Sneak Peek: What We Know About HDMI 2.1

Today’s technology is moving so fast as to make the average consumer’s head spin. Twelve years ago DVD was the best source we had, and the Blu-ray and HD-DVD wars were still on the horizon. Today the rate of advancements is rapid enough to discourage buyers accustomed to keeping their TVs for at least ten years. We’re just now getting our heads around a five-year TV replacement cycle, but early adopters, who like to keep up with all of the latest and greatest, need to contemplate a two-year turn-around.

Welcome to the wonderful world of the 21st century and with it HDMI, the single wire connection that by keeping up with all of these tech changes conveys video and audio to our displays through a single cable. But as our technology continues to demand more, HDMI has had to keep pace.

The key parameter here is bandwidth. HDMI is simply an efficient way to convey data, a system consisting of a transmitter at the source (invariably built into your cable box, streaming device, disc player, gaming console, computer, etc.), a carrier (a single cable in the case of HDMI), and a receiver (built into your display—or into an intermediate component such as an AV receiver). No data transmission system, such as HDMI, cares what features pass through it. It only demands that they require no more bandwidth than it’s capable of.

Up until recently, a maximum HDMI bandwidth of 10.2 Gigabits per second (Gbps) was sufficient for all of our needs, including high definition from broadcast, cable, and Blu-ray disc. The main issue was bandwidth loss over long cable lengths, a concern mainly for those with long runs from an equipment rack to a projector.

With the emergence of 4K Ultra HD, however, with its higher resolution, advanced color, and high dynamic range, HDMI needed more bandwidth. So HDMI 2.0, capable of conveying 18Gbps from the source to the receiver, was introduced in 2013. Its increased bandwidth could now pass UHD video at 4K at up to 50/60 frames per second (fps, sometimes called Hz) and with 10- or 12-bits per color. The previous iteration of HDMI, HDMI 1.4, could carry 4K but only at 24fps in 8-bit color.

HDMI 2.0 could also do HDR, but only with the Dolby Vision HDR format. To accommodate the more widely used HDR10, we had another minor step, to HDMI 2.0a. We even had a brief flirtation with HDMI 2.0b, but before that version had the chance to thoroughly confuse the issue it was subsumed when HDMI 2.1 was announced at the 2017 CES last month. The finalized specifications for HDMI 2.1 aren’t expected until Q2 of this year (that is, by the end of June). Some of the details offered here could therefore change before then. Nevertheless, here’s what we know so far about HDMI 2.1.

The big news is that it’s designed to have a bandwidth of 48Gbps (well over twice the 18Gbps bandwidth of HDMI 2.0 and 2.0a), and employs a new form of HDMI cable called, oddly enough, 48G. The HDMI connectors on this new cable will be the same as the current HDMI connectors, but the cable itself will be upgraded. The new cables will be backwards compatible with all current sources and hardware.

At least part of HDMI 2.1’s advanced bandwidth, however, is achieved by hardware changes at the source and receiving ends, not just in the cable. To get the most from HDMI 2.1, the hardware in the source and the receiver will also be different; you won’t get the full HDMI 2.1 package with the new cables alone.

And as far as we know, the current HDMI versions in your sources, AV receivers, and displays can’t be upgraded to full HDMI 2.1 with firmware alone. It’s possible that firmware upgrades might enable at least some of HDMI 2.1’s features, but don’t assume that they will; this will be specific to the actual source/AV receiver/display and its manufacturer.

What benefits will this higher bandwidth offer? It can convey 4K at a maximum of 120 fps (frames per second, or Hz), in 4:4:4 color (no color compression). It can do 8K at 60 fps (4:4:4) or 120Hz (4:2:0), and other resolutions up to 10K.

In addition, HDMI 2.1 can handle BT.2020 color at a bit depth of up to 16 bits (per color), considerably higher than the 12-bit limit of HDMI 2.0 and 2.0a. It can also do HDR with dynamic metadata at 8K and higher. HDMI 2.0 can convey the dynamic metadata currently offered in Dolby Vision, but only at a maximum of 4K resolution. In addition, it’s our understanding that Dolby Vision’s current compatibility with HDMI 2.0 is due to specific Dolby workarounds that allow it to use that version of HDMI. There are other competitors for dynamic metadata HDR currently vying for future use; they can’t use Dolby’s workarounds for obvious reasons and therefore could benefit from HDMI 2.1. (Dynamic metadata can code HDR differently for each shot or scene, whereas HDR10—currently the dominant HDR format on UHD Blu-ray discs—uses the same static metadata for an entire film.)

In addition, HDMI 2.1 will offer a variable refresh rate (VRR), a real benefit for gaming. It also promises enhancements to the Audio Return Chanel (ARC) feature, which in HDMI 2.1 will be called eARC. These ARC enhancements include increased audio bandwidth that, together with other possible benefits, will allow eARC to carry object-based audio (Dolby Atmos, DTS:X, and the like).

Just because HDMI 2.1 can offer all of these features doesn’t mean that all future sources, displays, and other devices in the source-to-display chain (such as an AV receiver) will provide them. Those decisions will be up to the hardware manufacturers. But the commercial pressures to offer as many of them as possible will be intense, even if some of them might not be needed for years.

What does all of this mean to the average consumer? At present, not much. No current consumer video sources require any help from HDMI 2.1 (though gamers and those who use ARC might disagree). With our current HDMI 2.0a you can watch all the streamed video and Ultra HD video that’s out there in the wild, with or without HDR (Dolby Vision is fine with 2.0; and while HDR10 requires 2.0a, every UHD set with HDR, from major manufacturers, can currently do HDR10).

But the future just might demand that we’ll have 8K video with high dynamic range, 16-bit color, high frame rate, and perhaps other features even now gestating in a development lab somewhere. Such features will demand bandwidth far greater than HDMI 2.0a offers, and HDMI 2.1 appears prepared to leap into the breach.

But one caution here. Past experience tells us that future changes to any technology are inevitable. If you plan to install a new HDMI 2.1 cable in a wall, first check it externally for compatibility, and second use a install it in a conduit so it can be easily changed, if needed, in the future.

I wouldn’t expect to see HDMI 2/7/17 2.1 incorporated into hardware (sources or displays) this year, nor perhaps not even next. But it’s a sure bet that cable-makers will start flogging HDMI 2.1 cables long before that, likely with grandiose claims for their benefits to picture quality. But while they should work just as well as your current HDMI cables, there’s no reason to expect any picture improvements from them with current source material, including UHD as it now stands in resolution, color, and bit-depth—with or without HDR.

Is it possible that the new cables themselves, since they’re designed to carry a wider bandwidth and are thus perhaps less likely to roll off the signal bandwidth over longer distances, might offer relief from the connectivity issues that trouble some of us in our current HDMI 2.0a world? To confirm or disprove that we’ll first have to check out such cables, and I wouldn’t expect to see them for several months, at least.

jjster6's picture

So when will upgrades to my eyeballs be available that will allow me to see better than 4K HDR Ultra-Splendid Video?

DougInNC's picture

"No data transmission system, such as HDMI, cares what features pass through it." I only agree if you replace the word "system" with "cable."

But the HDMI "system" of interconnects, handshaking, and DRM continues to cause problems. My DirecTV DVR recently stopped transmitting digital audio to my AVR when the TV connected to the DVR was powered off. It seems that not getting a handshake for the HDMI system voided my ability to listen to audio from the music channels on DirecTV through my AVR.