HDMI

(High-Definition Multimedia Interface) A digital interface for audio and video signals designed as a single-cable solution for home theater and consumer electronics equipment. Introduced in 2002 by the HDMI consortium, HDMI is electrically identical to video-only DVI, but it also includes audio, and HDMI plugs and sockets are considerably smaller.

HDMI/DVI Compatibility
HDMI is backward compatible with DVI, and HDMI-to-DVI and DVI-to-HDMI adapters and cables let video signals be interchanged between HDMI and DVI devices. For example, a computer monitor that has an HDMI socket for digital input typically includes a DVI-to-HDMI cable for computers with DVI output.

If a cable set-top box has DVI output, and the TV has HDMI input, a DVI-to-HDMI cable is required. Since DVI is only video, the audio from the cable TV box must be wired separately to the TV (see illustration below).

HDMI 1.3
Prior to Version 1.3, HDMI supported a clock rate of 165MHz or 4.95 Gbps, transferring 165 million 24-bit pixels per second. Introduced in 2006, HDMI 1.3 increased the rate to 340MHz (10.2 Gbps) to accommodate 2560x1440 HDTV resolution with pixels up to 48 bits, known as "deep color." HDMI also supports eight channels of 24-bit uncompressed audio at 192kHz.

HDMI 1.3 uses two types of cables. HDMI Category 1 cables are rated for 720p and 1080i TVs. For higher resolutions, HDMI Category 2 cables are required. See HDTV.

Although HDMI has enhanced protocols that support audio and auxiliary data packets, an HDMI source can detect a DVI device on the other end and switch to the DVI protocol. For more information, visit HDMI Licensing, LLC (www.hdmi.org). See HDMI switch, HDMI CEC, DVI, HDCP and UDI.


   HDMI
   Version    Features

   1.0        Original bandwidth of 4.95 Gbps

   1.1        Support for DVD-Audio

   1.2        Support for SACD audio

   1.3        Increased bandwidth to 10.2 Gbps
              Support for TrueHD and DTS-HD audio

   1.3a       Technical improvements

   1.3b       Stricter compliance with 1.3 spec

HDMI Vs. DVI

Although the 19-pin HDMI plug (left) is considerably smaller than the 19-pin DVI plug on the right, HDMI also includes digital audio.

An HDMI/DVI Socket

This LCD TV has only one digital video port for input, but because it is HDMI, it can accommodate both HDMI and DVI sources. An HDMI source requires only one HDMI cable, which carries both audio and video to the TV. A DVI source uses a DVI-to-HDMI cable for the video and requires a separate pair of stereo cables (analog) for the complete audio/video hookup.

An HDMI Switch

HDMI switches allow several HDMI sources to plug into TVs that have only one HDMI input. This 3X1 (3 in - 1 out) unit from Octava switches between three inputs. See HDMI switch. (Image courtesy of Octava Inc., www.octavainc.com)