HDMI (High-Definition Multimedia Interface) is a compact audio/video interface for transferring uncompressed video data and compressed or uncompressed digital audio data from a HDMI-compliant source device to a compatible computer monitor, video projector, digital television, or digital audio device HDMI is a digital replacement for existing analog video standards

HDMI implements the EIA/CEA- standards, which define video formats and waveforms, transport of compressed, uncompressed, and LPCM audio, auxiliary data, and implementations of the VESA EDID CEA- signals carried by HDMI are electrically compatible with the CEA- 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 D, an Ethernet data connection and improved audio and video capacity, performance and resolution

The HDMI Founders are Hitachi, Matsushita Electric Industrial (Panasonic/National/Quasar), Philips, Silicon Image, Sony, Thomson, RCA and Toshiba Digital Content Protection, LLC provides HDCP (which was developed by Intel) for HDMI HDMI has the support of motion picture producers Fox, Universal, Warner Bros and Disney, along with system operators DirecTV, EchoStar (Dish Network) and CableLabs

The HDMI Founders began development on HDMI  on April , with the goal of creating an AV connector that was backward-compatible with DVI At the time, DVI-HDCP (DVI with HDCP) and DVI-HDTV (DVI-HDCP using the CEA--B video standard) were being used on HDTVs HDMI  was designed to improve on DVI-HDTV by using a smaller connector and adding support for audio, and enhanced support for YCbCr and consumer electronics control functions

The first Authorized Testing Center (ATC), which tests HDMI products, was opened by Silicon Image on June , in California, United States The first ATC in Japan was opened by Panasonic on May , in Osaka The first ATC in Europe was opened by Philips on May , in Caen, France The first ATC in China was opened by Silicon Image on November , in Shenzhen The first ATC in India was opened by Philips on June , in Bangalore The HDMI website contains a list of all the ATCs

According to In-Stat, the number of HDMI devices sold was  million in ,  million in ,  million in , and  million in  HDMI has become the de facto standard for HDTVs, and according to In-Stat, around % of digital televisions in  included HDMI In-Stat has estimated that  million HDMI devices were sold in  On April ,  there were over  consumer electronics and PC companies that had adopted the HDMI specification (HDMI Adopters) On January , HDMI Licensing, LLC announced that HDMI had reached an installed base of over  million HDMI devices In-Stat has estimated that  million HDMI devices will sell in  and that all digital televisions by the end of  would have at least one HDMI input

On January , In-Stat reported that shipments of HDMI were expected to exceed those of DVI in , driven primarily by the consumer electronics market

PC Magazine awarded a Technical Excellence Award in the Home Theater category for an "innovation that has changed the world" to the CEC portion of the HDMI specification Ten companies were given a Technology and Engineering Emmy Award for their development of HDMI by the National Academy of Television Arts and Sciences on January ,

On October , the HDMI Forum was established by the HDMI Founders to create an open organization so that interested companies can participate in the development of the HDMI specification All members of the HDMI Forum have equal voting rights, may participate in the Technical Working Group, and if elected can be on the Board of Directors There is no limit to the number of companies allowed in the HDMI Forum though companies must pay an annual fee of $, with an additional annual fee of $, for those companies who serve on the Board of Directors The Board of Directors will be made up of  companies who are elected every  years by a general vote of HDMI Forum members All future development of the HDMI specification will take place in the HDMI Forum and will be built upon the HDMI b specification Also on the same day HDMI Licensing, LLC announced that there were over , HDMI Adopters and that over  billion HDMI-enabled products had shipped since the launch of the HDMI standard From October , all development of the HDMI specification became the responsibility of the newly created HDMI Forum

On January , HDMI Licensing, LLC announced that that there were over , HDMI Adopters and that over  billion HDMI devices had shipped since the launch of the HDMI standard The day also marked the -year anniversary of the release of the first HDMI specification

The HDMI specification defines the protocols, signals, electrical interfaces and mechanical requirements of the standard The maximum pixel clock rate for HDMI  was  MHz, which was sufficient to support p and WUXGA (×) at  Hz HDMI  increased that to  MHz, which allows for higher resolution (such as WQXGA, ×) across a single digital link An HDMI connection can either be single-link (type A/C) or dual-link (type B) and can have a video pixel rate of  MHz to  MHz (for a single-link connection) or  MHz to  MHz (for a dual-link connection) Video formats with rates below  MHz (eg,  MHz for i/NTSC) are transmitted using a pixel-repetition scheme
Audio/video

HDMI uses the Consumer Electronics Association/Electronic Industries Alliance  standards HDMI  to HDMI a uses the EIA/CEA--B video standard, HDMI  uses the CEA--D video standard, and HDMI  uses the CEA--E video standard The CEA--E document defines "video formats and waveforms; colorimetry and quantization; transport of compressed and uncompressed, as well as Linear Pulse Code Modulation (LPCM), audio; carriage of auxiliary data; and implementations of the Video Electronics Standards Association (VESA) Enhanced Extended Display Identification Data Standard (E-EDID)" On July , the CEA announced the publication of CEA--F which is a standard that can be used by interfaces such as DVI, HDMI, and LVDS CEA--F adds support for several Ultra HD video formats and additional color spaces

To ensure baseline compatibility between different HDMI sources and displays (as well as backward compatibility with the electrically compatible DVI standard) all HDMI devices must support the sRGB color space at  bits per component Support for the YCbCr color space and higher color depths ("deep color") is optional HDMI permits sRGB :: chroma subsampling (– bits per component), xvYCC :: chroma subsampling (– bits per component), YCbCr :: chroma subsampling (– bits per component), or YCbCr :: chroma subsampling (– bits per component) The color spaces that can be used by HDMI are ITU-R BT, ITU-R BT- and IEC --

For digital audio, if an HDMI device supports audio, it is required to support the baseline format: stereo (uncompressed) PCM Other formats are optional, with HDMI allowing up to  channels of uncompressed audio at sample sizes of -bit, -bit and -bit, with sample rates of  kHz,  kHz,  kHz,  kHz,  kHz,  kHz and  kHz HDMI also supports any IEC -compliant compressed audio stream, such as Dolby Digital and DTS, and up to  channels of one-bit DSD audio (used on Super Audio CDs) at rates up to four times that of Super Audio CD With version , HDMI supports lossless compressed audio streams Dolby TrueHD and DTS-HD Master Audio As with the YCbCr video, device support for audio is optional Audio Return Channel (ARC) is a feature introduced in the HDMI  standard "Return" refers to the case where the audio comes from the TV and can be sent "upstream" to the AV receiver using the HDMI cable connected to the AV receiver An example given on the HDMI website is that a TV that directly receives a terrestrial/satellite broadcast, or has a video source built in, sends the audio "upstream" to the AV receiver

The HDMI standard was not designed to pass closed caption data (for example, subtitles) to the television for decoding As such, any closed caption stream must be decoded and included as an image in the video stream(s) prior to transmission over an HDMI cable to be viewed on the DTV This limits the caption style (even for digital captions) to only that decoded at the source prior to HDMI transmission This also prevents closed captions when transmission over HDMI is required for upconversion For example, a DVD player that sends an upscaled p/i format via HDMI to an HDTV has no way to pass Closed Captioning data so that the HDTV can decode it, as there is no line  VBI in that format
Uncompressed video

The HDMI specification specifies several modes of uncompressed digital video Although often HD video capable cameras include an HDMI interface for playback or even live preview, the image processor and the video processor of cameras usable for uncompressed video must be able to deliver the full image resolution at the specified frame rate in realtime without any missing frames causing judder Therefore usable uncompressed video out of HDMI is often called "Clean HDMI"
Communication channel protocols

HDMI has three physically separate communication channels, which are the DDC, TMDS and the optional CEC HDMI  added ARC and HEC
DDC

The Display Data Channel (DDC) is a communication channel based on the I²C bus specification HDMI specifically requires support for the Enhanced Display Data Channel (E-DDC), which is used by the HDMI source device to read the E-EDID data from the HDMI sink device to learn what audio/video formats it supports HDMI requires that the E-DDC support I²C standard mode speed ( kbit/s) and allows optional support for fast mode speed ( kbit/s)

The DDC channel is actively used for High-bandwidth Digital Content Protection
TMDS

Transition Minimized Differential Signaling (TMDS) on HDMI interleaves video, audio and auxiliary data using three different packet types, called the Video Data Period, the Data Island Period and the Control Period During the Video Data Period, the pixels of an active video line are transmitted During the Data Island period (which occurs during the horizontal and vertical blanking intervals), audio and auxiliary data are transmitted within a series of packets The Control Period occurs between Video and Data Island periods

Both HDMI and DVI use TMDS to send -bit characters that are encoded using b/b encoding that differs from the original IBM form for the Video Data Period and b/b encoding for the Control Period HDMI adds the ability to send audio and auxiliary data using b/b encoding for the Data Island Period Each Data Island Period is  pixels in size and contains a -bit Packet Header, which includes  bits of BCH ECC parity data for error correction and describes the contents of the packet Each Packet contains four subpackets, and each subpacket is  bits in size, including  bits of BCH ECC parity data, allowing for each Packet to carry up to  bits of audio data Each Data Island Period can contain up to  Packets Seven of the  Packet types described in the HDMI a specifications deal with audio data, while the other  types deal with auxiliary data Among these are the General Control Packet and the Gamut Metadata Packet The General Control Packet carries information on AVMUTE (which mutes the audio during changes that may cause audio noise) and Color Depth (which sends the bit depth of the current video stream and is required for deep color) The Gamut Metadata Packet carries information on the color space being used for the current video stream and is required for xvYCC
CEC

Consumer Electronics Control (CEC) is an HDMI feature designed to allow the user to command and control up-to  CEC-enabled devices, that are connected through HDMI, by using only one of their remote controls (for example by controlling a television set, set-top box, and DVD player using only the remote control of the TV) CEC also allows for individual CEC-enabled devices to command and control each other without user intervention

It is a one-wire bidirectional serial bus that is based on the CENELEC standard AVlink protocol to perform remote control functions CEC wiring is mandatory, although implementation of CEC in a product is optional It was defined in HDMI Specification  and updated in HDMI , HDMI a and HDMI a (which added timer and audio commands to the bus) USB to CEC adapters exist that allow a computer to control CEC-enabled devices

Trade names for CEC are Anynet+ (Samsung), Aquos Link (Sharp), BRAVIA Link and BRAVIA Sync (Sony), HDMI-CEC (Hitachi), E-link (AOC), Kuro Link (Pioneer), CE-Link and Regza Link (Toshiba), RIHD (Remote Interactive over HDMI) (Onkyo), RuncoLink (Runco International), SimpLink (LG), T-Link (ITT), HDAVI Control, EZ-Sync, VIERA Link (Panasonic), EasyLink (Philips), and NetCommand for HDMI (Mitsubishi)

The following is a list of the most commonly used HDMI-CEC commands:

    One Touch Play allows devices to switch the TV to use it as the active source when playback starts
    System Standby enables users to switch multiple devices to standby mode with the press of one button
    Preset Transfer transfers the tuner channel setup to another TV set
    One Touch Record allows users to record whatever is currently being shown on the HDTV screen on a selected recording device
    Timer Programming allows users to use the electronic program guides (EPGs) that are built into many HDTVs and set-top-boxes to program the timer in recording devices like PVRs and DVRs
    System Information checks all components for bus addresses and configuration
    Deck Control allows a component to interrogate and control the operation (play, pause, rewind etc), of a playback component (Blu-ray or HD DVD player or a Camcorder, etc)
    Tuner Control allows a component to control the tuner of another component
    OSD Display uses the OSD of the TV set to display text
    Device Menu Control allows a component to control the menu system of another component by passing through the user interface (UI) commands
    Routing Control controls the switching of signal sources
    Remote Control Pass Through allows remote control commands to be passed through to other devices within the system
    Device OSD Name Transfer transfers the preferred device names to the TV set
    System Audio Control allows the volume of an AV receiver, integrated amplifier or preamplifier to be controlled using any remote control from a suitably equipped device(s) in the system

ARC and HEC

HDMI  introduces two features called ARC (Audio Return Channel) and HEC (HDMI Ethernet Channel) These features use two pins from the connector: a previously unused pin and the hot plug detect pin

ARC is an audio link meant to replace other cables between the TV and the A/V receiver or speaker system This direction is used when the TV is the one that generates or receives the video stream instead of the other equipment A typical case is the reception of ATSC or DVB signals by a TV, but reproduction of audio is handled by the other equipment Without ARC, the audio output from the TV needs to be routed by another cable, typically TOS-Link or coax, into the speaker system

HEC provides a bidirectional Ethernet communication at  Mbit/s It also goes by the name HEAC (HDMI Ethernet Audio Control) The physical layer of the Ethernet implementation uses attenuated BASE-TX type signals on a single twisted pair for both transmit and receive
Compatibility with DVI

An adapter with a DVI receptacle connector to HDMI plug connector

An adapter with HDMI (male) and DVI (female) connectors

An adapter with an HDMI receptacle connector to DVI plug connector with a close up of the HDMI connector

An adapter with DVI and HDMI (female) connectors

HDMI is backward compatible with single-link Digital Visual Interface digital video (DVI-D or DVI-I, but not DVI-A) No signal conversion is required when an adapter or asymmetric cable is used, so there is no loss of video quality

From a user's perspective, an HDMI display can be driven by a single-link DVI-D source, since HDMI and DVI-D define an overlapping minimum set of supported resolutions and framebuffer formats to ensure a basic level of interoperability In the reverse case a DVI-D monitor would have the same level of basic interoperability unless there are content protection issues with High-bandwidth Digital Content Protection (HDCP) or the HDMI color encoding is in component color space YCbCr which is not supported by DVI, instead of RGB An HDMI source such as a Blu-ray player may demand HDCP-compliance of the display, and refuse to output HDCP-protected content to a non-compliant display A further complication is that there is a small amount of display equipment, such as some high-end home theater projectors, designed with HDMI inputs but not HDCP-compliant

Any DVI-to-HDMI adapter can function as an HDMI-to-DVI adapter (and vice-versa) Typically, the only limitation is the gender of the adapter's connectors and the gender of the cables and sockets it is used with

Features specific to HDMI, such as remote-control and audio transport, are not available in devices that use legacy DVI-D signalling However, many devices output HDMI over a DVI connector (eg ATI -series and NVIDIA GTX -series video cards), and some multimedia displays may accept HDMI (including audio) over a DVI input Exact capabilities beyond basic compatibility vary from product to product Adapters are generally bi-directional
Audio support

Since the DVI specification does not support audio transport, an interoperability problem arises when an HDMI-source drives a legacy DVI display (such as a PC monitor), or conversely, when a DVI source drives an HDMI display While HDMI and DVI compliance rules ensure that a DVI video connection can be successfully negotiated and established (via a mutually supported display mode), the audio signal must still be transported through means outside of the DVI connection Typically, an HDMI-equipped source will provide additional outputs for audio, such as line-level analog and S/PDIF, which provide a baseline audio program (such as stereo PCM) Likewise, when displaying video from an HDMI jack, an HDMI-equipped display may support alternative audio sourcing from a separate pair of analog-audio inputs Provision for any of these compatibility mechanisms is down to the manufacturer; they are not specified by HDMI By , nearly all HDMI-equipped sources (set-top and media-extender boxes, Blu-ray and DVD players, and PCs) provided separate analog audio outputs, and many HDMI-equipped televisions supported alternate-audio input when sourcing video from an HDMI input
Content protection (HDCP)

High-bandwidth Digital Content Protection (HDCP) is a newer form of Digital Rights Management Intel created the original technology to make sure that digital content followed the guidelines set by the Digital Content Protection group

HDMI can use HDCP to encrypt the signal if required by the source device CSS, CPRM and AACS require the use of HDCP on HDMI when playing back encrypted DVD Video, DVD Audio, HD DVD and Blu-ray Disc The HDCP Repeater bit controls the authentication and switching/distribution of an HDMI signal According to HDCP Specification  (beginning with HDMI CTS a), any system that implements HDCP must do so in a fully compliant manner HDCP testing that was previously only a requirement for optional tests such as the "Simplay HD" testing program is now part of the requirements for HDMI compliance HDCP allows for up to  devices to be connected, with up to  levels, using a combination of sources, sinks and repeaters A simple example of this is several HDMI devices connected to an HDMI AV receiver that is connected to an HDMI display

Devices called HDCP strippers can remove the HDCP information from the video signal so the video can play on non-HDCP-compliant displays, though a fair use and non-disclosure form must usually be signed with a registering agency before use