HDMI Inc. Releases HDMI™ 2.1 – 48 Gbps Standard Overview

Originally released in November 2017, HDMI™ 2.1 is arguably the most significant upgrade to the HDMI™ standard. Its 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. Since 2019, the TV industry has been the first to pave the way for HDMI™ 2.1, which has become the standard on 8K Ultra HD TVs. The best 4K TVs also feature HDMI™ 2.1 in large numbers, and the next generation of gaming consoles, the PS5 and the Xbox Series X, due out in late 2020, also come with HDMI™ 2.1.

Because HDMI™ 2.1 is still a relatively new standard, you don't have to worry too much about the obsolescence 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 HDMI™ 2.1 port, especially for movies and games.

HDMI™ 2.1 Specification Overview

Connector physical specifications are the same as today's HDMI™, with downward compatibility.
Needs better shielding performance and cables with better EMI resistance.
Bandwidth increased to 48 Gbps, 2.67 times higher than HDMI™ 2.0 (18 Gbps).
Can carry video signals up to 10K@120fps.
New audiovisual features: dynamic HDR and enhanced audio return channel (eARC).
New gaming features: Variable Refresh Rate (VRR), Quick Frame Transport (QFT), Auto Low Latency Mode (ALLM), and Quick Media Switching.
New video compression format: VESA 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 a 3,840x2,160 4K Ultra HD signal sent via HDMI™ is about four times that of an HD 1,920x1,080 signal. If you think of cables as pipes, you'll need pipes larger than those for 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 means more data.

HDMI™ 2.1, 2.0 and 1.4 Bandwidth Comparison

The HDMI™ 2.1 standard increases the maximum uncompressed bandwidth that HDMI™ cables can handle to 48 Gbps and the maximum compressed bandwidth to at least 128 Gbps. While it will be some time before devices actually need that much bandwidth, the 18 Gbps of HDMI™ 2.0 has become a bottleneck in many cases. For example, transmitting a 4K@60Hz video signal with 4:4:4 chroma sub-sampling and 10-bit depth requires 20.05 Gbps of bandwidth, which is more than an HDMI™ 2.0 connection alone can provide.

Higher Resolution and Refresh Rate

The increased bandwidth of HDMI™ 2.1 supports video signal transmission up to 10K (10240x4320), covering most of the new resolutions, chroma sampling, bit depths and refresh rates that an HDMI™ 2.1 single-pair connection allows. For video signals above 4K@60Hz, the required bandwidth is greater than HDMI™ 2.0's 18 Gbps, so 8K TVs and high-end 4K TVs should be equipped with an HDMI™ 2.1 interface; otherwise it is necessary to connect multiple HDMI™ 2.0 cables (if the TV supports it).

New Features

Dynamic HDR

HDR (High Dynamic Range) is one of the most welcome picture-quality improvements since the 4K era, promising higher contrast and richer colors. The most common HDR format today is HDR10, which uses metadata recording the actual brightness level of the content to tell the TV how to restore color and contrast. In HDR10 there is only one set of this metadata per video, but actual brightness varies from scene to scene, so contrast restoration for each scene is inevitably biased. With dynamic HDR, the metadata of each scene and frame can differ to better fit a particular scene or frame. Advanced formats such as Dolby Vision, HDR10+ and Advanced HDR already use dynamic metadata over existing HDMI™ connections but require additional bandwidth; HDMI™ 2.1 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 lets you connect all source devices (Blu-ray players, game consoles, etc.) directly to your TV and then use an HDMI™ cable to transmit sound to a soundbar, receiver, or other sound system—or connect to the soundbar first and pass video to the TV via HDMI™—greatly simplifying cabling. You can also use the TV remote to control the soundbar or other audio equipment instead of a dedicated remote.

Frequently asked questions

When was HDMI™ 2.1 released and which devices actually use it?

HDMI™ 2.1 was originally released in November 2017. From 2019 the TV industry led adoption, and it became the standard interface on 8K Ultra HD TVs, with large numbers of the best 4K TVs also carrying it. The next generation of games consoles, the PS5 and the Xbox Series X, shipped with HDMI™ 2.1 as well.

Does HDMI™ 2.1 make my existing 4K TV or Blu-ray player obsolete?

No. HDMI™ 2.1 is a relatively new standard, so there is no need to worry about a 4K TV, streaming media player or 4K Ultra HD Blu-ray player becoming obsolete. The advice applies when you are buying new: if you are shopping for a high-end TV, make sure it has an HDMI™ 2.1 port, especially for movies and games.

Why does 4K need so much more bandwidth than 1080p?

Because there is far more data in the signal. A 3840x2160 4K Ultra HD signal sent over HDMI™ carries about four times the data of a 1920x1080 HD signal. If you think of cables as pipes, 4K needs a bigger pipe than 1080p. Frame rate does the same thing: 60 frames per second needs a bigger pipe than 24fps at the same resolution.

Do I need HDMI™ 2.1 on the TV for an 8K or high-end 4K setup?

Yes. Any video signal above 4K 60Hz needs more bandwidth than HDMI™ 2.0's 18 Gbps can supply, so 8K TVs and high-end 4K TVs should be equipped with an HDMI™ 2.1 interface. The alternative, where a TV supports it, is connecting multiple HDMI™ 2.0 cables, which is clumsier than using a single HDMI™ 2.1 link.

What is dynamic HDR and how is it better than HDR10?

Dynamic HDR lets the brightness metadata change from scene to scene and frame to frame. HDR10, the most common format, records only one set of metadata for the whole video, so contrast restoration for each individual scene is inevitably biased. Dolby Vision, HDR10+ and Advanced HDR already use dynamic metadata but need extra bandwidth; HDMI™ 2.1 adds a dedicated channel for it, which solves the problem.

What does the Audio Return Channel do, and how long has HDMI™ had it?

ARC has been part of the HDMI™ standard since version 1.4. It lets you connect source devices such as Blu-ray players and game consoles directly to the TV and then send sound back over one HDMI™ cable to a soundbar, receiver or other sound system, or connect to the soundbar first and pass video on to the TV. It greatly simplifies cabling and lets one remote control the audio equipment.