HDMI (High-Definition Multimedia Interface) is a proprietary compact audio/video interface for transmitting uncompressed digital data.[1] It is a digital alternative to consumer analog standards, such as radio frequency (RF) coaxial cable, composite video, S-Video, SCART, component video, D-Terminal, or VGA. HDMI connects digital audio/video sources (such as set-top boxes, DVD players, HD DVD players, Blu-ray Disc players, AVCHDcamcorders, personal computers (PCs), video game consoles such as the PlayStation 3, Xbox 360 and Wii U, AV receivers, and even some cell phones) to compatible digital audio devices, computer monitors, video projectors, tablet computers, and digital televisions.[1]
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.[2][3] HDMI supports, on a single cable, any uncompressed TV or PC video format, including standard, enhanced, high definition and 3D video signals; up to 8 channels of compressed or uncompressed digital audio; a Consumer Electronics Control (CEC) connection; and an Ethernet data connection.
The CEC allows HDMI devices to control each other when necessary and allows the user to operate multiple devices with one remote control handset.[4] Because HDMI is electrically compatible with the CEA-861 signals used by 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.[5] As an uncompressed CEA-861 connection, HDMI is independent of the various digital television standards used by individual devices, such as ATSC and DVB, as these are encapsulations of compressedMPEG video streams (which can be decoded and output as an uncompressed video stream on HDMI).
|
HDMI official logo and standard connector
|
|
Type
|
Digital audio/video connector
|
|
Production history
|
|
Designer
|
HDMI Founders (seven companies)
|
|
Designed
|
December 2002
|
|
Manufacturer
|
HDMI Adopters (over 850 companies)
|
|
Produced
|
2003–present
|
|
General specifications
|
|
Width
|
Type A (13.9 mm), Type C (10.42 mm)
|
|
Height
|
Type A (4.45 mm), Type C (2.42 mm)
|
|
Hot pluggable
|
Yes
|
|
External
|
Yes
|
|
Audio signal
|
LPCM, Dolby Digital, DTS, DVD-Audio, Super Audio CD, Dolby Digital Plus, Dolby TrueHD, DTS-HD High Resolution Audio, DTS-HD Master Audio, MPCM, DSD, DST
|
|
Video signal
|
480i, 480p, 576i, 576p, 720p, 1080i, 1080p, 1440p, 1600p, 2160p, etc.
|
|
Pins
|
19
|
|
Data
|
|
Data signal
|
Yes
|
|
Bitrate
|
10.2 Gbit/s (340 MHz)
|
|
Protocol
|
|
The HDMI specification defines the protocols, signals, electrical interfaces and mechanical requirements of the standard.[40] The maximum pixel clock rate for HDMI 1.0 was 165 MHz, which was sufficient for supporting 1080p and WUXGA (1920×1200) at 60 Hz. HDMI 1.3 increased that to 340 MHz, which allows for higher resolution (such as WQXGA, 2560×1600) across a single digital link.[41] An HDMI connection can either be single-link (type A/C) or dual-link (type B) and can have a video pixel rate of 25 MHz to 340 MHz (for a single-link connection) or 25 MHz to 680 MHz (for a dual-link connection). Video formats with rates below 25 MHz (e.g., 13.5 MHz for 480i/NTSC) are transmitted using a pixel-repetition scheme.[1]
Audio/video
To ensure baseline interoperability between different HDMI-sources and displays (as well as backward compatibility with the electrically compatible DVI standard), all HDMI compliant devices are required to support sRGB video 4:4:4, at 8 bits per component. Support for YCbCr color-space and higher color-depths ("deep color") are optional. HDMI permits xvYCC4:4:4 (8–16 bits per component), YCbCr 4:4:4 (8–16 bits per component), or YCbCr 4:2:2 (8–12 bits per component).[43][44] The color spaces that can be used by HDMI are ITU-R BT.601, ITU-R BT.709-5 and IEC 61966-2-4.[43]
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 8 channels of uncompressed audio at sample sizes of 16-bit, 20-bit and 24-bit, with sample rates of 32 kHz, 44.1 kHz, 48 kHz, 88.2 kHz, 96 kHz, 176.4 kHz and 192 kHz.[21][45] HDMI also supports any IEC 61937-compliant compressed audio stream, such as Dolby Digital and DTS, and up to 8 channels of one-bit DSD audio (used on Super Audio CDs) at rates up to four times that of Super Audio CD.[45] With version 1.3, HDMI supports lossless compressed audio streams Dolby TrueHD and DTS-HD Master Audio.[45] As with the YCbCr video, device support for audio is optional.
The HDMI standard was not designed to include passing closed caption data (for example, subtitles) to the television for decoding.[46] As such, any closed caption stream has to 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 sending an upscaled 720p/1080i format via HDMI to an HDTV has no method to pass Closed Captioning data so that the HDTV can decode as there is no line 21 VBI in that format.
Connectors
HDMI type A receptacle connector
HDMI type A plug connector
There are five HDMI connector types. Type A/B are defined in the HDMI 1.0 specification, type C is defined in the HDMI 1.3 specification, and type D/E are defined in the HDMI 1.4 specification.
Type A
Nineteen pins, with bandwidth to support all SDTV, EDTV and HDTV modes.[4] The plug (male) connector outside dimensions are 13.9 mm × 4.45 mm and the receptacle (female) connector inside dimensions are 14 mm × 4.55 mm.[47] Type A is electrically compatible with single-link DVI-D.[48]
Type B
This connector (21.2 mm × 4.45 mm) has 29 pins and can carry double the video bandwidth of type A, for use with very high-resolution future displays such as WQUXGA (3,840×2,400).[48][49] Type B is electrically compatible with dual-link DVI-D, but has not yet been used in any products.[48][50]
Type C
A Mini connector defined in the HDMI 1.3 specification, it is intended for portable devices.[1][51][52] It is smaller than the type A plug connector (10.42 mm × 2.42 mm) but has the same 19-pin configuration.[51][53] The differences are that all positive signals of the differential pairs are swapped with their corresponding shield, the DDC/CEC Ground is assigned to pin 13 instead of pin 17, the CEC is assigned to pin 14 instead of pin 13, and the reserved pin is 17 instead of pin 14.[54] The type C Mini connector can be connected to a type A connector using a type A-to-type C cable.[51][52]
Type D
A Micro connector defined in the HDMI 1.4 specification[52][55] keeps the standard 19 pins of types A and C but shrinks the connector size to something resembling a micro-USB connector.[56] The type D connector is 2.8 mm × 6.4 mm, whereas the type C connector is 2.42 mm × 10.42 mm;[57] for comparison, a micro-USB connector is 2.94 mm × 7.8 mm and USB Type A is 11.5 mm × 4.5 mm.
Type E
Automotive Connection System defined in HDMI 1.4 specification.
Cables
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.[58] 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).[55][59][60] Category 1 HDMI cables are to be marketed as "Standard" and Category 2 HDMI cables as "High Speed".[1] This labeling guideline for HDMI cables went into effect on October 17, 2008.[61][62] 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.[59] A cable of about 5 meters (16 ft) can be manufactured to Category 1 specifications easily and inexpensively by using 28 AWG (0.081 mm²) conductors.[58] With better quality construction and materials, including 24 AWG (0.205 mm²) conductors, a HDMI cable can reach lengths of up to 15 meters (49 ft).[58] 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.[63]
As of the HDMI 1.4 specification, there are the following cable types defined for HDMI in general:[64][65]
· Standard HDMI Cable with Ethernet
· Automotive HDMI Cable
· High Speed HDMI Cable with Ethernet
Cable manufacturers are officially prohibited from marketing the cables by HDMI standard version (for instance "HDMI 1.4 cable"); the cables are distinguished by bitrate support only.
Extenders
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.[66][67][68] 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.[69][70] 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 ft).[66] HDMI extenders that are based on dual Category 5/Category 6 cable can extend HDMI to 250 meters (820 ft), while HDMI extenders based on optical fiber can extend HDMI to 300 meters (980 ft).[67][68]
Communication channel protocols
HDMI has three physically separate communication channels, which are the DDC, TMDS and the optional CEC.[71]
DDC
The Display Data Channel (DDC) is a communication channel based on the I²C bus specification.[72][73] 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.[71][72][73] HDMI requires that the E-DDC support I²C standard mode speed (100 kbit/s) and allows optional support for fast mode speed (400 kbit/s).[74]
TMDS
Transition Minimized Differential Signaling (TMDS) on HDMI carries video, audio and auxiliary data via one of three modes, called the Video Data Period, the Data Island Period and the Control Period.[75] During the Video Data Period, the pixels of an active video line are transmitted.[75] 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.[75] The Control Period occurs between Video and Data Island periods.[75]
Both HDMI and DVI use TMDS to send 10-bit characters that are encoded using 8b/10b encoding for the Video Data Period and 2b/10b encoding for the Control Period. HDMI adds the ability to send audio and auxiliary data using 4b/10b encoding for the Data Island Period.[75] Each Data Island Period is 32 pixels in size and contains a 32-bit Packet Header, which includes 8 bits of BCH ECC parity data for error correction and describes the contents of the packet.[76] Each Packet contains four subpackets, and each subpacket is 64 bits in size, including 8 bits of BCH ECC parity data, allowing for each Packet to carry up to 224 bits of audio data.[77] Each Data Island Period can contain up to 18 Packets.[78] Seven of the 15 Packet types described in the HDMI 1.3a specifications deal with audio data, while the other 8 types deal with auxiliary data.[76] 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).[79][80] The Gamut Metadata Packet carries information on the color space being used for the current video stream and is required for xvYCC.[43][81][82]
CEC
Consumer Electronics Control (CEC) is a feature designed to allow the user to command and control two or more CEC-enabled boxes, that are connected through HDMI, by using only one of their remote controls. (e.g. 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.[83]
It is a one-wire bidirectional serial bus that uses the industry-standard AV.link protocol to perform remote control functions. CEC wiring is mandatory, although implementation of CEC in a product is optional.[71] It was defined in HDMI Specification 1.0 and updated in HDMI 1.2, HDMI 1.2a and HDMI 1.3a (which added timer and audio commands to the bus).[83][84][85][86]
The following is a list of HDMI-CEC commands:
· One Touch Play: the device will become active source when playback starts
· System Standby: switches all connected devices to standby
· Preset Transfer: transfers the tuner channel setup to another TV set
· One Touch Record: start recording immediately
· Timer Programming: allow one device (e.g. a TV set) to set the timer programming of another (e.g. a DVD-recorder)
· System Information: checks all components for bus addresses and configuration
· Deck Control: playback control
· Tuner Control: control the tuner of another device
· OSD Display: use the OSD of the TV set to display text
· Device Menu Control: use the menus of another device
· Routing Control: control the switching of signal sources
· Remote Control Pass Through: pass through remote control commands
· Device OSD Name Transfer: transfer the preferred device names to the TV set
|
HDMI version
|
1.0
|
1.1
|
1.2
1.2a
|
1.3
|
1.3a
1.3b
1.3b1
1.3c
|
1.4
1.4a
|
|
|
|
Yes
|
|
|
|
Yes
|
8 channel LPCM, 192 kHz, 24 bit audio capability
|
Yes
|
Yes
|
Yes
|
Yes
|
Yes
|
Yes
|
|
|
Yes
|
Yes
|
Yes
|
Yes
|
Yes
|
Yes
|
Consumer Electronic Control (CEC)[G]
|
Yes
|
Yes
|
Yes
|
Yes
|
Yes
|
Yes
|
|
|
No
|
Yes
|
Yes
|
Yes
|
Yes
|
Yes
|
|
|
No
|
No
|
Yes
|
Yes
|
Yes
|
Yes
|
|
|
|
No
|
|
|
|
No
|
|
|
No
|
No
|
No
|
Yes
|
Yes
|
Yes
|
|
|
No
|
No
|
No
|
Yes
|
Yes
|
Yes
|
|
|
No
|
No
|
No
|
Yes
|
Yes
|
Yes
|
Updated list of CEC commands[I]
|
No
|
No
|
No
|
Yes
|
Yes
|
Yes
|
|
|
No
|
No
|
No
|
No
|
No
|
Yes
|
|
Ethernet channel
|
No
|
No
|
No
|
No
|
No
|
Yes
|
|
Audio return channel (ARC)
|
No
|
No
|
No
|
No
|
No
|
Yes
|
4K × 2K resolution support[117]
|
No
|
No
|
No
|
No
|
No
|
Yes
|
Applications
Mobile Phones
Specifications
 
|
