HDMI Cables - The Basics


HDMI (High-Definition Multimedia Interface) is a compact audio/video interface for transmitting uncompressed digital data.  It represents a digital alternative to consumer analog standards, such as radio frequency (RF) coaxial cable, composite video, S-Video, SCART, component video, D-Terminal, or VGA. HDMI connects digital audio/video sources—such as set-top boxes, upconvert DVD players, HD DVD players, Blu-Ray™ Disc players, AVCHD camcorders, personal computers (PCs), video game consoles such as the PlayStation 3, Xbox 360, and AV receivers—to compatible digital audio devices, computer monitors, video projectors, and digital televisions.

HDMI cables support any uncompressed TV or PC video format, including standard, enhanced, and high-definition video; up to 8 channels of compressed or uncompressed digital audio; and a Consumer Electronics Control (CEC) connection. The CEC allows HDMI devices to control each other when necessary and allows the user to operate multiple devices with one remote control handset.  Because HDMI is electrically compatible with the signals used by Digital Visual Interface (DVI), no signal conversion is necessary, nor is there a loss of video quality when a DVI-to-HDMI adapter is used.  As an uncompressed connection, HDMI is independent of the various digital television standards used by individual devices, such as ATSC and DVB, as these are encapsulations of compressed MPEG video streams (which can be decoded and output as an uncompressed video stream on HDMI). The HDMI standard was not designed to include passing closed caption data (for example, subtitles) to the television for decoding.  As such, any closed caption stream has to be decoded and included as an image in the video stream(s) prior to transmission over an HDMI cable to be viewed on the DTV. This limits the caption style (even for digital captions) 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 sending an upscaled 720p/1080i format via HDMI to an HDTV has no method to pass Closed Captioning data so that the HDTV can decode as there is no line 21 VBI in that format.

HDMI products started shipping in late 2003. Over 850 consumer electronics and PC companies have adopted the HDMI specification (HDMI Adopters).  In Europe, either DVI-HDCP or HDMI is included in the HD ready in-store labeling specification for TV sets for HDTV, formulated by EICTA with SES Astra in 2005. HDMI began to appear on consumer HDTV camcorders and digital still cameras in 2006. Shipments of HDMI were expected to exceed that of DVI in 2008, driven primarily by the consumer electronics market.