Originally released in November 2017, HDMI 2.1 is arguably the most significant upgrade to the HDMI standard.The new HDMI 2.1 bandwidth increases to 48 Gbps, which is 2.67 times the bandwidth of HDMI 2.0 (18 Gbps).

HDMI 2.0 and its newer cousin, HDMI 2.0b, have remained the most common versions of the HDMI standard for the past five years, but since 2019, the TV industry has been the first to pave the way for the latest HDMI2.1, which has become the standard on 8K Ultra HD TVs.The best 4K TVs also feature HDMI2.1 in large numbers;The next generation of gaming consoles, the PS5 and the X Box X series, due out in late 2020, will also come with HDMI2.1.

Originally released in November 2017, HDMI 2.1 is still a relatively new standard, so you don't have to worry too much about the obsolency of your 4K TV, streaming media player, or 4K Ultra HD Blu-ray player.But if you're planning on buying a high-end TV, make sure it comes with an HDMI2.1 port, especially for movies and games.

HDMI2.1 specification overview

HDMI 2.1 is arguably the most significant upgrade to the HDMI standard. Here is an overview of the HDMI 2.1 specs:

Connector physical specifications are the same as today's HDMI, with downward compatibility.

Need better shielding performance.Cables with better EMI resistance.

Bandwidth increased to 48 Gbps, 2.67 times higher than HDMI 2.0 (18 Gbps).

It can carry video signals up to 10K@120fps.

New audiovisual features: dynamic HDR, enhanced audio backhaul channel EARC.

New Game Features: Variable Refresh Rate VRR, Fast Frame Transfer QFT, Automatic Low Delay Mode ALLM, Fast Media Switch.

New video signal compression format: VEAS DSC 1.2a.

More bandwidth

As you increase the resolution of a video signal, the amount of data in that signal increases.The data volume of the 3,820x2,160 4K UltraHD signal sent via HDMI is about 4 times that of the HD 1,920x1,080 signal.If you think of cables as pipes, you'll need pipes larger than 1080p to carry 4K signals.The same is true if you increase the frame rate.You need a larger pipe to transmit images at 60 frames per second instead of 24fps at the same resolution.More images per second, more data.

HDMI2.1, 2.0 and 1.4 bandwidth comparison

The HDMI 2.1 standard increases the maximum uncompressed bandwidth that HDMI cables can handle to 48Gbps and the maximum compressed bandwidth to at least 128Gbps.While it will be some time before the device actually needs that much bandwidth, 18Gbps HDMI2.0 has become a bottleneck in many cases.

For example, transmitting a 4k@60Hz video signal with a 4:4:0 chromaticity secondary sampling and 10bit depth requires 20.05Gbps of bandwidth, which is not sufficient for HDMI2.0 connections alone.

Higher resolution and refresh rate

The increased bandwidth of HDMI 2.1 will support video signal transmission up to 10K (10420x4320). The table below covers most of the new resolutions, chroma sampling, bit depth and refresh rate that HDMI 2.1 single-pair connections allow.

HDMI-2.1 standard supports resolution and refresh rate

You can see 4K@60Hz, the refresh rate above the video signal transmission needs bandwidth is greater than HDMI2.0 of 18Gbps, so 8K TV and high-end 4K TV had better be equipped with HDMI2.1 interface, otherwise it is necessary to connect multiple HDMI2.0 cable (if the TV support).

What are the new features of HDMI2.1

In addition to the huge improvement in resolution and refresh rate, HDMI2.1 has other useful new features.

Dynamic HDR

HDR (High Dynamic Range) is one of our favorite improvements to picture quality since the 4K era. It promises higher contrast and richer colors for video content. The most common HDR format today is HDR10, which uses metadata (the metadata that records the actual brightness level of the video content) to tell the TV how to restore the color and contrast of the image.In the current version of HDR10, there is only one set of this metadata in each video content, and the actual brightness of the video content is bound to vary from scene to scene, so the contrast restoration of each scene is bound to be biased.

The metadata (true brightness levels) of each scene and each frame in dynamic HDR content can be different to better fit a particular scene (or frame).In this way, the way to restore the TV for different scenes will vary according to different metadata.

Example of dynamic and static HDR effects comparison

Some advanced HDR versions of Dolby Vision, HDR10 + and Art HDR already use dynamic metadata and can be delivered over existing HDMI connections but require additional bandwidth. HDMI2.1 adds a new channel for dynamic metadata transmission, which completely solves this problem.

Enhanced audio return channel eARC

Since version 1.4, the Audio Return Channel (ARC) has been part of the HDMI standard.ARC allows you to connect all source devices (Blu-ray, game consoles, etc.) directly to your TV and then use an HDMI cable to transmit sound information to an echo wall, receiver, or other sound system, or connect to the echo wall first and transmit video signals to your TV via an HDMI cable, greatly simplifying cabling.At the same time, you can use the TV remote control to control the echo wall or other audio equipment, instead of using the audio equipment special remote control.

EARC connection diagram

However, ARC currently has some limitations.The limited bandwidth (~1 Mbps) limits the audio quality that can be sent over the audio return channel, making it impossible to send high-quality uncompressed audio to the receiver.

EARC solves these problems and really ensures that the display and receiver are forward-looking.It dramatically increases the amount of bandwidth that an ARC channel can use to 37 Mbps.This is enough to send lossless 5.1 and 7.1 audio, such as Dolby Truehd and DTS-HD MA, which is the carrier signal for Dolby Atmos and DTS: X audio formats.

VEAS DSC 1.2A video streaming compression technology

With the popularity of modern high-bit-rate video, video signals require more and more bandwidth, and it is obvious that a new compression method is needed.The most common method of compressing a video stream is a technique called video stream compression (DSC).DSC, originally developed on computer platforms, cannot efficiently encode most television signals because it is only compatible with RGB-encoded video.The VESA group responsible for maintaining the DSC has released an updated version of the DSC, called DSC 1.2a, which supports a maximum color bit depth of 16 bits and enables native YCbcr 4:2:0 and YCbcr 4:2:2 encoding support without having to first convert to RGB encoding and then compress.

HDMI 2.1 supports this technology, but not all devices that will support HDMI 2.1 support this technology, which multiplies the maximum bandwidth that HDMI 2.1 cables can transmit to 120Gbps without compromising image quality.Only very high resolution, high refresh rate devices require DSC.

Variable refresh rate VVR

Variable refresh rate (VVR) is the feature that gamers are most interested in.It synchronizes the refresh rate of the screen and the signal source (the video card output of the game) for a smoother game experience, reducing or eliminating lag, lags and frame tearing.In other words, when the video card creates an image, there will be fewer buffers for frames, so you won't have to choose between image artifacts and input lag, ideally reducing both.

VVR-enabled TVs have smoother pictures

If that sounds familiar, it's because it's similar to Nvidia's G-Sync and AMD's Freesync, both of which are only available through DisplayPort.It's the VESA version of VVR, just call it VESA-Sync.

Fast frame transfer QFT

Fast frame transfer changes the way images are transferred from the signal source to the display.QFT transmits each frame at a higher rate to reduce latency.The total input delay is the result of a combination of many factors, including the time it takes the monitor to process the image and display it on the screen.QFT does not eliminate input delay completely, but it reduces the delay caused by the transmission time between the source and the display.

Input lag is one of the most important indicators of how a TV can be used for games, and it's a game-friendly feature.

Automatic low delay mode ALLM

Automatic Low Latency Mode (ALLM), also known as Automatic Gaming Mode, is another great feature designed for gamers. The compatible TV automatically turns on the TV's low latency (gaming) mode when it detects that a game is being played.This saves you the trouble of having to turn it on manually every time you start the game.It even knows to play a game, to see the difference between someone playing a game and watching a movie on Y Beta, and to switch automatically as needed.Samsung is leading the industry in this feature, with some 2018 models already compatible.

Fast media switching QMS

Past display devices, such as televisions and monitors, turned the screen black for a few seconds before starting to display a new video when any parameters of the source video changed.This is especially true when playing console games, where the output refresh rate and even the resolution can vary depending on the content.

Fast media switching can solve this problem.If the source and the display device are compatible, the black screen will no longer appear when the source switches video formats, but will be switched to the new source immediately.