HDMI 2.1: What It Is and Why It's the Most Important TV Innovation for Gamers

Each manufacturer’s commitment to HDMI 2.1 is different. However, it’s reasonable to assume that this technology will be more complete and reach many more televisions in the future. TV manufacturers may even implement it for good.

But what makes it so unique? One example is its transfer rate, which increases from 18 Gbps in HDMI 2.0 to 48 Gbps in HDMI 2.1. This technology introduces important innovations that promise to improve our experience when watching movies and, more importantly, when playing video games.

Why Moving From 18 Gbps to 48 Gbps Is Important

The most striking data that the HDMI Forum, the organization in charge of promoting the HDMI standard and defining its revisions, usually offers is the transfer rate of each new iteration. As we mentioned before, HDMI 2.0 works with a bandwidth of 18 Gbps, but HDMI 2.1 reaches 48 Gbps.

As you can see, the difference between these two iterations is incredibly significant. However, to achieve this bandwidth, devices communicating over an HDMI 2.1 link must use one of the new Ultra High Speed certified high-speed cables proposed by the HDMI Forum.

The ability to transfer more information simultaneously between the devices involved in playback is crucial because it allows us to use higher resolutions and refresh rates without degrading color coding.

Resolution and refresh rate impact image quality, but we shouldn’t underestimate the importance of chroma subsampling. This technique reduces the bandwidth needed to transmit images without degrading their quality (or at least not excessively). It makes the video take up less space on storage media by reducing the color resolution without lowering the brightness.

To describe chroma subsampling, we usually use the X:X:X format, such as 4:4:4, 4:2:2, or 4:2:0, among others. It’s better to express it generically as Y’CbCr, where Y’ is the luminance (the amount of light the panel emits to our eyes), Cb is the blue component, and Cr is the red component.

You may also encounter the acronym YUV on the Internet when discussing chroma subsampling. Still, all you need to know is that it means the same as Y’CbCr, although using the latter is preferable.

Understanding what this notation system means is easier than it sounds. Each pixel has a luminance value (Y’), blue (Cb), and red (Cr). To calculate the green color component, one takes the other components as a reference and performs complex calculations. Now, we must imagine a matrix of four-by-four pixels so that the Y’CbCr components define each one. The notation 4:4:4, which gives us the best quality because it doesn’t compress the color and indicates that all pixels are luminance value, blue and red.

However, if, for example, we focus on the 4:2:2 notation, in each of the rows of our four-by-four-pixel matrix, we’ll have four pixels identified by their luminance (there’s no compression here), two alternative pixels identified by their blue component, and two alternative pixels identified by their red component.

Another example: The notation 4:2:0 indicates that we have four pixels identified by their luminance in each of the rows of our matrix and two alternative pixels identified by their blue component. In the next row, we’ll again have four more pixels with their luminance and two alternative pixels with their red component.

In practice, the difference in image quality between 4:4:4 and 4:2:2 isn’t excessive. Even 4:2:0 usually offers pretty high quality. However, it’s worth noting that the difference between one option and the other is more clearly perceived when playing a game than when watching a movie. Fortunately, the graphics cards in the most recent generation of PCs and consoles can accurately detect and activate the most advanced chroma subsampling mode supported by the TV to which they are connected and activated.

HDMI 2.1: The Innovations We're Eagerly Waiting for

Higher Resolution and Refresh Rates

The increased transfer rate introduced in HDMI specification 2.1 allows us to transmit video signals with higher resolutions and frame rates than those proposed in revision 2.0. The new iteration supports the following resolutions and frames per second: 4K@50/60 Hz, 4K@100/120 Hz, 5K@50/60 Hz, 5K@100/120 Hz, 8K@50/60 Hz, 8K@100/120 Hz, 10K@50/60 Hz, and 10K@100/120 Hz.

Remember that it’s essential to use one of the new Ultra HighSpeed certified HDMI cables to transmit 4K@120 Hz and 8K@60 Hz signals, which will probably be the most interesting for video game enthusiasts in the medium term. On the other hand, as far as colorimetry is concerned, which, as we saw in the previous section, clearly impacts image quality, the HDMI 2.1 specification supports the BT.2020 color space with 10-bit, 12-bit, and 16-bit encoding.

It also incorporates VESA DSC 1.2a lossless video signal compression technology, which allows us to achieve resolutions higher than 4K@50/60Hz and 8K@60Hz with 10-bit 4:2:0 color coding, such as 8K@120Hz and 10K@120Hz.

These latter resolutions are far from our current needs. However, it’s worth considering the HDMI 2.1 specification because what seems unnecessary now could be desirable in a few years, especially if we focus on the world of video games. As we’ll see below, some of the innovations introduced by HDMI 2.1 are more interesting for gaming than movie playback.

Dynamic Metadata From External Sources

With HDMI 2.1, we can also send video signals to our TVs, including HDR content described by the dynamic metadata used by the Dolby Vision and HDR10+ standards. Unlike the static metadata of HDR10, which represents the color and brightness level homogeneously for all content, the dynamic metadata tells the TV what the brightness and color should be scene by scene.

Obviously, the image quality offered by dynamic metadata technologies is higher than that of formats that use static metadata, mainly if we focus on the details that the TV can recover in the most illuminated areas. As such, using one of the new Ultra High Speed HDMI cables to transport dynamic metadata is unnecessary. We’ll need them if the signal we’re sending is 4K@120 Hz or 8K@60 Hz. Still, it will be sufficient to use a conventional HDMI High-Speed cable if the signal is of a lower resolution or refresh rate.

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eARC (Enhanced ARC)

This technology is an enhanced version of ARC (audio return channel) hence its name. It allows TVs that use it to send any current high-resolution multichannel digital sound format to our audio devices, whether that's a soundbar, A/V receiver, or other solution. It can even handle Dolby TrueHD, Dolby Atmos, DTS Master, and DTS:X, the most sophisticated multichannel sound formats available today.

Moreover, it doesn’t matter if the high-definition sound comes from an app on the TV itself, from DVB-T HD content, or simply from a game console or any other source that we have connected to our TV. The sound transfer to our sound equipment won’t be a problem, due to the enormous transfer speed made possible by HDMI 2.1 and the new protocol used in the video and audio synchronization process.

Let’s hope that eARC will finally end the annoying lip sync we’ve all suffered from at one time or another. One last interesting note: eARC is compatible not only with the new Ultra High-Speed HDMI cables but also with the more modest High-Speed HDMI cables with Ethernet. Many of the mid-range and high-end TVs on the market already include this technology.

VRR (Variable Refresh Rate)

This feature is exciting for video game fans. With it, we can get much smoother and more fluid images. In fact, this innovation is an adaptive refresh technique related to AMD FreeSync and NVIDIA G-Sync, two technologies that PC gamers are familiar with. Broadly speaking, it synchronizes the images produced by the GPU of the PC or console with those reproduced by the TV, which helps combat annoying issues like tearing and stuttering.

The first deforms the image with a line that crosses it horizontally from one end to the other. The second induces the appearance of small jumps in the cadence of the images that reduce fluidity and can ruin our experience. There’s no doubt that VRR will have a positive impact on the gaming experience.

ALLM (Auto Low Latency Mode)

Like VRR, this feature is especially pleasing to gamers because it significantly reduces latency, the time that elapses between the moment we send a signal from our controller to the console or PC and the moment it's reflected on the TV. Automatic Low Latency Mode allows the connected device to send a signal to the TV to automatically activate this mode, eliminating the need for the user to manually activate it.

QFT (Quick Frame Transport)

QFT is another HDMI 2.1 feature that gamers will love. As we've seen, latency is the time that elapses between when we perform an action with our console or PC controller and when it's reflected on our TV screen. The shorter the latency, the better.

This latency is the sum of the time it takes for the video signal to travel through the console or PC’s output circuits, the time it takes for the interface to carry the signal from the source to the TV, and finally, the time it takes for the TV to process the signal it receives and display it on the screen.

QFT technology can't intervene in the first or last of these three processes because they aren’t related to the HDMI interface, so its goal is to reduce the time it takes to transport the video signal from the source to the TV.

This improvement will probably be gradual (we’ll find out when we can test a TV that implements this innovation thoroughly). Still, any reduction in latency, however small, is welcome, especially if we like games that are more sensitive to this problem, such as first-person shooters or fighting games.

QMS (Quick Media Switching)

In a sense, this technology results from applying VRR, the adaptive refreshing we mentioned earlier, to cinematic content. At first glance, this may not make sense since a movie or show is recorded with a constant frame rate throughout the footage. However, when we play trailers from a streaming service, we often encounter content produced at 24, 50, or 60 Hz.

When the TV plays one of these commercials and then switches to another with a different cadence, it is forced to change the clock signal and resynchronize, causing the screen to go black for one or more seconds. This is precisely what QMS technology avoids by using VRR's ability to accept a variable frame rate.

Final Thoughts on HDMI 2.1

The improvements introduced by HDMI 2.1 compared to the 2.0 revision are numerous and, more importantly, profound. Some of them will improve our experience of watching movies, but there's no doubt that the users who will benefit the most are video game fans. With VRR, ALLM, and QFT, TVs promise to offer an experience much closer to that currently provided by gaming monitors, but with the added advantage of accessing larger screen sizes.

Throughout this article, we’ve seen that major TV manufacturers have already adopted HDMI 2.1 in some of their most advanced models. However, as I mentioned in the introduction, HDMI 2.1 technology will be much more prevalent in the TVs that hit the stores in the future. We’ll keep an eye on them because, like many of you, we’re looking forward to seeing HDMI 2.1 in many more models and at 100% of its potential.

Images | QacQoc | CineDigital

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