High-Definition Multimedia Interface Totally Explained

Everything about The High-definition Multimedia Interface totally explained

The High-Definition Multimedia Interface (HDMI) is a compact audio/video connector interface for transmitting uncompressed digital streams. It represents a digital alternative to consumer analog standards such as Radio Frequency (RF) coaxial cable, composite video, S-Video, SCART, component video, D-Terminal, and VGA.
HDMI connects digital audio/video sources such as set-top boxes, Blu-ray Disc players, personal computers, video game consoles, and AV receivers to compatible digital audio devices, video monitors, and digital televisions (DTV). The world's first HDMI products started shipping in the fall of 2003 and currently over 800 CE and PC companies have adopted the HDMI specification (HDMI Adopters). HDMI began to appear on consumer HDTV camcorders and expensive digital still cameras in 2006. Shipments of HDMI are expected to exceed that of Digital Visual Interface (DVI) in 2008, driven primarily by the Consumer Electronics (CE) Market.

General notes

HDMI supports, on a single cable, any TV or PC video format including standard, enhanced, and high-definition video along with up to 8 channels of digital audio. 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 subsequent 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 165 MHz, sufficient for supporting 1080p at 60 Hz or WUXGA (1920x1200) at 60 Hz, but HDMI 1.3 increased that to 340 MHz, providing support for WQXGA (2560x1600) and beyond across a single digital link. See also: HDMI Versions.
   HDMI also includes support for 8-channel uncompressed digital audio at 192 kHz 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 Super Audio CD. With version 1.3, HDMI now also supports lossless compressed streams such as Dolby TrueHD and DTS-HD Master Audio.
   In the U.S., HDCP support is a standard feature on digital TVs while in the PC industry it's becoming more common but still often depends on the specific model. The first computer monitors with HDCP support started being released in 2005 and by February 2006 a dozen had been released.
   The HDMI Founders are Hitachi, Matsushita Electric Industrial (Panasonic/National/Quasar), Philips, Silicon Image, Sony, Thomson (RCA), and Toshiba. DVI signal is electrically compatible with HDMI video signal. No signal conversion needs to take place when an adapter is used and consequently no loss in quality occurs. Stated more technically: HDMI is backward-compatible with the single-link Digital Visual Interface carrying digital video (DVI-D or DVI-I, but not DVI-A) used on modern computer monitors and graphics cards. This means that a DVI-D source can drive an HDMI monitor, or vice versa, by means of a suitable adapter or cable, but the audio and remote control features of HDMI won't be available. Additionally, without support for High-bandwidth Digital Content Protection (HDCP) on the display, the signal source may prevent the end user from viewing or recording certain restricted content. PCs with hardware HDMI output may require software support from Operating Systems such as Windows Vista. Linux currently supports video output through backward-compatibility with DVI.

Specifications

HDMI defines the protocol and electrical specifications for the signaling, pin-out, electrical, and mechanical requirements of the cable and connectors.

Connectors

The 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. The plug's outside dimensions are 13.9 mm wide by 4.45 mm high. Type A is electrically compatible with single-link DVI-D.
   A higher resolution version called Type B is defined in HDMI 1.0. Type B has 29 pins (21.2 mm wide) allowing it to carry an expanded video channel for use with very high-resolution future displays such as QXGA#WQUXGA (3840x2400). Type B is electrically compatible with dual-link DVI-D but isn't in general use.
   The Type C mini-connector is intended for portable devices. It is smaller than the Type A connector(10.42 mm by 2.42 mm) but has the same 19-pin configuration. It can be connected to a Type A connector using a Type A-to-Type C connector cable.

Cable

The HDMI cable can be used to carry video, audio, and device-controlling signals (CEC). HDMI cables are often more expensive than other video cables at retail stores. However, many on-line retailers and auction sites offer high-end HDMI cables at prices similar to coaxial and RCA cabling.

TMDS channel

The Transition Minimized Differential Signaling (TMDS) channel:

Carries video, audio, and auxiliary data via one of three modes 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.
Signaling method: Formerly according to DVI 1.0 spec. Single-link (Type A HDMI) or dual-link (Type B HDMI).
Video pixel rate: 25 MHz to 340 MHz (Type A, as of 1.3) or to 680 MHz (Type B). Video formats with rates below 25 MHz (for example 13.5 MHz for 480i/NTSC) are transmitted using a pixel-repetition scheme. From 24 to 48 bits per pixel can be transferred, regardless of rate. Supports 1080p at rates up to 120 Hz and WQSXGA.
Pixel encodings: xvYCC 4:4:4 (8–16 bits per component), sRGB 4:4:4 (8–16 bits per component), YCbCr 4:4:4 (8–16 bits per component), YCbCr 4:2:2 (8-12 bits per component)
Audio sample rates: 32 kHz, 44.1 kHz, 48 kHz, 88.2 kHz, 96 kHz, 176.4 kHz, 192 kHz.
Audio channels: up to 8.
Audio streams: any IEC61937-compliant stream, including high bitrate (lossless) streams (Dolby TrueHD, DTS-HD Master Audio).

Consumer Electronics Control channel

The Consumer Electronics Control (CEC) channel wiring is mandatory although implementation of CEC in a product is optional. The channel:

Uses the industry standard AV Link protocol.

Is used for remote control functions.

Is a one-wire bidirectional serial bus.

Is defined in HDMI Specification 1.0 and updated in HDMI 1.2a and again in 1.3a (added timer and audio commands). This feature is used to allow:

The user to command and control multiple CEC-enabled boxes with one remote control and

Individual CEC-enabled boxes to command and control each other without user intervention. 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's later than 11:00 p.m., for example, and the user doesn't specifically command the systems with the remote control, the systems turn off on command from the DVD player. Alternative names for CEC are Anynet (Samsung), Aquos Link (Sharp), BRAVIA Theatre Sync (Sony), Regza Link (Toshiba), RIHD (Onkyo), Simplink (LG), Viera Link/EZ-Sync (Panasonic/JVC), Easylink (Philips) and NetCommand for HDMI (Mitsubishi).

Content protection

HDMI can use HDCP to encrypt the signal if required by the source device. CSS, CPPM, and AACS requires the use of HDCP on HDMI when playing back encrypted DVD-Video, DVD-Audio, and Blu-ray Disc. According to HDCP Specification 1.2:

Beginning with HDMI CTS 1.3a, any system which implements HDCP must do so in a fully-compliant manner. HDCP compliance is itself part of the requirements for HDMI compliance.

The HDCP Repeater bit controls the authentication and switching/distribution of an HDMI signal.

Versions

Devices are manufactured to adhere to various versions of the specification, where each version is given a revision number. Each subsequent 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 an HDMI rating). The main thing to consider is if any current cable would be able to handle the increased bandwidth—for example the 10.2 Gbit/s 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).
A product listed as having an HDMI version doesn't necessarily mean that it'll have all of the features listed under the version classification: indeed, some of the features are optional. For example, in HDMI v1.3 it's optional to support the xvYCC wide color standard. This means if you've bought a camcorder that supports the wide color space (which for example is branded by Sony as "x.v.Color") you've to specifically check that the display supports both HDMI v1.3 and the xvYCC wide color standard.

HDMI 1.0

Released December 9, 2002.

Single-cable digital audio/video connection with a maximum bitrate of 4.9 Gbit/s. Supports up to 165 Mpixel/s video (1080p60 Hz or UXGA) and 8-channel/192 kHz/24-bit audio.

HDMI 1.1

Released May 20, 2004.

Added support for DVD Audio.

HDMI 1.2

Released August 8, 2005.

Added support for One Bit Audio, used on Super Audio CDs, up to 8 channels.

Availability of HDMI Type A connector for PC sources.

Ability for PC sources to use native RGB color-space while retaining the option to support the YC_BC_R CE color space.

Requirement for HDMI 1.2 and later displays to support low-voltage sources.

HDMI 1.2a

Released December 14, 2005.

Fully specifies Consumer Electronic Control (CEC) features, command sets, and CEC compliance tests.

HDMI 1.3

Released June 22, 2006.

Increases single-link bandwidth to 340 MHz (10.2 Gbit/s)

Optionally supports Deep Color with 30-bit, 36-bit, and 48-bit xvYCC, sRGB, or YC_BC_R compared to 24-bit sRGB or YC_BC_R in previous HDMI versions.

Incorporates automatic audio syncing (Audio video sync) capability.

Optionally supports output of Dolby TrueHD and DTS-HD Master Audio streams for external decoding by AV receivers. TrueHD and DTS-HD are lossless audio codec formats used on Blu-ray Discs and HD DVDs. If the disc player can decode these streams into uncompressed audio, then HDMI 1.3 isn't necessary, as all versions of HDMI can transport uncompressed audio.

Availability of a new Type C mini-connector for devices such as camcorders.

HDMI 1.3a

Released November 10, 2006.

Cable and Sink modifications for Type C

Source termination recommendation

Removed undershoot and maximum rise/fall time limits.

CEC capacitance limits changed

RGB video quantization range clarification

CEC commands for timer control brought back in an altered form, audio control commands added.

Concurrently released compliance test specification included.

HDMI 1.3b

Released March 26, 2007.

HDMI compliance testing revisions. Has no effect on HDMI features or functions since the testing is for products based on the HDMI 1.3a specification.

HDMI 1.3b1

Released November 9, 2007. Some companies offer amplifiers, equalizers, and repeaters that can string several standard (non-active) HDMI cables together. Due to accumulation of signal skew and clock jitter, however, the total cable length is limited to around 40 meters and no more than two equalizers and repeaters for 1080p.

HDMI and high-definition optical media players

Blu-ray Disc, introduced in 2006, offers new high-fidelity audio features that require HDMI for best results. Dolby Digital Plus (DD+), Dolby TrueHD, and DTS-HD Master Audio use bitrates exceeding TOSLINK's capacity. HDMI 1.3 can transport DD+, TrueHD, and DTS-HD bitstreams in compressed form. This capability allows a preprocessor or audio/video receiver with the necessary decoder to decode the data itself but has limited usefulness for Blu-ray.
Blu-ray permits "interactive audio" whereby the disc content tells the player to mix multiple audio sources together before final output. Most players will consequently handle audio-decoding internally and simply output LPCM audio all the time. Multichannel LPCM can be transported over an HDMI 1.1 (or higher) connection. As long as the audio/video receiver (or preprocessor) supports multi-channel LPCM audio over HDMI, and supports HDCP, the audio reproduction is equal in resolution to HDMI 1.3. Many of the cheapest AV receivers, however, don't support audio over HDMI and are often labeled as "HDMI pass through" devices.
Note that not all of the features of an HDMI version may be implemented in products adhering to that version since certain features of HDMI, such as Deep Color and xvYCC support, are optional.

HDMI revision	1.0	1.1	1.2/1.2a	1.3/1.3a/1.3b/1.3b1
Maximum signal bandwidth (MHz)	165	165	165	340
Maximum TMDS bandwidth (Gbit/s)	4.95	4.95	4.95	10.2
Maximum video bandwidth (Gbit/s)	3.96	3.96	3.96	8.16
Maximum audio bandwidth (Mbit/s)	36.86	36.86	36.86	36.86
Maximum resolution over single link at 24 bit/px	1920×1200p60	1920×1200p60	1920×1200p60	2560×1600p75
RGB
YC_BC_R
xvYCC
Deep Color
Maximum Color Depth (bit/px)	24	24	24	48
Consumer Electronic Control (CEC)
Updated list of CEC commands
Auto lip-sync
8 channel/192 kHz/24-bit audio capability
DVD-A support
SACD (DSD) support
TrueHD bitstream capable
DTS-HD Master Audio bitstream capable
BD/HD DVD video and audio at full resolution

CEC has been in the HDMI specification since version 1.0 but has only begun to be used in CE products with HDMI version 1.3. � Large number of additions and clarifications for CEC commands. One addition is CEC command allowing for volume control of an AV receiver.

Playback of SACD may be possible for older revisions if the signal source (such as the Oppo 970) converts to LPCM. For those receivers that have only PCM DAC converters and not DSD this means that no additional resolution loss occurs. � Even for audio bitstream formats that a given HDMI revision can't transport it may still be possible to decode the bitstream in the player and transmit the audio as LPCM.

Competition with DisplayPort

One recent competitor to HDMI is the DisplayPort standard which had version 1.0 approved in May 2006 and is supported in a few computer monitors. Currently no CE displays or AV receivers have been released that support DisplayPort.
There are a few advantages that HDMI has over DisplayPort such as support for the xvYCC color space, Dolby TrueHD and DTS-HD MA bitstream support, CE control signals, and compatibility with DVI. DisplayPort has an advantage that at the moment it's royalty/license free which might allow it to be cheaper to implement. So far though DisplayPort has increased costs for the few computers monitors that have used it since they included support for both DisplayPort and HDMI. Most of the backers of DisplayPort are computer companies with its largest supporter being Dell which in January 2008 released a computer monitor that supported both DisplayPort and HDMI.

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