Enlarge / HDMI… porn?

Have you already been through HDMI headaches thanks to differing spec standards? Confused by the differences between HDMI 1.4, HDMI 2.0, and HDMI 2.0a/b? Then get ready for more—but in the case of the upcoming HDMI 2.1 spec, the headaches might actually be worth it.

The new spec, announced Wednesday during this year’s Consumer Electronics Show, is a beast. HDMI 2.1 is going to unlock the kind of throughput and features that should feed delicious content to higher-res, faster-refresh screens for years to come. Let’s dive in to what to expect and when to expect it.

Pixels and refresh rates

This photo is actually from the HDMI Forum's announcement of HDMI 2.1. They cannot wait to blow the minds of stock-photo gamers.
Enlarge / This photo is actually from the HDMI Forum’s announcement of HDMI 2.1. They cannot wait to blow the minds of stock-photo gamers.
HDMI Forum

The first upgrade: more pixels. HDMI 2.1-compatible displays will be able to receive a resolution as high as “10K” from a compatible source device and cable. However, the HDMI Forum has yet to spell out what it means by “10K.” That K-factor could mean a 16:9 multiple in line with the UHD versions of 4K (3840×2160) and 8K (7680×4320). However, since the spec sheet also lists “5K,” the HDMI Forum may be referring to a wider version of an 8K resolution display, at 10240×4320, which some screen makers have opted for. (Thus, 5K would also be a wider take on 4K, with the exact same boost in width ratio.)

Either way, I’m not even going to load my calculator app to tell you how many pixels that is. Bunches of pixels. Oodles, even. The count soundly beats the HDMI 2.0 spec (and its 2.0a and 2.0b siblings), which maxes out at 4K resolution.

What’s more, the HDMI Forum has opened the floodgates to higher frame rates, as each of 2.1’s resolutions (4K, 5K, 8K, and 10K) are able to refresh as much as 120 frames per second. The highest refresh rate currently on the consumer market is 144Hz, which can be found on high-end computer displays. We’re unsure why the new spec didn’t secure that kind of data throughput for at least 4K, especially if the standard is rated to push all of 10K’s pixels 120 times a second.

VRR, coming to HDMI 2.1.
Enlarge / VRR, coming to HDMI 2.1.

The most intriguing update to the HDMI spec might be “Game Mode VRR,” which stands for variable refresh rate. This one’s huge for computers and game consoles, where software often pushes a system to its rendering limits. Usually, that’s when gamers either see “torn” or dropped frames as the hardware in question couldn’t draw a full frame in time for the expected 30Hz or 60Hz refresh. A display built with VRR, much like Nvidia’s G-Sync and AMD’s FreeSync, will be able to natively draw a frame of imagery whenever it’s ready, as opposed to being locked to a refresh cycle.

With the HDMI Forum embracing such variable refresh rates, screen manufacturers will be sure to follow. That’s great news for gamers. Toggling a “V-sync” mode in games is usually necessary to stop annoying screen-tearing artifacts, and this toggle adds a slight delay to when frames appear. That leads to issues like input lag, where your button taps take an extra moment to visually manifest. Less lag means better gaming all around.

HDR and sound

For video, HDMI 2.1 will offer dynamic visual metadata as a standard feature. You may have read about dynamic metadata in our recent feature on HDR, or high dynamic range. This lets content makers wipe the color gamut and luminance defaults on your screen at a given moment, which is useful in rendering sudden shifts to particularly bright or dark scenes in a film. In other words, that romantic nighttime beach scene can take place in one frame, and then a giant surprise explosion can happen in the next, and each can have wildly different baseline color gamut values, making each moment look appropriately and realistically rendered.

Right now, luminance differentials on HDR-enabled TVs aren’t so intense, so dynamic metadata won’t provide a discernible difference. But as screens’ differentials grow to the range of 2,000 nits or more, this will definitely matter. Currently, it only appears in the recently developed Dolby Vision standard, where it’s the biggest advantage over HDR-10.

HDMI 2.1’s inclusion of dynamic metadata appears to be set up so that any other video standard can take advantage of it—and that may lead to a revision of the HDR-10 spec in the future. HDMI 2.1 will also natively support a wider color gamut in the BT.2020 spectrum, along with color depths as high as 10-, 12-, 14-, and an astonishing 16-bit. (No current consumer-grade screen truly supports even a full 12-bit color range.)

Ain't no party like an eARC party.
Enlarge / Ain’t no party like an eARC party.

There’s one more HDMI 2.1 perk, by the way: enhanced Audio Return Channel, or eARC. The primary change users can expect from this addition is object-based audio support—meaning, your sound system will be able to process and play sounds based on where your speakers are in your room and how many you have, as opposed to being locked to a more static system. This will require that audio from your source device is processed by compatible sound standards.

Don’t run to Best Buy just yet

Let's jack that throughput up, shall we?
Enlarge / Let’s jack that throughput up, shall we?

When should we expect a full HDMI 2.1 ecosystem to land in living rooms? Not for a while, it looks like. The HDMI Forum’s announcement comes well before HDMI 2.1 will be finalized, and the Forum tells device manufacturers that they will have to wait until the vague time frame of “Q2/Q3 2017” to learn its exact makeup.

We expect the 2.1 rollout will largely resemble that of 2.0; that standard took about a full year to really gain traction, and we’re only beginning to see broad support across the full ecosystem of screen makers, content makers, and video playback devices. The TV- and monitor-producing giants have barely started offering shoppers 4K and HDR screens, and compatible content for both is limited as well; 12-bit color and 10K screens seem like pipe dreams for now, and there’s no indication of when that will change.

One of the HDMI format’s strengths has been forward-compatibility, in which older HDMI controllers’ firmware could be upgraded to take advantage of newer standards. Case in point: the PlayStation 4 shipped with an HDMI 1.4 controller, only to be upgraded to 2.0 late last year in order to unlock HDR compatibility. But HDR only requires a small bit of metadata and is therefore an upgrade that a slower-specced controller can handle. 2.1’s huge jump in data throughput will probably mean that many current video cards and game consoles will be left out in the 2.1 cold.

In addition to new screens and compatible video devices to drive them, you’ll need to buy new cables. The HDMI 2.0’s throughput of 18Gbps has been more than doubled for HDMI 2.1, which allows bandwidth up to 45 Gbps. New HDMI 2.1 cables will be backward compatible with HDMI 1.4 and 2.0 devices, but older cables won’t be forward-compatible with the new spec.

We’ll be keeping an eye on HDMI 2.1 as the specification edges toward being finalized later this year.

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