brad Barmy told Ars Technica back in December 2021. So even if a manufacturer wanted to keep their HDMI 2.0 product honest and easy to read, they quite literally are not allowed to. Barmy confirmed in the same quote that features like VRR and ALLM are optional. In one way, this makes sense--for example, a Blu-ray player or Apple TV wouldn't get any value from either of those gaming-focused features but would be able to make use of eARC and Source-Based Tone Mapping. But it also means that we have to take a "caveat emptor" approach to buying anything with an HDMI port moving forward. The HDMI 2.1 label is not a reliable guide.

This all means that a port and cable that support just 18 Gbps bandwidth and that does not allow HDMI 2.1-specific features like ALLM and VRR can now be labeled as HDMI 2.1. It's no longer enough to look for an HDMI 2.1-compatible device--you have to check the feature list and maybe even the manual, too. The HDMI Forum itself says that with this change, manufacturers will be required to list which features the hardware supports.

As the receiver above shows, though, even that might not be enough. You have to know that these limitations even exist and then scrub forums and tech sites for word of them. There's no way manufacturers are going to make those features easy to find on their carefully-designed box art or their limited Amazon image space. The term "HDMI 2.1" is essentially meaningless at this point, offering only confusion and frustration for tech-minded adopters and ensuring that those who just want to plug something in might never get access to all the features they were promised on the box for their TV equipment.

In this environment, how is anyone expected to get a fully-functional chain of HDMI 2.1 devices? This is on top of the fact that it can already be hard to tell both what kind of HDMI you need to get all the features going and what HDMI versions modern televisions support. It might take buying and returning two receivers and two sets of HDMI cables, and lots of troubleshooting, but if you're stubborn enough to outwit the maze of HDMI 2.1, you can get there. But most people probably won't--they'll give up somewhere along the way and just live with it. Or they'll spend a bunch of money to get the latest and greatest, only to get something lesser.

Eric Frederiksen on Google+

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