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HDMI (High-Definition Multimedia Interface)

By Pat Brans

What is HDMI (High-Definition Multimedia Interface)?

HDMI (High-Definition Multimedia Interface) is a proprietary specification designed to ensure compatibility between video and audio devices over a single digital interface. The specification is used for consumer electronics -- including high-definition and ultra-HD TVs, DVD and Blu-ray players, game consoles, streaming devices such as Roku, soundbars, laptops and PCs -- as well as for automotive and commercial devices. HDMI cables connect these devices and carry both uncompressed digital audio and video signals over a single cable.

HDMI specifications include physical features, or how cables and devices interface mechanically; electrical features, or how much power the cable carries; and communication protocols, or what signals are sent over cables to allow two pieces of equipment to communicate.

The first HDMI specification was released in December 2002. It was developed by Philips, Lattice Semiconductor Corp., Maxell Ltd., Panasonic Group, Sony Group Corp., Toshiba Corp. and Vantiva. The specification is licensed by HDMI Licensing Administrator Inc. (HDMI LA), the agency appointed by HDMI Forum.

The seven founders developed and released five major updates to the specification from 2002 to 2009. The 1.x specifications included the following fundamental features:

• Audio Return Channel (ARC), which sends audio from a TV to an amplifier or audio/video receiver or soundbar.
• Multichannel digital audio formats.
• Three-dimensional (3D) video.
• Auto lip-sync, which synchronizes audio and video.
• Consumer Electronics Control commands, which enable a single remote to control multiple devices.
• Deep color.

The first five releases of the HDMI specification were the following:

1. 2002. HDMI 1.0, which supported 4.95 gigabits per second (Gbps), or 1K@60, which is 1K resolution per frame, or 1920 x 1080 pixels at 60 frames per second.
2. 2004. HDMI 1.1, which added support for DVD-Audio.
3. 2005. HDMI 1.2, which added 1-bit audio for Super Audio CDs.
4. 2006. HDMI 1.3, which supported 10.2 Gbps, or 4K@30, which is 4K resolution per frame, or 3840 x 2160 at 30 frames per second.
5. 2009. HDMI 1.4, which added HDMI Ethernet Channel, ARC, 3D over HDMI, a new micro HDMI connector, an expanded set of colors and an automotive connection system (ACS).

What is HDMI Forum?

HDMI Forum Inc. is a nonprofit corporation formed by the seven companies that developed the original HDMI specification to encourage broader industry participation in the development of future versions of the HDMI specification. The forum is currently made up of more than 90 companies. This includes manufacturers of consumer electronics, PCs, mobile devices, cables, components and test equipment. It also includes movie studios, service providers and test labs.

Since its inception in October 2011, HDMI Forum has been responsible for all standardization activities, including the development and release of updates to the specification.

HDMI Forum developed and released three updates to the HDMI specification:

1. 2013. HDMI 2.0, which supported 18 Gbps (4K@60).
2. 2017. HDMI 2.1, which supported 48 Gbps (8K@60).
3. 2022. HDMI 2.1a, which added support for Source-Based Tone Mapping (SBTM).

To improve the quality of HDMI cables, the forum added the Premium HDMI Cable Certification Program in 2015 and the Ultra High-Speed HDMI Cable Certification Program in 2020.

What is included in the current version of the HDMI specification?

The HDMI 2.1a specification supports higher video resolution and refresh rates, high dynamic range (HDR) formats and bandwidth capacity of up to 48 Gbps. HDMI 2.1a is backward-compatible with early versions of HDMI.

The HDMI 2.1a specification includes a new cable, called the Ultra High-Speed HDMI Cable, which supports up to 48 Gbps bandwidth and which must be certified under the Ultra High-Speed HDMI Certification Program. The cables are tested to ensure bandwidth and protocol compliance, as well as low electromagnetic interference (EMI) with other technology that may be operating nearby, including Bluetooth, Wi-Fi, mobile phones and streaming media players.

The HDMI 2.1a specification includes the following features, some of which were introduced in 2.0 and 2.1:

• SBTM, which allows part of the HDR mapping to occur in the source device instead of just in the display device, which is useful when HDR and standard dynamic range video or graphics are combined in a single picture.
• Enhanced ARC, or eARC, which supports the most advanced and highest-quality audio formats, ensuring full compatibility between audio devices and other HDMI 2.1a products.
• Enhanced gaming features, such as variable refresh rate, auto low-latency mode and quick frame transport.
• Quality media switching, which eliminates delays that often occur when a video device changes HDMI frame rates.
• HDMI cable power to power HDMI cables directly from an HDMI connector, thereby eliminating the need for a separate power cable.

What are the types of HDMI connectors?

HDMI includes five connector types, all defined in 1.x specifications. Types A and B were defined in the HDMI 1.0 specification, type C was defined in the HDMI 1.3 specification, and types D and E were defined in the HDMI 1.4 specification:

1. Type A. The standard connector is the most widely used of the five HDMI connector types. It consists of 19 pins.
2. Type B. The dual-link connector was developed for high-resolution displays using 21 pins. It's electronically compatible with single-link Digital Visual Interface - Digital (DVI-D), but it has never been used by mainstream consumer products. The HDMI 1.3 specification exceeded the bandwidth of dual-link DVI-D, effectively rendering type B obsolete.
3. Type C. The mini connector has the same 19-pin configuration and supports the same features as the type A connector but in a smaller, more compact form factor for use on portable devices, such as cameras and tablets. Some of the signals changed with respect to type A connectors, so a special converter cable is required to connect type A connectors to type C connectors.
4. Type D. The micro connector has the same functionality as types A and C but is about half the width of the type C connector and is used in small, portable devices, such as phones. This connector uses 19 pins, but the pin assignment is different from types A and C. Type D connectors resemble micro-USB connectors.
5. Type E. The ACS for use inside vehicles has a locking tab to keep the cable in place despite vibrations and a shell to keep moisture and dirt from interfering with the signals.

HDMI LA maintains a list of approved connectors.

What are the types of HDMI cables?

HDMI cables are made up of four shielded twisted pairs and seven separate conductors. Those that support Ethernet include an additional shielded twisted pair made from three of the separate conductors.

Several HDMI cable types have been specified to meet different performance standards, along with cable certification designations. The current cable types and their performance are listed as follows from most recent to oldest. Certification designations are provided for cable specifications developed after 2015, the year the first cable certification program was launched:

• Ultra High-Speed HDMI supports up to 48 Gbps, with exceptionally low EMI. It's the only cable that supports all HDMI 2.1a features, including uncompressed digital video at 8K@60 and 4K@120. The cable packaging is required to display the Ultra High-Speed HDMI Cable Certification Label.
• Premium High-Speed HDMI and Premium High-Speed HDMI with Ethernet support up to 18 Gbps, with low EMI. These cables support advanced features, including 4K@60, HDR and expanded color spaces. The cable packaging is required to display HDMI LA's Premium HDMI Cable Certification Label.
• High-Speed HDMI with Ethernet supports up to 10.2 Gbps. This cable is the same as High-Speed HDMI except that it has an additional data channel, called HDMI Ethernet Channel, dedicated to Ethernet networking.
• High-Speed HDMI supports up to 10.2 Gbps and is designed to handle advanced display technologies, such as 4K@30, 3D and deep color. This cable is recommended for connecting a 1080p HD display to a 1080p HD content source, such as a Blu-ray Disc player.
• High-Speed Automotive HDMI is meant to connect with an automotive system and needs to send a stronger signal than other cable types. It may also use a special dust- and vibration-resistant HDMI type E connector with a locking tab.
• Standard HDMI with Ethernet is the same as Standard HDMI except that it offers an additional channel, HDMI Ethernet Channel, dedicated to Ethernet networking.
• Standard HDMI was designed to support older consumer applications and has mostly been replaced by High-Speed HDMI cables. While these cables work well with some applications, they don't support the higher resolution, refresh rates and bandwidth requirements of most of the other applications on the market.
• Standard Automotive HDMI is an older version of the High-Speed Automotive HDMI cable, with special dust- and vibration-resistant HDMI type E connectors and a locking tab, as well as a stronger signal to support the automobile environment. These cables work with some applications but don't offer the advanced performance needed by most modern applications.

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