HDMI is the consumer interface standard for digital transmission of digital audio and digital video since 2002. Unlike DVI, HDMI also carries digital audio.

As the norm states: " .. digital connection standard designed to provide the highest possible uncompressed video and audio quality over a thin, easy-to-use cable with a simple, consumer-friendly connector .."

It combines video and audio into a single digital interface for audiovisual devices. HDMI signals are not compressed. It supports standard, enhanced, or high-definition video plus standard to multi-channel audio.
Data is transmitted by the transition minimized differential signaling (TMDS) protocol. The HDMI specification defines three data channels and one clock control channel. Channel 0, 1 and 2 are used for video and audio data. Channels 3 is used for clock data. HDMI (as DVI) supports two-way communication between the source and the destination device to automatically configure the display format. For content protection HDMI is (nearly) always combined with HDCP
See: HDCP.

HDMI carries the data streams on TMDS channels (Transition Minimized Differential Signaling) like DVI. DVI uses three TMDS channels for Single Link and three more TMDS channels for Dual Link. HDMI uses only three TMDS channels for the full bandwidth with the usual connector type A and C. There is also the not often used connector type B that can carry a dual link connection with up to 680MHz (HDMI 1.3).

HDMI connector type A	HDMI connector type C (mini)	inside the A connector (Oehlbach, Germany)

DVI: always 8 bit RGB transmission, Single Link or Dual Link
HDMI 1.3: YCbCr 4:4:4 (8–16 bits per component), YCbCr 4:2:2 (8–12 bits per component), xvYCC 4:4:4 (8–16 bits per component), sRGB 4:4:4 (8–16 bits per component) and supports 8 audio channels.

HDMI 1.3 increases the single-link bandwidth from 165MHz (4.95 gigabits per second) to 340 MHz (10.2 Gbps) to support the demands of future high definition display devices. The color depth is 30 bit, 36 bit and 48 bit (RGB or YCbCr), up to 16 bit per component. With HDMI 1.3 a maximum resolution of 1440p@120Hz (WQXGA) can be transmitted. HDMI supports also the protocols CEC (Consumer Electronics Control) and AV.link, both protocols for universal remote control.

HDMI 1.4, established in May 2009, adds an Ethernet channel as a bi-directional IP data channel to send and receive data at full Ethernet speeds up to 100Mbps, audio return channel, 3D over HDMI, 4K x 2K resolution support, a micro HDMI connector and an automotive connection system. There will be five different HDMI 1.4 cables. For 3D several 3D-formats are defined for HDMI-enabled devices: the frame alternative, line alternative and field alternative method. It is capable of handling dual-stream 3D resolutions up to 1080p. The 4K x 2K resolution support represents four times the pixel resolution of full HD 1920 x 1080.
HDMI 1.4 includes support for the color systems Adobe RGB, Adobe YCC601 and sYCC601 for a more accurately color reproduction viewing digital images.

HDMI supports PC formats and video formats. Some consumer devices with HDMI input don't accept PC formats.

CEC is the 'Consumer Electronics Control' protocol. CEC is transmitted on a one-wire connection on pin 13 of the HDMI connector with a data rate of 417 bit/s. It is intended to simplify the control of connected consumer devices ("one-touch-playback"). A Blu-Ray Player can control the connected display device, devices can switch each other on and off, etc. This can be very useful for the regular home setup with a few devices. As soon as a HDMI switcher or distribution is involved the advantages could turn to the opposite. For some devices the CEC cannot be switched off and easily wrong commands go to the wrong devices ..

The HDMI is built of four twisted and shielded pairs for video, audio and clock data, five single conductor wires and a cable pair for control data (DDC).

HDMI is backwards-compatible with DVI-D. All data of DVI can be transferred to HDMI, but by connecting HDMI to DVI, not all data is transmitted. And DVI doesn't carry any audio signals. HDMI supports HDCP (High-bandwidth Digital Content Protection), like DVI, to prevent copying of digital content.

HDMI is compatible with Displayport 1.1. Displayport is a licence-free format to connect computers and displays, specified in 2006.
A Displayport-to-HDMI adaptor can be used to connect a HDMI device to a Displayport output. With this adaptor the source device sends HDMI signals over the Displayport rather than Displayport signals. These adaptors operate only in one way, they cannot be used to connect HDMI to Displayport. To operate with HDMI compatibility the Displayport must be version DP++.
The maximum cable length for Displayport for a 2560 x 1600 (WQXGA) signal is two meters with a so-called 'DP Certified' cable.