What Is an HDMI Port Used For?

By G.D. Palmer

Most computers, televisions and other pieces of audio-visual equipment now feature HDMI, or High Definition Multimedia Interface, ports. This compact interface transmits digital data between devices, handling both sound and video or still images. It can simplify some home theaters by eliminating extra analog cables. It also provides high definition images and clean, high-resolution audio that most analog specifications can't offer. However, HDMI does have some limitations.

Transmission Types

HDMI ports can transmit standard video, as well as high-definition video up to 2560x1600 pixels. HDMI also transmits 8-channel, 192kHz digital audio without compression, plus compressed formats like DTS and Dolby Digital. The newer 1.3 standard adds support for Dolby TrueHD, DTS-HD Master Audio and other lossless digital audio formats. HDMI also supports both standard and more brilliant color transmissions, including 10-, 12- and 16-bit RGB or YcbCr color depths.

Connector Types

While HDMI transmits both video and audio information over one cable, not all cables work the same way or fit the same ports. HDMI connectors come in five basic types. Type A has 19 pins and is 13.9 millimeters by 4.45 mm. Type B is larger, at 21.2 mm by 4.45 mm, and includes 29 pins for double the video bandwidth capacity of type A. It works best with very high resolution displays. Both type A and B connectors appear in the HDMI 1.0 specification. Type C, defined in the 1.3 specification, was developed for portable devices. This 10.42 by 2.42 mm device has 19 pins like a Type A connector, and works in the same devices when used with an adapter. Type D, another micro connector, appears in the 1.4 specification and measures 6.4 mm by 2.8 mm, with similar functionality to Type C. Type E, also defined in HDMI 1.4, specifically works in cars and other vehicles.

HDMI Versus Analog

Unlike analog connectors, HDMI suffers very little data loss when transmitting digital video and audio. At high resolutions, it provides a sharper picture and cleaner on-screen text. HDMI also allows two-way communication between the video source and destination, permitting devices to automatically configure themselves. Most analog connectors don't provide the same resolution and video quality as HDMI. One exception, the electrically-compatible DVI format, provides equivalent quality, but is hard to find on video components and high-definition televisions as of the year 2010.

Closed Captioning

HDMI does not produce captions for televisions and movies as easily as other formats do. Instead, this standard relies on a digital set-top box to decode the closed caption data and turn it into an image, which is then included in the video stream. This limits caption styles and formats. It also increases complexity for consumers, since not all set's top boxes decode captions the same way.

Considerations

The HDMI standard only requires manufacturers to support sRGB video at 8 bits per component and uncompressed PCM audio. Other formats, including high-definition audio and video, deep color and ethernet transmission, are optional. This results in a wide variety of HDMI cables and options, which can be confusing for consumers.