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The High-Definition Multimedia Interface (HDMI) is an all-digital audio/video interface capable of transmitting uncompressed streams. HDMI is compatible with High-bandwidth Digital Content Protection (HDCP) Digital Rights Management technology. HDMI provides an interface between any compatible digital audio/video source, such as a set-top box, a DVD player, a PC, a video game console, or an AV receiver and a compatible digital audio and/or video monitor, such as a digital television (DTV). In 2006, HDMI began to appear as a feature on prosumer, HDTV camcorders and even high-end digital still cameras.[1][2][3]
General notesHDMI supports any TV or PC video format, including standard, enhanced, or high-definition video, plus multi-channel digital audio on a single cable. It is independent of the various DTV standards such as ATSC, and DVB (-T,-S,-C), as these are encapsulations of the MPEG movie data streams, which are passed off to a decoder, and output as uncompressed video data on HDMI. HDMI encodes the video data into TMDS for transmission digitally over HDMI. Devices are manufactured to adhere to various versions of the specification, where each version is given a number, such as 1.0 or 1.3. Each concurrent version of the specification uses the same cables, but increases the throughput and/or capabilities of what can be transmitted over the cable. For example, previously, the maximum pixel clock rate of the interface was 165MHz, sufficient for supporting 1080p at 60Hz or WUXGA (1920x1200), but HDMI 1.3 increased that to 340MHz, providing support beyond the highest resolution of computer monitors available today. See the Versions section for details. HDMI also includes support for 8-channel uncompressed digital audio at 192kHz sample rate with 24 bits/sample as well as any compressed stream such as Dolby Digital, or DTS. HDMI supports up to 8 channels of one-bit audio, such as that used on Super Audio CDs at rates up to 4x that used by SuperAudio CD. With version 1.3, HDMI now also supports very high bitrate lossless compressed streams such as Dolby TrueHD and DTS-HD Master Audio.
The HDMI Founders include consumer electronics manufacturers Hitachi, Matsushita Electric Industrial (Panasonic/National/Quasar), Philips, Sony, Thomson (RCA), Toshiba, and Silicon Image. Digital Content Protection, LLC (a subsidiary of Intel) is providing HDCP for HDMI. In addition, HDMI has the support of major motion picture producers Fox, Universal, Warner Bros., and Disney, and system operators DirecTV and EchoStar (Dish Network) as well as CableLabs and Samsung. SpecificationsHDMI defines the protocol and electrical specifications for the signaling, as well as the pin-out, electrical and mechanical requirements of the cable and connectors. ConnectorsThe HDMI Specification has expanded to include three connectors, each intended for different markets. The standard Type A HDMI connector has 19 pins, with bandwidth to support all SDTV, EDTV and HDTV modes and more. The plug outside dimensions are 13.9mm wide by 4.45mm high. Type A is electrically compatible with single-link DVI-I. A higher resolution version called Type B is defined in HDMI 1.0. Type B has 29 pins (21.2mm wide), allowing it to carry an expanded video channel for use with very high-resolution future displays, such as WQSXGA (3200x2048). Type B is electrically compatible with dual-link DVI-I, but is not in general use. The Type C mini-connector is intended for portable devices. It is smaller than Type A (10.42mm by 2.42mm) but has the same 19-pin configuration. CableEach channel in HDMI can be purposed to carry audio, video, multimedia, or device-controlling signals, or a combination of these signals. Adaptor cables - from Type A to Type C - are available. TMDS channelThe Transition Minimized Differential Signaling (TMDS) channel:
Consumer Electronics Control channelThe Consumer Electronics Control (CEC) channel is optional to implement, but wiring is mandatory. The channel:
This feature is used in two ways:
An example of the latter is to allow the DVD player, when the drawer closes with a disk, to command the TV and the intervening A/V Receiver (all with CEC) to power-up, select the appropriate HDMI ports, and auto-negotiate the proper video mode and audio mode. No remote control command is needed. Similarly, this *type* of equipment can be programmed to return to sleep mode when the movie ends, perhaps by checking the real-time clock. If it is later than 11:00pm, and the user does not specifically command the systems with the remote control, then the systems all turn off at the command from the DVD player. Content protection
VersionsDevices are manufactured to adhere to various versions of the specification, where each version is given a revision number. Each concurrent version of the specification uses the same cables, but increases the throughput and capabilities of what can be transmitted over that cable. The need for a new HDMI cable if you already have one really depends on the cable (which also has a HDMI rating). The main thing to consider is if any current cable would be able to handle the increased bandwidth - for example (10.2GBPS) that comes with version 1.3. Cable compliance testing is included in the HDMI Compliance Test Specification (see TESTID 5-3), with "Category 1" and "Category 2" defined in the HDMI Specification 1.3a (Section 4.2.6). It should further be noted that a product listed as having an HDMI version does not necessarily mean that it will have all of the features listed under the version classification, indeed some of the features are optional. For example in HDMI v1.3 it is optional to support the xvYCC wide colour standard. This means if you have bought a camcorder that supports the wide colour space (which for example is branded by Sony as "x.v.Color") you have to specifically check that the display supports both HDMI v.3 and the xvYCC wide colour standard. HDMI 1.0Released December 2002.
HDMI 1.1Released May 2004.
HDMI 1.2Released August 2005.
HDMI 1.2aReleased December 2005.
HDMI 1.3
HDMI 1.3aReleased 10 November 2006.[11]
Cable lengthThe HDMI specification does not define a maximum cable length. As with all cables, signal attenuation becomes too high at a certain length. Instead, HDMI specifies a minimum performance standard. Any cable meeting that specification is compliant. Different construction quality and materials will enable cables of different lengths. In addition, higher performance requirements must be met to support video formats with higher resolutions and/or frame rates than the standard HDTV formats. The signal attenuation and intersymbol interference caused by the cables can be compensated by using Adaptive Equalization. HDMI 1.3 defined two categories of cables: Category 1 (standard or HDTV) and Category 2 (high-speed or greater than HDTV) to reduce the confusion about which cables support which video formats. Using 28 AWG, a cable of about 5 metres (~16 feet) can be manufactured easily and inexpensively to Category 1 specifications. Higher-quality construction (24 AWG, tighter construction tolerances, etc.) can reach lengths of 12 to 15 metres (~39 to 49 feet). In addition, active cables (fiber optic or dual Cat-5 cables instead of standard copper) can be used to extend HDMI to 100 metres or more. Some companies also offer amplifiers, equalizers and repeaters that can string several standard (non-active) HDMI cables together. HDMI and high-definition optical media playersIn 2006, two competing high definition optical disc formats were released: Blu-ray Disc and HD DVD. These formats support higher-fidelity audio than the DVD format. These audio formats include Dolby Digital Plus, Dolby TrueHD and DTS-HD Master Audio. Not all of these are mandated by the Blu-ray Disc and HD DVD formats. High definition players provide a number of ways to transmit this audio. Currently, the best fidelity is available when the player is set to output LPCM over HDMI when using one of the higher fidelity formats. This requires a preprocessor or audio/video receiver capable of handling multi-channel LPCM over HDMI. While this has been allowed by the HDMI spec since 1.0, not all devices supporting HDMI 1.1 support this feature. In the future, it is likely that most devices claiming HDMI 1.1 as a feature will support at least 5.1 LPCM over HDMI. HDMI 1.3 provides for sending TrueHD and DTS-HD as bitstreams rather than LPCM. This would allow a preprocessor or audio/video receiver with the necessary decoder to decode the data itself. However the players would have to forgo mixing of interactive audio before sending it over HDMI. CriticismHDMI has been criticized for implementing part of a growing DRM process in home audio/video. See, for instance: See alsoReferences and Notes
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