HDMI

HDMI is a brand of proprietary digital interface used to transmit video and audio signals between devices. It is commonly used to connect devices such as televisions, computer monitors, projectors, gaming consoles, and personal computers. HDMI supports uncompressed video and either compressed or uncompressed digital audio, allowing a single cable to carry both signals.
Introduced in 2003, HDMI largely replaced older analog video standards such as composite video, S-Video, and VGA in consumer electronics. It was developed based on the CEA-861 standard, which was also used with the earlier Digital Visual Interface. HDMI is electrically compatible with DVI video signals, and adapters allow interoperability between the two without signal conversion or loss of quality. Adapters and active converters are also available for connecting HDMI to other video interfaces, including the older analog formats, as well as digital formats such as DisplayPort.
HDMI has gone through multiple revisions since its introduction, with each version adding new features while maintaining backward compatibility. In addition to transmitting audio and video, HDMI also supports data transmission for features such as Consumer Electronics Control, which allows devices to control each other through a single remote, and the HDMI Ethernet Channel, which enables network connectivity between compatible devices. It also supports the Display Data Channel, used for automatic configuration between source devices and displays. Newer versions include advanced capabilities such as 3D video, higher resolutions, and expanded color spaces. The Audio Return Channel and Enhanced Audio Return Channel allow audio to be sent from a display back to an audio system over the same HDMI cable. Smaller connector types, Mini and Micro HDMI, were also introduced for use with compact devices like camcorders and tablets.
nearly 14 billion HDMI-enabled devices have been sold worldwide, making it one of the most widely adopted audio/video interfaces in consumer electronics.

History

The HDMI founders were Hitachi, Panasonic, Sanyo, Philips, Silicon Image, Sony, Thomson, and Toshiba. Intel contributed the HDCP copy protection system. The new format won the support of motion picture studios Fox, Universal, Warner Bros. and Disney, along with content distributors DirecTV, EchoStar and CableLabs.
The HDMI founders began development on HDMI 1.0 on April 16, 2002, with the goal of creating an AV connector that was backward-compatible with DVI. At the time, DVI-HDCP and DVI-HDTV were being used on HDTVs. HDMI 1.0 was designed to improve on DVI-HDTV by using a smaller connector and adding audio capability, enhanced YCbCr| capability, and consumer electronics control functions.
The first Authorized Testing Center, which tests HDMI products, was opened by Silicon Image on June 23, 2003, in California, United States. The first ATC in Japan was opened by Panasonic on May 1, 2004, in Osaka. The first ATC in Europe was opened by Philips on May 25, 2005, in Caen, France. The first ATC in China was opened by Silicon Image on November 21, 2005, in Shenzhen. The first ATC in India was opened by Philips on June 12, 2008, in Bangalore. The HDMI website contains a list of all the ATCs.
According to In-Stat, the number of HDMI devices sold was 5 million in 2004, 17.4 million in 2005, 63 million in 2006, and 143 million in 2007. HDMI has become the de facto standard for HDTVs, and according to In-Stat, around 90% of digital televisions in 2007 included HDMI. In-Stat has estimated that 229 million HDMI devices were sold in 2008. On April 8, 2008, there were over 850 consumer electronics and PC companies that had adopted the HDMI specification. On January 7, 2009, HDMI Licensing, LLC announced that HDMI had reached an installed base of over 600 million HDMI devices. In-Stat estimated that 394 million HDMI devices would sell in 2009 and that all digital televisions by the end of 2009 would have at least one HDMI input.
On January 28, 2008, In-Stat reported that shipments of HDMI were expected to exceed those of DVI in 2008, driven primarily by the consumer electronics market.
In 2008, PC Magazine awarded a Technical Excellence Award in the Home Theater category for an "innovation that has changed the world" to the CEC portion of the HDMI specification. Ten companies were given a Technology and Engineering Emmy Award for their development of HDMI by the National Academy of Television Arts and Sciences on January 7, 2009.
On October 25, 2011, the HDMI Forum was established by the HDMI founders.Also on the same day HDMI Licensing, LLC announced that there were over 1,100 HDMI adopters and that over 2 billion HDMI-enabled products had shipped since the launch of the HDMI standard.
On January 8, 2013, HDMI Licensing, LLC announced that there were over 1,300 HDMI adopters and that over 3 billion HDMI devices had shipped since the launch of the HDMI standard. The day also marked the 10th anniversary of the release of the first HDMI specification.
nearly 10 billion HDMI devices had been sold.

Specifications

The HDMI specification defines the protocols, signals, electrical interfaces and mechanical requirements of the standard. The maximum pixel clock rate for HDMI 1.0 is 165 MHz, which is sufficient to allow 1080p and WUXGA at 60Hz. HDMI 1.3 increases that to 340 MHz, which allows for higher resolution across a single digital link. An HDMI connection can either be single-link or dual-link and can have a video pixel rate of 25 MHz to 340 MHz or 25 MHz to 680 MHz. Video formats with pixel rates below 25 MHz are transmitted over TMDS links using a pixel-repetition scheme.

Audio/video

HDMI uses the Consumer Technology Association/Electronic Industries Alliance 861 standards. HDMI 1.0 to HDMI 1.2a uses the EIA/CEA-861-B video standard, HDMI 1.3 uses the CEA-861-D video standard, and HDMI 1.4 uses the CEA-861-E video standard. The CEA-861-E document defines "video formats and waveforms; colorimetry and quantization; transport of compressed and uncompressed LPCM audio; carriage of auxiliary data; and implementations of the Video Electronics Standards Association Enhanced Extended Display Identification Data Standard ". On July 15, 2013, the CEA announced the publication of CEA-861-F, a standard that can be used by video interfaces such as DVI, HDMI, and LVDS. CEA-861-F adds the ability to transmit several Ultra HD video formats and additional color spaces.
To ensure baseline compatibility between different HDMI sources and displays all HDMI devices must implement the sRGB color space at 8 bits per component. Ability to use the color space and higher color depths is optional. HDMI permits sRGB 4:4:4 chroma sampling, xvYCC 4:4:4 chroma sampling, 4:4:4 chroma sampling, or 4:2:2 chroma subsampling. The color spaces that can be used by HDMI are ITU-R BT.601, ITU-R BT.709-5 and IEC 61966-2-4.
For digital audio, if an HDMI device has audio, it is required to implement the baseline format: stereo PCM. Other formats are optional, with HDMI allowing up to 8 channels of uncompressed audio at sample sizes of 16 bits, 20 bits, or 24 bits, with sample rates of 32kHz, 44.1kHz, 48kHz, 88.2kHz, 96kHz, 176.4kHz, or 192kHz. HDMI also carries any IEC 61937-compliant compressed audio stream, such as Dolby Digital and DTS, and up to 8 channels of one-bit DSD audio at rates up to four times that of Super Audio CD. With version 1.3, HDMI allows lossless compressed audio streams Dolby TrueHD and DTS-HD Master Audio. As with the video, audio capability is optional. Audio return channel is a feature introduced in the HDMI 1.4 standard. "Return" refers to the case where the audio comes from the TV and can be sent "upstream" to the AV receiver using the HDMI cable connected to the AV receiver. An example given on the HDMI website is that a TV that directly receives a terrestrial/satellite broadcast, or has a video source built in, sends the audio "upstream" to the AV receiver.
The HDMI standard was not designed to pass closed caption data to the television for decoding. As such, any closed caption stream must be decoded and included as an image in the video stream prior to transmission over an HDMI cable to appear on the DTV. This limits the caption style 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 that sends an upscaled 720p/1080i format via HDMI to an HDTV has no way to pass Closed Captioning data so that the HDTV can decode it, as there is no line 21 VBI in that format.

Communication channels

HDMI has three physically separate communication channels, which are the VESA DDC, TMDS and the optional CEC. HDMI 1.4 added ARC and HEC.

Display Data Channel (DDC)

The Display Data Channel is a VESA standard communications channel based on the I²C bus specification. HDMI specifically requires the device implement the Enhanced Display Data Channel, 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 can take. HDMI requires that the E-DDC implement I²C standard mode speed and allows it to optionally implement fast mode speed.
I²C address 0x74 on the DDC channel is actively used for High-bandwidth Digital Content Protection.

Transition-minimized differential signaling (TMDS)

on HDMI interleaves video, audio and auxiliary data using three different packet types, 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, audio and auxiliary data are transmitted within a series of packets. The control period occurs between video and data island periods.
Both HDMI and DVI use TMDS to send 10-bit characters that are encoded using 8b/10b encoding that differs from the original IBM form 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. 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. 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. Each data island period can contain up to 18 packets. 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. Among these are the general control packet and the gamut metadata packet. The general control packet carries information on AVMUTE and color depth. The gamut metadata packet carries information on the color space being used for the current video stream and is required for xvYCC.