HDMI (High-Definition Multimedia Interface) is a compact audio/video interface for transferring uncompressed video data and compressed or uncompressed digital audio data from an HDMI-compliant source device, such as a display controller, to a compatible computer monitor, video projector, digital television, or digital audio device. HDMI is a digital replacement for existing analogue video standards.
HDMI implements the EIA/CEA-861 standards, which define video formats and waveforms, transport of compressed, uncompressed, and LPCM audio, auxiliary data, and implementations of the VESA EDID. CEA-861 signals carried by HDMI are electrically compatible with the CEA-861 signals used by the digital visual interface (DVI). No signal conversion is necessary, nor is there a loss of video quality when a DVI-to-HDMI adapter is used. The CEC (Consumer Electronics Control) capability allows HDMI devices to control each other when necessary and allows the user to operate multiple devices with one remote control handset.
Several versions of HDMI have been developed and deployed since initial release of the technology but all use the same cable and connector. Newer versions optionally support advanced features such as 3D, an Ethernet data connection and improved audio and video capacity, performance and resolution.
Production of consumer HDMI products started in late 2003. In Europe either DVI-HDCP or HDMI is included in the HD ready in-store labeling specification for TV sets for HDTV, formulated by EICTA with SES Astra in 2005. HDMI began to appear on consumer HDTV camcorders and digital still cameras in 2006. As of January 8, 2013 (ten years after the release of the first HDMI specification), over 3 billion HDMI devices have been sold.
Although no maximum length for an HDMI cable is specified, signal attenuation (dependent on the cable’s construction quality and conducting materials) limits usable lengths in practice. HDMI 1.3 defines two cable categories: Category 1-certified cables, which have been tested at 74.5 MHz (which would include resolutions such as 720p60 and 1080i60), and Category 2-certified cables, which have been tested at 340 MHz (which would include resolutions such as 1080p60 and 2160p30). Category 1 HDMI cables are marketed as “Standard” and Category 2 HDMI cables as “High Speed”. This labeling guideline for HDMI cables went into effect on October 17, 2008. Category 1 and 2 cables can either meet the required parameter specifications for interpair skew, far-end crosstalk, attenuation and differential impedance, or they can meet the required nonequalized/equalized eye diagram requirements. A cable of about 5 meters (16 feet) can be manufactured to Category 1 specifications easily and inexpensively by using 28 AWG (0.081 mm²) conductors. With better quality construction and materials, including 24 AWG (0.205 mm²) conductors, an HDMI cable can reach lengths of up to 15 meters (49 feet). Many HDMI cables under 5 meters of length that were made before the HDMI 1.3 specification can work as Category 2 cables, but only Category 2-tested cables are guaranteed to work for Category 2 purposes.
As of the HDMI 1.4 specification, these are the following cable types defined for HDMI in general:
- Standard HDMI Cable – up to 1080i and 720p
- Standard HDMI Cable with Ethernet
- Automotive HDMI Cable
- High Speed HDMI Cable – 1080p, 4K, 3D and deep color
- High Speed HDMI Cable with Ethernet
An HDMI cable is usually composed of four shielded twisted pairs, with impedance of the order of 100 Ω, plus several separate conductors.
An HDMI extender is a single device (or pair of devices) powered with an external power source or with the 5V DC from the HDMI source. Long cables can cause instability of HDCP and blinking on the screen, due to the weakened DDC signal that HDCP requires. HDCP DDC signals must be multiplexed with TMDS video signals to be compliant with HDCP requirements for HDMI extenders based on a single Category 5/Category 6 cable. Several companies offer amplifiers, equalizers and repeaters that can string several standard HDMI cables together. Active HDMI cables use electronics within the cable to boost the signal and allow for HDMI cables of up to 30 meters (98 feet). Tthose based on HDBaseT can extend to 100 meters, HDMI extenders that are based on dual Category 5/Category 6 cable can extend HDMI to 250 meters (820 feet), while HDMI extenders based on optical fiber can extend HDMI to 300 meters (980 feet).
HDMI devices are manufactured to adhere to various versions of the specification, in which each version is given a number and/or letter, such as 1.0, 1.2, or 1.4b. Each subsequent version of the specification uses the same kind of cable but increases the bandwidth and/or capabilities of what can be transmitted over the cable. A product listed as having an HDMI version does not necessarily mean that it will have all of the features that are listed for that version, since some HDMI features are optional, such as deep color and xvYCC (which is branded by Sony as “x.v.Color”). Note that with the release of the version 1.4 cable, the HDMI Licensing LLC group (which oversees the HDMI standard) will require that any reference to version numbers be removed from all packaging and advertising for the cable. Non-cable HDMI products starting on January 1, 2012 will no longer be allowed to reference the HDMI number and will be required to state which features of the HDMI specification the product supports.
Version 1.0 to 1.2
HDMI 1.0 was released December 9, 2002 and is a single-cable digital audio/video connector interface with a maximum TMDS bandwidth of 4.95 Gbit/s. It supports up to 3.96 Gbit/s of video bandwidth (1080p/60 Hz or UXGA) and 8 channel LPCM/192 kHz/24-bit audio. HDMI 1.1 was released on May 20, 2004 and added support for DVD-Audio. HDMI 1.2 was released August 8, 2005 and added support for One Bit Audio, used on Super Audio CDs, at up to 8 channels. It also added the availability of HDMI type A connectors for PC sources, the ability for PC sources to only support the sRGB color space while retaining the option to support the YCbCr color space, and required HDMI 1.2 and later displays to support low-voltage sources. HDMI 1.2a was released on December 14, 2005 and fully specifies Consumer Electronic Control (CEC) features, command sets and CEC compliance tests.
HDMI 1.3 was released June 22, 2006 and increased the single-link bandwidth to 340 MHz (10.2 Gbit/s). It optionally supports deep color, with 30-bit, 36-bit and 48-bit xvYCC, sRGB, or YCbCr, compared to 24-bit sRGB or YCbCr in previous HDMI versions. It also optionally supports output of Dolby TrueHD and DTS-HD Master Audio streams for external decoding by AV receivers. It incorporates automatic audio syncing (audio video sync) capability. It defined cable Categories 1 and 2, with Category 1 cable being tested up to 74.25 MHz and Category 2 being tested up to 340 MHz. It also added the new type C Mini connector for portable devices.
HDMI 1.3a was released on November 10, 2006 and had Cable and Sink modifications for type C, source termination recommendations, and removed undershoot and maximum rise/fall time limits. It also changed CEC capacitance limits, clarified sRGB video quantization range, and CEC commands for timer control were brought back in an altered form, with audio control commands added. It also added support for optionally streaming SACD in its bitstream DST format rather than uncompressed raw DSD like from HDMI 1.2 onwards.
HDMI 1.3b, 1.3b1 and 1.3c were released on March 26, 2007, November 9, 2007, and August 25, 2008 respectively. They do not introduce differences on HDMI features, functions, or performance, but only describe testing for products based on the HDMI 1.3a specification regarding HDMI compliance (1.3b), the HDMI type C Mini connector (1.3b1) and active HDMI cables (1.3c ).
HDMI 1.4 with audio return channel
HDMI 1.4 was released on May 28, 2009, and the first HDMI 1.4 products were available in the second half of 2009. HDMI 1.4 increases the maximum resolution to 4K × 2K, i.e. 3840×2160 (Ultra HD) at 24 Hz/25 Hz/30 Hz or 4096×2160 (4) at 24 Hz (which is a resolution used with digital theaters); adds an HDMI Ethernet Channel (HEC), which allows for a 100 Mbit/s Ethernet connection between the two HDMI connected devices so they can share an Internet connection; and introduces an audio return channel (ARC), 3D Over HDMI, a new Micro HDMI Connector, expanded support for color spaces, with the addition of sYCC601, Adobe RGB and Adobe YCC601; and an Automotive Connection System. HDMI 1.4 supports several stereoscopic 3D formats including field alternative (interlaced), frame packing (a full resolution top-bottom format), line alternative full, side-by-side half, side-by-side full, 2D + depth, and 2D + depth + graphics + graphics depth (WOWvx), with additional top/bottom formats added in version 1.4a. HDMI 1.4 requires that 3D displays support the frame packing 3D format at either 720p50 and 1080p24 or 720p60 and 1080p24. High Speed HDMI 1.3 cables can support all HDMI 1.4 features except for the HDMI Ethernet Channel.
HDMI 1.4a was released on March 4, 2010 and adds two additional mandatory 3D formats for broadcast content, which was deferred with HDMI 1.4 in order to see the direction of the 3D broadcast market. HDMI 1.4a has defined mandatory 3D formats for broadcast, game, and movie content. HDMI 1.4a requires that 3D displays support the frame packing 3D format at either 720p50 and 1080p24 or 720p60 and 1080p24, side-by-side horizontal at either 1080i50 or 1080i60, and top-and-bottom at either 720p50 and 1080p24 or 720p60 and 1080p24.
HDMI 1.4b was released on October 11, 2011. One of the new features is that it adds support to 3D 1080p video at 120 Hz – allowing frame packing 3D format at 1080p60 per Eye (120 Hz total). All future versions of the HDMI specification will be made by the HDMI Forum that was created on October 25, 2011.
Version 2.0 HDMI 2.0, referred to by some manufacturers as HDMI UHD, was released on September 4, 2013. HDMI 2.0 increases the maximum TMDS per channel throughput from 3.4 Gbit/s to 6 Gbit/s which allows for a maximum total TMDS throughput of 18 Gbit/s. This allows HDMI 2.0 to support 4K resolution at 60 frames per second (fps). Other features of HDMI 2.0 include support for the Rec. 2020 color space, Dual View, 4:2:0 chroma subsampling, 25 fps 3D formats, up to 32 channels of audio, up to 1536 kHz audio, up to 4 audio streams, 21:9 aspect ratio, the HE-AAC and DRA audio standards, dynamic auto lip-sync, improved 3D capability, and additional CEC functions.