The HDMI Forum formally announced Tuesday the long-awaited release of Version 2.1 of the HDMI Specification that will be offered for use by all licensed manufacturers of next-generation HDMI devices.

The specification gives chip and device manufacturers guidance in how to proceed with the implementation of HDMI 2.1 connectors in next-generation televisions, AV receivers, Ultra HD Blu-ray players, satellite and cable set-top boxes, gaming consoles and other devices, to bring the next stages of advanced AV entertainment and communication to the home. Some cable manufacturers contacted by HD Guru said they were preparing to unveil some of the first HDMI 2.1 Ultra High Speed cables at CES 2018 in January, for release at an unspecified time in 2018.

The HDMI Forum said the HDMI 2.1 Compliance Test Specification (CTS) will be published in stages through the third quarter of 2018, and HDMI adopters will be notified when it is available.

First announced at CES 2017 in January, the new connector brings a host of new and improved capabilities to the HDMI digital connector interface that has been the defacto standard for consumer digital television and video equipment for more than a decade. The HDMI plug will be virtually identical in size and shape to current HDMI 2.0) connectors, but the supporting electronics and pin configurations will change. However, the new cables will be backward compatible to support signals from devices with legacy HDMI versions.

HDMI 2.1 calls for tripling the bandwidth of the current HDMI 2.0 to 48 Gbps, using four lanes. 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 1.2a compression for everything higher than 8K with 4:2:0 chroma sub sampling, and can also be applied to lower-resolution signals. It can also be used to triple the bandwidth or increase the cable lengths.

Among the biggest advantages afforded by the new interface specification is support for a wider range of higher video resolutions and refresh rates including 8K video at 60 frames per second and 4K video at up to 120 fps. The specification is also forward compatible with resolutions up to 10K (this is intended primarily for commercial and industrial applications), the HDMI Forum revealed.

Read more about the HDMI 2.1 specification release after the jump:

Of course, the new specification provides greater flexibility in supporting various high dynamic range (HDR) profiles, including new versions like Hybrid Log-Gamma, and those using dynamic HDR metadata, like Dolby Vision, HDR10+, etc., which will be able to utilize greater bandwidth and speed capability for scene-by-scene and even frame-by-frame grading and contrast improvements and on-the-fly live HDR presentations. However, some of those newer HDR formats are being adapt for support with today’s HDMI 2.0a/b interfaces in some manufacturers’ television lines.

Another huge benefit is a new and improved version of Audio Return Channel (ARC) or “enhanced ARC (eARC),” which brings a much-needed boost in bandwidth that simplifies connectivity, device compatibility, advanced audio format support with the highest audio quality possible and provides greater ease of use.

The new HDMI 2.1 version, like HDMI Ethernet cable before it, includes a shielded twisted pair for Ethernet requirements to eliminate interference. In addition, the ARC can be enhanced to pass up to 38 Mbps (8 channels, 192 kHz, 24 bits), which is a boost from the current 1 Mbps. That covers everything requiring a high bit rate including – uncompressed Dolby True HD, Dolby Atmos, DTS:X, DTS HD Master Audio and others.

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 match sound with video.

Other benefits of the HDMI 2.1 spec include:

  • Variable Refresh Rate (VRR) reduces or eliminates lag, stutter and frame tearing for more fluid and better detailed gameplay.
  • Quick Media Switching (QMS) for movies and video eliminates the delay that can result in blank screens before content is displayed.
  • Quick Frame Transport (QFT) reduces latency for smoother no-lag gaming, and real-time interactive virtual reality.
    Auto Low Latency Mode (ALLM) allows the ideal latency setting to automatically be set allowing for smooth, lag-free and uninterrupted viewing and interactivity.
  • “Enhanced refresh rate features that ensure an added level of smooth and seamless motion and transitions for gaming, movies and video,” the HDMI Forum’s statement revealed.

To support the expanded bandwidth a new HDMI 2.1 cable with 48Gbps bandwidth was developed. This new Ultra High Speed HDMI cable is said to ensure high-bandwidth dependent features are delivered including uncompressed 8K video with HDR. It features exceptionally low EMI (electro-magnetic interference) which reduces interference with nearby wireless devices. The cable is backwards compatible and can be used with the existing installed base of HDMI devices to pass legacy version signals to newer HDMI 2.1 equipment (but not vice versa), the HDMI Forum said.

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The HDMI 2.1 specification was developed by the HDMI Forum’s Technical Working Group whose members represent some of the world’s leading manufacturers of consumer electronics, personal computers, mobile devices, cables and components. In particular, sources familiar with the development of the technology said the specification was developed with the full cooperation and assistance of the major audio companies, which are typically highly competitive with each other, to ensure device compatibility regardless of brand.

So, for example, the 2-pin link in HDMI 2.1 includes a “discover mechanism” to enable devices to better communicate with each other. Today ARC performs discovery in CEC, which has suffered from brand-to-brand interoperability issues, and numerous complaints over the years to the HDMI Forum. The issue is related to a very low-speed BUS (around 1 Kbps) in CEC. When using many different HDMI-CEC devices, or even one rogue device, the BUS can become plugged and stops ARC from working. This disappears in HDMI 2.1 through the new eARC portion of the spec.

“The HDMI Forum’s mission is to develop specifications meeting market needs, growing demands for higher performance, and to enable future product opportunities,” stated Robert Blanchard of Sony Electronics, president of the HDMI Forum. The HDMI Forum currently lists 92 member companies, and is actively inviting more companies to join to help with future HDMI development efforts.

According to sources Lattice Semiconductor developed a large part of the HDMI 2.1 specification, but HDMI 2.1 was written to the requirements of the HDMI Forum, with much input from high-end audio and video companies and the forums working with various audio compression technologies.


By Greg Tarr


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