High-Definition Multimedia Interface
HDMI or High Definition Multimedia Interface is meant for transfer of digital audio and digital video from DVD players, set top boxes etc. to TVs, projectors etc. HDMI is the standard that was developed by Hitachi, Panasonic, National, Quasar, Philips, Silicon Image, Sony, Thomson, and Toshiba during the year 2002. The aim behind developing such an interface is to make transmission of digital audio/video between compatible devices an easy task by using just a single cable rather than using separate cables for audio and video. HDMI supports the transfer of any uncompressed video and audio formats over a single cable. Over the introduction of HDMI cables, connection between video/audio sources and displays has become user friendly and removed all snake-like wirings from households. HDMI supplies high definition quality audio and video without distortion and works well with displays such as, LCD, LED, Plasma and DLP projectors etc. HDMI output match pixel-by-pixel with the displays.
Older TVs take analog inputs and display comes under Standard Definition with an aspect ratio of 4:3. HDMI output is digital and does the necessary conversions for Standard TVs. But now with the introduction of HDTVs, which take digital inputs, use of HDMI output has taken the display to an all new height. The aspect ratio of HDTV is 16:9, with rectangular display, with resolution up to 1092*1080 pixels. HDTVs need data at a higher rate compared to older TVs, in that case, HDMI comes with digital data output, so that, it avoids conversion of analog to digital format and faster processing for HDTVs.
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The pin-out configuration of HDMI male connector is shown above. From pins, HDMI signals go through twisted pair cable. HDMI cable contains 19 wires combined to single cable and carries a bandwidth of 10.2 GBps.
HDMI working is explained with the help of communication protocols such as Display Data Channel (DDC), Transition Minimized Differential Signaling (TMDS) and Consumer Electronics Control (CEC), which are physically separate.
Transition Minimized Differential Signaling (TMDS)
HD-DVD players provide an audio/video signal to HDTV via HDMI cable and the signals undergo encoding before getting displayed on HDTV. Transition Minimized Differential Signaling (TMDS), is an encoding method used by HDMI for the transfer of data from one point to another without degrading the information over the distance of the cable. This encoding method is used by most of the interfaces that transmit audio/video signals like, DVI, HDMI etc. Differential transmission method is used in the encoding with 8-bit information encoded into 10-bit signal. The sender does the encoding process to reduce the transition number from zero and one. As these transitions increases the chances of degradation, the encoding step improves the signal quality. HDMI cable consists of twisted pair cable, with one carrying the original signal and the other cable carrying the inverse of the original signal. The HDTV at the receiving end does the decoding operation and checks between the original signal and its inverse, that is, checks the differential and nullifies the degradation in the signal along the length of the cable.
Display Data Channel (DDC)
DDC is a set of communication protocols that defines certain rules and regulations on the connection between a graphics adapter and computer display. This protocol allows communication between the display and adapter on the display formats the monitor can support and enables the adjustment of display parameters such as contrast, sharpness etc.
The support of Enhanced Display Data Channel (E-DDC) is required for HDMI, which provides the information to the sender about the video formats supported by the receiver. The information of video formats supported by receiver is obtained from the E-EDID information from the source. E-DDC is used by HDMI to support a speed of 100kbps during I2c standard mode and also gives an optional speed of 400kbps during fast mode. Plug and Play experience is provided to the displays by DDC.
Consumer Electronics Control (CEC)
User gets the privilege of controlling CEC-enabled two or more devices with the help of a single remote controller of any of these devices. CEC also allows the commanding and controlling of CEC supporting devices by mutual intervention. CEC-enabled devices can send instructions between each other. One Touch Play, Deck Control, One Touch Record, Tuner Control etc. are the functions provided by CEC.
The outside dimensions of plug (male) connector are 13.9 mm × 4.45 mm and the inside connection of receptacle (female) connector are 14 mm × 4.55 mm. Type A connectors have 19 pins and a bandwidth that supports HDTV, SDTV (Standard Definition Television) etc.
Type B connector dimensions are 21.2 mm × 4.45 mm and it is designated to use in high definition, high resolution display devices in future with 6 differential pairs in place of 3. Type B connectors and dual-link DVI-D are electrically compatible.
Type C is a mini connector that is being used in portable devices and consists of 19 pins and measures a dimension of 10.42 mm × 2.42 mm. These type of connectors can use type A-to-type C cable to connect with type A connector.
Type D is a micro-connector with a measurement of 6.4 mm × 2.8 mm and 19 pins with different pin assignment from that of Type A and Type C.
To avoid cables from vibrating loose there is a locking tab and a shell exists to avoid dirt from signal interaction. Both are obtained with Automotive Connection System. Automotive type is connected to consumer cables using a relay connector.
HDMI comes in 5 versions, mainly, 1.0, 1.1, 1.2, 1.3 and 1.4.
HDMI versions vs. HD Resolutions
Features of HDMI
- High-Bandwidth Digital Copy Protection (HDCP)
Data protection in HDMI is done by High-Bandwidth Digital Copy Protection (HDCP), which is actually an authentication protocol. Extended display identification data (EDID) chip found on all home theatre device stores encryption and identification data for the particular device. A sender, HD-DVD player, does the checking of the authentication key with the receiver, HDTV. If check out happens, sending device generates next key to link with receiving device, thereby shared secret is created. Whole process is said to be Handshake and happens simultaneously. The sender is supposed to encode and protect the information using a key, which the receiver should use to retrieve the information. If the information is intercepted by an unauthorized receiver, the sender breaks the transmission. The sender also ensures that the system is secure and key is unchanged. HDCP is supported by all HDMI-compatible equipment.
The single link HDMI bandwidth increases from 165MHz to 340MHz with HDMI 1.3 version. The bandwidth increases to meet the features required for display at high definition devices such as, higher resolutions, high frame rate and deep colors.
To improve the connectivity between small portables devices and displays, HDMI has come up with HDMI 1.3 version which is a smaller connection option.
With increased use of complex DSPs by electronics devices for the purpose of content detailing and clarity, video and audio synchronization has become a matter of consideration and requires adjustments at end-user level. The version 1.3 of HDMI allows automatic synchronization of audio with utmost accuracy.
HDMI vs DVI
HDMI has an upper hand over DVI-D by using audio and video signals as digital signals over a single cable whereas DVI-D uses digital connection for video transfer but audio signal is carried using another cable. Component Video and S-video are analog connections. HDMI is meant for higher resolutions when compared to DVI. HDMI connector size is smaller when compared to DVI connectors. HDMI carries audio and video signals over a twisted pair copper cable whereas DVI carries just video signal. There are DVI-HDMI adapters avail
HDMI supplies audio and video signals with utmost quality when compared to any other analog or digital counterparts. Loss-less transmission is carried out using HDMI cables.
HDMI transfer signals after encoding it with key from the sender part. Only the receiver with the desired key can retrieve information which improves the security of the information. This security system also prevents technical people from intercepting the transmitted data.
HDMI enables storage, transmission and viewing of digital signals without any big change as there is no conversion in HDMI, when compared to other interface standards. Also degradation in signal strength is less.
HDMI comes with a single cable consisting of a twisted pair copper cable for the transmission of high quality audio and video signals. This avoids the use of all messy wiring for transmission.
HDMI is compatible with DVI which enables those devices with DVI enabled to send HD data to the displaying devices.
HDMI support most of the audio and video formats like NTSC, PAL, 720, 1080p etc.
HDMI Cat1 cable extends a maximum up to 35m and HDMI Cat2 cable extends a maximum of 10m for full capacity. Exceeding this limit, extenders/repeaters are used. Still, HDMI has its limitations on extension.
HDMI cables are expensive depending on the length of the meter when compared to their analog counterparts.
Authentication delays can bring about blank screens and screen flashing errors also occur.
HDMI cable connection, is similar to that of USB, is damage prone and should be safeguarded from accidental knocks.
HDMI is used for the connection of sources with digital audio/video, like HD-DVD players, Computers, Set-top boxes. It is a connector that is all set to replace all analog/digital connectors in the current scenario.