What Are HDMI Ports?

By David Lipscomb

High-definition multimedia interface ports are found on nearly all modern pieces of home theater gear. Without these ports and the attached electronics, the cables would be useless. Discussing what these ports do, and how their importance is critical to HDMI-based systems, is critical to understanding the process.

Output Function

HDMI ports send audio, video and control information to switchers, televisions, projectors and audio/video receivers. These devices also send the high-definition content protection (HDCP) key, which must be acknowledged at the other end of the cable.


HDMI is a two-way process that requires communication from sending to receiving device. As a result, the role the port plays on the input side of the signal is critically important. These ports are connected to the electronics that decode the incoming signal from the source component, verifying the HDCP handshake, and sending display data to the source. In addition, these ports must be able to pass along the HDCP coding, if there are other devices upstream.

Switching Devices

Connecting HDMI cables to multiple ports is useful to hook up multiple devices. Each source device carries its own audio and video stream, and has its own unique HDCP key. Therefore, unless the ports are linked to a switcher that can handle this, there may be a loss of signal. Switched HDMI ports are still sold even though many receivers have multiple HDMI switching inputs. This is due to the fact that most all new A/V devices are equipped with an HDMI output.

Legacy Devices

Older devices that only utilize component or S-video analog video cabling can be used with a scaler. This is a device that has analog ports on the input side and HDMI output ports on the other. Internally, the scaler takes this analog information and converts it to digital. This is known as transcoding. Additionally, digital video interface (DVI) systems are fully backwards-compatible with HDMI. In fact, the video sending portion is virtually identical. The difference is that the connector and port for DVI is larger, yet offers no provision for carrying audio.