Developers of HDMI 2.1, the next version of the HDMI digital connector which was formally announced at CES 2017 earlier in the month, are calling it by far the most aggressive and different of all the prior versions of the digital interface used for video and audio applications.

During our visits with various engineers and executives involved with HDMI 2.1, we gathered a little additional insight beyond the core specs outlined by the HDMI LA two days before the show opened.

The experts, who will not be named, spoke to us on background, primarily because the release of the completed specs to members will not be made until the second quarter of this year. But those involved in the format’s development said it was designed to not only expand the capabilities of HDMI but to improve the quality of the HDMI experience. The developers sought a version that will be reliable and to improve upon brand-to-brand interoperability, which has been an issue from time to time with earlier HDMI versions.

Read more on the coming HDMI 2.1 spec after the jump:

The 2.1 version calls for more than tripling the bandwidth of the prior HDMI 2.0, to 48 Gbps. The lane speed is raised from 6 Gbps to 12 Gbps; the encoding changes from 10B to 16B/18B, and brings about an 11 percent improvement in efficiency.

The connector includes three twisted pairs and a clock – which translates to four twisted pairs but sending basically RGB or Y and Cb and Cr. HDMI 2.1 can be run in inverted clock mode, which uses all four lanes and is packetized – This is said to be similar to though not the same as DisplayPort.

HDMI will also support DSC 1.2 compression for everything higher than 8K with 4:2:0 chroma sub sampling. This can triple the bandwidth or increase the cable length.

“8K gives you 32 megapixels, so that’s just massive,” one source told us.

Additionally, HDMI 2.1 is said to be highly resilient to errors because the link was designed with robust forward error correction built in. When running in compressed mode, even with substantial data loss, a signal can still be received.

In the 4K domain, HDMI 2.1 will handle 4K/120fps, which will be useful to European broadcasters, who want to do high-refresh rate broadcasts. Video can carry high dynamic range (HDR) with frame accurate (aka Dynamic) HDR, so that, for example, when a scene is shot indoors through a window to show a scene outdoors, the dynamic range can be different for what is pictured indoors than it is for what is pictured outdoors. The exact format for Dynamic HDR was not specified for the HDMI 2.1 spec., as several versions are competing for acceptance in the next generation broadcast system standard currently being approved for the United States and various countries around the world.

Nevertheless, it seems apparent that consumers next year will start getting this Dynamic HDR in one form or another and HDMI 2.1 will be ready for it when it comes.

As for forward compatibility with HDMI 2.1 in current televisions and supporting products, some forms of HDR, like Hybrid Log-Gamma (HLG) and Dolby Vision might be possible without the need for the new 48 Gbps cable. But whether or not a 4K Ultra HDTV available today will support HDMI 2.1 signals in the future through a firmware update will depend on the manufacturer and the specific model in question. Some equipment could have been developed with the coming infrastructure in mind to support HDMI 2.1, but thus far no manufacturers are saying so until the completed specification is delivered.

HDMI 2.1 Will Bring Better Audio Performance

In addition to supporting video, HDR 2.1 will support much more robust high resolution audio formats, including object oriented audio, which can be sent over a new and improved Enhanced Audio Return Channel (eARC) feature.

According to sources familiar with the development process, Lattice Semiconductor developed most of the HDMI 2.1 specification, but it was written to the requirements of the HDMI Forum, with much input from high-end audio companies and the forums working with various audio compression technologies. According to one insider, “the audio companies are big competitors with each other but in setting these standards they worked together very closely. It’s going to make home theater a lot better.”

In HDMI v.1.4, Audio Return Channel and HDMI Ethernet were made available over one channel. But where ARC became a hit and widely used, HDMI Ethernet flopped. Since the development of HDMI 1.4, a number of advancements have occurred. The bandwidth of streaming audio has gone up, and a lot of the streaming video services are moving to Dolby Digital Plus, which requires greater bandwidth and is stretching the limits of ARC.

For audio purists who like to use HDMI ARC, here is a tip one HDMI developer gave us: Even when using ARC today it is much better for audio performance to do it using an HDMI Ethernet cable because pins used for Ethernet in the HDMI Ethernet cable are shielded.

This is important because, when using ARC, the source might have an HDCP connection. HDCP toggles the DDC pin. That toggling can cause noise on an unshielded ARC channel which can be heard on the system speakers. But if you use an HDMI Ethernet cable it will be shielded and immune to the interference of DDC toggling.

The primary difference between HDMI and HDMI Ethernet is the use of an additional 2 pins that are twisted and shielded in the HDMI Ethernet version.

In the new HDMI 2.1 version, the benefit of a shield twisted pair for Ethernet is built into the spec. to eliminate interference. In addition, the ARC can be enhanced; Instead of passing approximately 1 Mbps (it was intended to be 384 Kbps but that can be stretched to 1 Mbps) it now can deliver a 38 Mbps ARC (8 channels, 192 kHz, 24 bits). That covers everything requiring a high bit rate now including – uncompressed Dolby True HD, Dolby Atmos, DTS:X, DTS HD Master Audio and so on.

Most of the disconnects that once plagued ARC should be eliminated in eARC, HDMI developers said. Now, for example, next-generation Ultra HD Blu-ray players will be able to send a full signal into the TV and the TV will be able to send back a signal with high-bit rate audio.

That audio over the 2-pin link in HDMI 2.1 also includes a “discover mechanism.” Today ARC performs discovery in CEC, which has famously suffered from brand-to-brand interoperability issues. Over the years, the HDMI Forum has received numerous complaints about CEC due to this. The issue is related to a very low-speed BUS (around 1Kbps) in CEC. When using many different HDMI-CEC devices, or even one rogue device, the BUS can become plugged and stops ARC from working. Experts said this should go away in HDMI 2.1 through the new eARC spec.

4K UHD and HDTVs

Amazon’s Camera, Photo & Video Deals

Amazon Fire TV 4K Ultra HD Set-Top Media Adapter with Alexa

Amazon Fire TV Stick with Alexa Voice Remote

Amazon Echo Voice Controlled Wireless Speaker and Home System Interface

Amazon Echo Dot Voice Controlled Home System Interface

Panasonic  Deals

Best Selling Soundbars and 5.1 Surround Systems

Best Selling Blu-ray Players

The link also builds in and sends a lip-synch correction signal because when stereo PCM is used it has zero latency, but when compressed signals are used there is higher latency in the audio requiring a synch mechanism to the video.

Here are some additional questions we had the HDMI experts answer for us:

How many different types of HDMI 2.1 cables does this specification cover?

HDMI 2.1 defines one type of cable – an HDMI 48 Gbps high-speed cable. Companies including Microsoft and Apple are said to have insisted on it. How long it is, what it’s made out of, what is inside of it [as in the case of chips for amplified cables] doesn’t matter. The cable must support Ethernet channel and must support high-speed five. If it’s spec. compliant, the specs don’t certify that it’s made out of copper, it simply specifies the electrical characteristics present.

Will this require a new connector?

The short answer is: not really. HDMI 2.1 uses the same size and shape of the primary connector used now, but it is possible to reach the specified requirements. The manufacturer will need to buy something different to put into the product to support it, but to the consumer it will be the same connector. This is crucial, since there are more than 7 billion devices in the market with this connector today. Maintaining backward compatibility with all of those legacy products and specifications is critical to HDMI Forum members.

How will the new HDMI 2.1 cable be different from what we have today?

It will look just like an HDMI cable, but to achieve the 12 Gbps performance, the length is going to suffer. With an HDMI 2.0 cable it’s difficult to go beyond 7 meters. With an HDMI 2.1 cable, lengths will shorten, although we don’t know by exactly how much yet. Still, one source told us, that shouldn’t be a big problem due to the availability of active cables that will enable longer runs. Active cables have built-in electronics to amplify the signal for longer cable runs, and typically these cables require a power supply. These cables use active electronics to help push the signal farther than typical passive cables. They are more expense, but because the need for active cables is expected to be greater with HDMI 2.1 than it was for HDMI 2.0, production volume will increase, which will cause prices to eventually drop. Meanwhile, the chip used in today’s active HDMI cables will need to change to support HDMI 2.1, since it will be twice as fast and will have four lanes, instead of three.

Regarding cable lengths, approximately 95 to 98 percent of the HDMI cables sold today are 2 to 3 meters, meaning almost everybody has a 6- to 9 -foot cable in their home. But when longer cables are needed, the aforementioned active cables will be there to address the need. Right now, active cables are a niche portion of the market – somewhere around 1 percent. In the near future, they will become more popular, more available and less pricey. Once available, make sure to get an HDMI 2.1 version active cable for future compatibility requirements when longer runs are necessary.

Improvements For Gaming

Another feature that was announced for HDMI 2.1 was improved game modes. There are three of them addressed in the spec. The first one brings a small improvement on the game mode feature today, but more importantly, requires compliance testing. With the old game mode there was no testing, which was said to have drawn complaints from a number of distrusting video game companies.

The second one allows the link to run in a high refresh rate mode. So, for example, if the TV is running in a 120 Hz mode, the game might run at 60 fps but will transmit the frame in half the time so that latency goes down. So, the speed of 60 fps is 16.7 milliseconds per frame but it is transmitted in 8 mspf.

The third step is the full variable refresh rate (or dynamic refresh rate), where the refresh rate can change. That is a big deal in gaming, and has been available for PC gaming with DisplayPort. NVIDIA and AMD have each offered their own solutions for this. These monitors are sold to hardcore gamers looking for more fluid motion. The lack of that fluid motion results from the use of a rendering engine that spits out polygons. But if the camera moves you can see in complex changes that the time it takes to render a frame varies. In video, you have to send a refresh signal every 16.7 milliseconds.

By varying the refresh rate, usually to around 60 fps, the display will buffer as necessary, the motion becomes more fluid and the rendering improves.

Will HDMI 2.1 Bring More Stringent Compliance Testing?

The biggest shortcoming of the various HDMI versions in the market today has been the failure of some manufacturers to adequately ensure their products are tested to and fully comply with specifications for each version of HDMI. A lot of effort goes into building compatible products. The HDMI administrators work with a number of test houses including Teledyne LeCroy, Simplay Labs and others to develop the Compliance Test Specification (CTS) that takes into account all of the “Shalls” addressed in the legal agreement to use any version of an HDMI spec. and to ensure new products are adequately tested and perform properly. The “Shoulds” in the agreement, of which there are many, are not tested.

Companies are still allowed to self-certify, and if their product fails to comply with the specification (not just the CTS), the company is in violation of the agreement to use the HDMI license. Still, the industry lacks an enforcement mechanism to pull a product off the shelf because it failed at some level of compliance with a standard. Therefore, the HDMI 2.1 specification will still make it necessary for consumers to act prudently when buying HDMI 2.1-enabled products, and to seek out high-quality products from reliable brands and manufacturers with solid reputations for good customer support.

HDMI executives told HD Guru that particularly with HDMI cables, products are supposed to be certified and licensed but a high degree of piracy remains.

Will HDCP 2.2 Be Sufficient To Protect Content On HDMI 2.1?

HDCP 2.2 is very robust and is based on the same technology that IPSec and most high security systems are. The RSA Keys that protect AES 128-bit encryption are said to be very robust and HDMI technology manufacturers tell us they go to extensive lengths to ensure that silicone chips that supply protection systems are not distributed to rogue companies that could use them to hack HDCP.

Is there any form of workaround available to bring compatibility with current or older AV receivers and other HDMI 2.0a components?

The use of Enhanced Audio Return Channel (or eARC) will eliminate the need for HDMI 2.1 to pass the signal through an audio component. Once the first HDMI 2.1 TVs and audio devices come out, if the link speed goes up or there is some format the audio device can’t support, the HDMI 2.1 input cable can be attached to the TV, which is equipped to accept it, and the eARC connection returns all of the supporting audio formats at the highest bit rates that the receiver or amplifier is able to support. There is no need to attach a Blu-ray player to the amplifier because the signal input gets connected to the HDMI 2.1 TV and the eARC output on the TV streams the audio out to the receiver or other audio component while turning the volume off on the TV. With eARC: 1) the audio bit rate goes all the way up to 38 Mbps; 2) the discovery mechanism in the eARC connection uses a 2-pin signal that is much more robust and reliable so that it works every time among different brands of products; and 3) it has required lip-synch built-in so pictures always match to sound.

Using a 4K/60 Hz signal, what is the maximum bit-depth, and chroma subsampling level available in HDMI 2.1?

In HDMI 2.0: 4K/60 Hz 4:4:4 chroma subsampling is possible at 8-bit or 4:2:2 in 8-, 10-, 12-bit. Maximum color bit depth at 4K is 48 bits.

In HDMI 2.1: 4K/120 Hz (4096×2160) allows for chroma subsampling of 4:4:4; 8K/60 Hz (7680×4320) 4:4:4; and 8K/120 Hz (7680×4320) 4:2:0. Maximum color bit depth at 8K is 48 bits.

Will there be a Plug Fest for HDMI 2.1?


When will we see the first HDMI 2.1 supporting devices come out?

Manufacturers are not expected to announce products until the spec. is considered final because it’s difficult to announce a product before all of the details have been determined. A logical guess would be the first device might come out in 2018, and we might see a manufacturer introducing a product like an HDMI 2.1 cable before the end of 2017.


By Greg Tarr


Have a question for the HD Guru? HD GURU|Email

Copyright ©2017 HD Guru Inc. All rights reserved. HD GURU is a registered trademark.