The High-Definition Multimedia Interface (HDMI) is an all-digital audio/video interface capable of transmitting uncompressed streams. HDMI provides an interface between any compatible digital audio/video source, such as a set-top box, a DVD player, a PC, a video game system, or an AV receiver and a compatible digital audio and/or video monitor, such as a digital television (DTV).

HDMI supports any TV or PC video format, including standard, enhanced, or high-definition video, plus multi-channel digital audio on a single cable. It is independent of the various DTV standards such as ATSC and DVB, as these are encapsulations of the MPEG movie data streams, which are passed off to a decoder, and output as uncompressed video data on HDMI. HDMI encodes the video data into TMDS for transmission digitally over HDMI.

Devices are manufactured to adhere to various versions of the specification, where each version is given a number, such as 1.0 or 1.3. Each concurrent version of the specification uses the same cables, but increases the throughput and capabilities of what can be transmitted over the cable. For example, previously, the maximum pixel rate of the interface was 165Mpixels/second, sufficient for supporting 1080p at 60Hz or WUXGA (1920x1080), but HDMI 1.3 increased that to 340Mpixels/second, providing support beyond the highest resolution computer monitors available today.

HDMI also includes support for 8-channel uncompressed digital audio at 192kHz sample rate with 24 bits/sample as well as any compressed stream such as Dolby Digital, or DTS. HDMI supports up to 8 channels of one-bit audio, such as that used on Super Audio CDs at rates up to 4x that used by SuperAudio CD. With version 1.3, HDMI now also supports very high bitrate lossless compressed streams such as Dolby TrueHD and DTS-HD Master Audio.

The standard Type A HDMI connector has 19 pins, and a higher resolution version called Type B, has been defined, although it is not yet in use. Type B has 29 pins, allowing it to carry an expanded video channel for use with very high-resolution future displays. Type B is designed to support resolutions higher than WQSXGA (3200x2048).

Type A HDMI is backward-compatible with the single-link Digital Visual Interface carrying digital video (DVI-D or DVI-I, but not DVI-A) used on modern computer monitors and graphics cards. This means that a DVI-D source can drive an HDMI monitor, or vice versa, by means of a suitable adapter or cable, but the audio and remote control features of HDMI will not be available. Additionally, without support for High-Bandwidth Digital Content Protection (HDCP) on the display, the signal source may prevent the end user from viewing or especially copying certain restricted content. (While all HDMI displays currently support HDCP, most DVI PC-style displays do not.) Type B HDMI is similarly backward-compatible with dual-link DVI.