What Is HDMI?

Posted by Scott Davies on

HDMI stands for High-Definition Multimedia Interface. HDMI provides a compact AV (audio/video) interface that enables the transfer of uncompressed digital AV data. Data originates from a HDMI-compliant device, termed the source or input, which is connected to a display unit. Sources can include DVD, HD DVD and Blu-Ray players, personal computers, HDMI-enabled set-top boxes and some types of camcorder. Display devices can include televisions, computer monitors and projectors.

HDMI 1.4
The current standard for HDMI, announced in 2009, is 1.4. This new standard introduced many new features; as a result, HDMI 1.4-compliant equipment is not compatible with equipment enabled for earlier versions of HDMI. According to HDMI.org, the official website for the HDMI standard, "most of the new features introduced in HDMI 1.4 will require a new HDMI chip to enable, and cannot be upgraded via firmware." Consumers wishing to adopt HDMI 1.4 will need to buy new cables and new HD TV equipment.

Color Spaces
HDMI 1.4 includes support for more color spaces: sYCC601, Adobe RGB, and Adobe YCC601. Each of these color spaces defines a palette of different colors. The addition of new color spaces is designed to improve the accurate reproduction of colors when viewing digital images on digital televisions and other displays.

Audio Return Channel
If a television has an internal content source -- for example, a built-in tuner or DVD player -- the new Audio Return Channel enables the television to relay audio data via the HDMI cable to the receiver. This removes the need to use an additional cable to send data "upstream" -- all communication can be handled by a single HDMI cable.

Higher Definition
The resolution available in most current devices is 1080 pixels. HDMI 1.4 provides support for 4K x 2K resolutions, roughly quadruple that resolution. HDMI 1.4 supports several different resolution formats, including 3840 x 2160 pixels at frequencies of 24Hz, 25Hz and 30Hz; and 4096 x 2160 pixels at 24Hz.

3D Support
Once an expensive gimmick, 3D television is gaining ground as a viable and desirable option for high-end home entertainment. It's therefore unsurprising that HDMI 1.4 offers support for several 3D formats. These include "2D plus depth" methods, frame, line and field alternative methods and "side by side" methods. The HDMI 1.4 specification can also process dual-stream 3D resolutions up to 1080p.

Ethernet Channel
Previous specifications of HDMI have required a separate cable to establish an ethernet connection between the source and the display device. HDMI 1.4 features support for an integrated ethernet channel. As well as removing the need for an extra ethernet cable, this also enables web-capable HDMI 1.4-compliant devices to share their Internet connections with each other. This could allow users to set up one device, with Internet and HDMI 1.4 connectivity, to act as a hub for several different devices.

New Connection Options
HDMI 1.4 specifies a Type E Automotive Connection System. This can be used in a vehicle, to distribute HD content to different devices. The new HDMI 1.4 Micro Connector is designated Type D. It's designed for use with devices such as digital cameras, personal media players and cellphones, allowing high-definition content to be distributed to these smaller units


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