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Written By: 

Preeti Jain

Today, many of us are in the process of removing their CRT TVs and shopping for the new hype in the TV market –High Definition TVs. And if you happen to be one of them, you surely would have come across the term HDMI. Not only TV, HDMI port is available on home theatres, play stations, HD-DVDs and many others.


The difference between a HDTVs and old TVs (also, now known as standard definition TVs) lies in the technology. Older TVs were analog, whereas HDTVs are digital. Older TVs used interlacing, aspect ratio of 4:3 and picture resolution of about 704 X 480 pixels. HDTVs use progressive scanning, aspect ratio of 16:9, picture resolutions up to 1920 X 1080 pixels. In other words, HDTVs use higher refresh rates, wider displays as well as enhanced picture resolution. What this implies is that HDTVs require higher amount of data to be processed and also at a faster rate compared to standard TVs.

To handle larger amount of data at faster rates, a standard called HDMI High Definition Multimedia Interface was evolved. The standard is basically a set of guidelines used for providing high bandwidth connection between the devices (digital in nature). Subsequent sections will discuss the details of HDMI
An industry-leading technology HDMI is an acronym for High-Definition Multimedia Interface and is a de-facto standard for connections between high-definition (HD) digital equipments, e.g., HDTVs, personal computers, cameras, camcorders, gaming consoles, tablets, Blu-ray players, smart phones, and  many others supporting HD signals. HDMI is the first industry-supported, uncompressed all-digital audio/video interface. To interface any audio/video source (for e.g. Set-top Box, DVD Player, etc.) and an audio/video monitor (Digital TVs), HDMI is being used and is the technology of future.
HDMI technology dramatically simplifies cabling and provides customers with the highest-quality HD experience. HDMI delivers all contents- digital audio, video as well as control signals via a single cable. HDMI has support for standard, enhanced or high definition video as well as multichannel video on a single cable. It transmits all HDTV standards and supports 8-channel, uncompressed digital audio and all presently-available compressed formats. In addition, it has spare bandwidth to accommodate future upgrades.
Representational Images of HDMI Cables
Fig. 1: Representational Images of HDMI Cables
Image Showing a Typical HDMI Interface
Fig. 2: Image Showing a Typical HDMI Interface
Compared to its predecessors (Component Video, S-Video and Composite Video, which were all analog interfaces), HDMI interface is all digital interface and carry uncompressed signals.
HDMI was founded by seven leading consumer electronics manufacturers which include Panasonic Corporation, Philips, Hitachi, Sony, Toshiba, Technicolor, and Silicon Image.  HDMI is also supported by producers of motion pictures including Universal, Fox, Warner Bros. and Disney.  Many system operators including DirecTV, EchoStar (Dish Network) and CableLabs also support HDMI.
HDMI specifications and compliance are imposed by an organization called HDMI LLC, which is governed by the seven founding companies. So far, HDMI Specifications have been adopted by over 1200 largest consumer electronics, personal computers and cellphone manufacturers. HDMI is a standard feature in over 1 billion consumer products.
In 2011, HDMI Forum was created by the HDMI Founders with an objective to nurture future development of the technology, to enable companies to contribute in the growth of the HDMI Specification. Approximately sixty of the largest consumer electronics, personal computers and semiconductor companies have joined their hands to make HDMI Specification better and widely adopted.
First HDMI 1.0 specification was released in 2002. Since then the specifications have been updated quite a few times to incorporate new features into the standard. Version numbers 1.x have marked these updates. Latest versions are made compatible with devices/systems designed to support previous standard. Of course, it will not add features to the system to your existing products.
·                     HDMI 1.0:
Released in Dec. 2002, it defined a single digital audio video interface with a maximum speed of 4.95 Gbps ( 3.96 Gbps of video BW+ 8 nos. of 192 KHz, 24-bit-bit audio).
·                     HDMI 1.1:
HDMI 1.1 was released in May 2004 and it added support for DVD Audio.
·                     HDMI 1.2: 
HDMI 1.2 was released in Aug. 2005. It provided extra features
·                     An extra support for 1- Bit audio format
·                     Use HDMI Type A connector for PC,
·                     Option (for PC) to use their native RGB colour space while extending support to the YCbCr CE colour space as well.
·                     Included constraint for HDMI 1.2 and later displays to support future low-voltage sources.
·                     HDMI 1.2a:
HDMI 1.2a fully specified Consumer Electronic Control (CEC) features, command sets and EC compliance tests. Compliance Test Specification (CTS) 1.2a contained additional requirements for cable and connector testing. It also mandated certification from Authorized Testing Center (ATC)
·                     HDMI 1.3:
HDMI 1.3 specification was released in June 2006 and it offered following features
·                     Greater Bandwidth
HDMI 1.3 increased the bandwidth by more than a double, i.e., from 165 MHz (4.95 Gbps) to 340 MHz (10.2 Gbps). Greater bandwidth offered higher resolutions, higher refresh rates and deep colours.
·                     Deep Colours
Previous HDMI versions supported 8-bit colour depth (RGB or YCbCr), i.e., 24 bit/pixel ~ 16 million colours. HDMI 1.3 supports 10-bit, 12-bit and 16-bit colour depth thereby offering more than 1 billion colours. Deeper colour palettes produce video more like original film. An example of tonal transitions with limited colour palette and with deep colour palette is shown below.
Rainbow Spectrum
Fig. 3: Rainbow Spectrum
·                     Extended colour space:
HDMI 1.3 have extended support to next generation HD Colour space standard, i.e., IEC 61966-2-4 xvYCC colour standard (Also known as for “x.v.Color™”). It takes full advantage of the modern digital displays Vs older CRT technology.
·                     Lossless audio:
In addition to provide support for uncompressed digital audio formats and all presently-available compressed formats (Dolby® Digital and DTS®); HDMI 1.3 has extended support for novel lossless compressed audio formats such as Dolby TrueHD and DTS-HD Master Audio™. Lossless audio formats maximise audio performance and provide true digital cinema experience.
·                     Lip Sync Compensation:
Advanced video processing in HDTVs sometimes introduces a delay in video output relative to audio resulting in loss of “lip sync”. HDMI 1.3 allows consumer electronic devices to automatically compensate for such timing difference and thereby resulting in synchronised audio and video and more enjoyable viewing experience.
·                     Type-C Mini Connector:
HDMI 1.3 offers a new, thinner, shorter and narrower connector option, i.e., Type-C mini connector. It is compatible with existing type-A connector. The plug is slightly smaller but chassis receptacle is much smaller. This connector caters to the demand of seamless connectivity of larger number of portable devices like HD cameras and camcorders.

HDMI - Version Contd...

·                     HDMI 1.4:
HDMI 1.4 offers additional features:
·                     HDMI Ethernet Channel:
HDMI Ethernet channel provides an easy connection to Internet and to all devices. HDMI Ethernet channel provides a high bandwidth Ethernet channel to connect home theatre devices enabling internet connection sharing, device-to-device content distribution, recording/ copying over HDMI, current and future IP-based applications such as DLNA, UPnP, IPTV, LiquidHD™ and others.
·                     Audio Return Channel:
In cases where audio is sent directly to the HDTV, current systems require an extra cable to send audio “upstream” to the A/V Receiver for processing. With the HDMI Audio Return Channel, cabling is simplified by combining the upstream audio capability into a single HDMI cable
Pictorial Presentation of Arc Audio Return Channel
Fig. 4: Pictorial Presentation of Arc Audio Return Channel
·                     3D Support:
The HDMI 1.4 Specification has established a critical infrastructure for implementing 3D in the home. HDMI 1.4 defines common 3D formats and resolutions. It provides 3D support for up to 1080p resolution, supports 3D structures like Half side-by-side, Full side-by-side, Line alternative, Field alternative, Left + Depth, Left + Depth + Gfx + Gfx Depth, and Frame packing.
·                     4K Support:
The HDMI 1.4 Specification support same resolution as digital theatres. It supports resolutions upto 4 times the resolution of 1080.
·                     Content Type:
The Content Type feature enables real-time signaling of content types between display and source devices. For example, if the source sends game content, the TV recognizes the content as “game” and optimizes the video processer for game content.
·                     More Color Spaces:
HDMI 1.4 supports digital still camera - specific color spaces, i.e., sYCC601, AdobeRGB, AdobeYCC601 thereby enabling consistency and accuracy between digital cameras and HDTVs.
·                     New Connector:

New HDMI Connectors

Fig. 5: New HDMI Connectors

HDMI 1.4 introduced yet another smaller connector to cater demands of portable devices, still providing same electrical performance as HDMI standard and Mini connectors.

New HDMI Connectors

Fig. 6: Graphic Image Showing Insides of New HDMI Connectors

It also introduced automotive HDMI connector for connection of HDMI devices in a car. This connector can withstand the rigors of an automotive environment

HDMI – Specifications

·                     Audio
HDMI supports 8-channel of audio with resolution of 24 bits and sampling rates up to 192 KHz, thereby supporting uncompressed digital audio and all presently-available compressed formats.  HDMI 1.3 also supports audio streams such Dolby TrueHD and DTS-HD Master Audio which are lossless and compressed. HDMI 1.4 also provides Audio Return Channel (ARC).
·                     Video
HDMI supports existing HD video formats (720p, 1080p and 1080i). It has got the flexibility to support enhanced video formats as well as NTSC and PAL (standard definition formats).
Video data can use pixel sizes of 24, 30, 36 or 48 bits. Color depths greater than 24 bits are defined to be “Deep Color” modes. Encoding of video pixels can be done in either RGB, YCBCR 4:2:2 or YCBCR 4:4:4 formats.
HDMI 1.0 - 1.2a uses the EIA/CEA (Electronic Industries Alliance/Consumer Electronic Association)-861-B video standard, HDMI 1.3 employs the CEA-861-D video standard, whereas HDMI 1.4 employs the CEA-861-E video standard.  HDMI 1.4 provides additional colors to support digital still cameras.
·                     Connectors
Five types of HDMI connectors are defined
·                     Type A: It is a 19-pin connector with dimensions being 13.9 mm × 4.45 mm.
·                     Type B: It is a 29-pin connector with dimensions being 21.2 mm × 4.45 mm. It uses 2 differential pairs(instead of three)
·                     Type C: Defined by HDMI 1.3, it is a 19-pin connector, but smaller than Type A, with dimensions being 10.42 mm × 2.42 mm.
·                     Type D: Defined by HDMI 1.4, it is a much smaller 19-pin connector with dimensions being 6.4 mm × 2.8 mm
·                     Type E: Defined by HDMI 1.4, it is defined for automotive applications. It is provided with locking tab.
·                     Cables
HDMI cable looks like a USB cable but is able to support high bandwidth of 5 Gbps which is more than sufficient to transport multichannel audio and video. There are two types of HDMI cables defined by HDMI 1.3
·                     Standard HDMI cables (or “category 1”): These cables have been tested for their performance at speeds of 75 MHz.
·                     High Speed (or “category 2”) HDMI cables: These cables have been tested for performance at speeds of 340 MHz; this is the maximum bandwidth currently achievable over an HDMI cable. High-Speed cables also support higher resolution displays (resolution upto 2560 x 1600).
HDMI 1.4 offers three more cable types
·                     Standard HDMI Cable with Ethernet : It  supports  100 Mbps, HDMI Ethernet Channel
·                     High Speed HDMI Cable with Ethernet:  It also supports 100 Mbps HDMI Ethernet Channel.
·                     Standard Automotive HDMI Cable
Maximum cable length is not specified; it is usually governed by the signal attenuation limits.
·                     Communication Channels
HDMI integrates data link (TMDS), status link (CEC), control link (DDC) and configuration protocols in a single miniature connector. The data link is unidirectional and low speed whereas control and status links are bidirectional and of high speed.
The HDMI cable and connectors have 4 differential channels; three of them are for audio, video and auxiliary data while one of them is used for TMDS clock.
HDMI carries an I2C specification based VESA DDC (Display Data channel). The DDC is utilized for configuration and status exchange between a single transmitter and a single receiver. The DDC is used by the transmitter to read the receiver’s Enhanced Extended Display Identification Data (E-EDID) in order to discover the receiver’s configuration and capabilities.
The optional CEC protocol is used for providing control functions between various audio and/or video products.
·                     Data Security
Along with HDCP (HD Content Protection), HDMI offers a safe audio/ video interface meeting security specifications of system operators and content providers.
·                     Compatibility with DVI
HDMI has full backward compatibility with DVI for digital TVs. HDMI DTVs display video received from DVI equipped products and DVI equipped TVs, (equipped with HDCP decoding) display video from HDMI sources.

Advantages, Application & Future

·                     Quality:
Being a digital interface, HDMI ensures all digital rendering of highest, crispest quality video by avoiding losses associated with analog interfaces such as Component Video or S-Video.
·                     Ease-of-use:
HDMI integrates multiple channel audio and video in one single cable, reducing the complexity, involved in variety of different A/V cables currently used in A/V systems. Single cable offers advantage during system upgrades/modification.  Single cable also results in cost reduction.
·                     Intelligence:
HDMI allows bidirectional communication between the DTV and the video source (such as a DVD player), enabling new functionality such as one-touch play and automatic configuration. HDMI also allows devices to automatically select and deliver the best according to the display that it is connected to.
·                     Support for multiple formats
Not only does it provide the functionality and the quality of a digital interface, HDMI supports uncompressed video formats along with multiple audio formats (standard/ multi-channel /stereo / surround sound).
HDMI is replacing all analog interfaces which used to be there in PCs and TVs. HDMI are available in almost all consumer electronics like digital cameras and camcorders, HD DVD players, Blu-ray disc, and mobiles and also on Personal computers and Tablets.
In times to come, jungle of all audio and video cables is likely to disappear and will be replaced by HDMI cables. HDMI is likely to become a standard on all CEs and PCs.