Standard Ports and Connections
Just as a good audio/video receiver will include a number of surround sound decoding schemes, the receiver is also likely to have a great variety of connection options and associated input and output ports. Many are now standardized, but the best receivers provide legacy support for older connection types as well as the most current, protected content digital streams such as Blu-ray video and audio over HDMI.
HDMI Inputs and Outputs
HDMI stands for High Definition Multimedia Interface. It's a standard interface for connecting components that carry media through protected streams, such as Blu-ray disc video. HDMI is necessary to support HDCP (high-bandwidth digital copy protection) and carries both high-definition video and the decoded audio streams.
It's best to have multiple HDMI inputs - at least one for every high-definition source that you plan to manage through the A/V receiver. Three HDMI inputs are acceptable, but a single HDMI input, for purposes of future expansion, is not a desirable feature.
A single HDMI output is most common for home theater A/V receivers, although some higher-end gear have two or more.
Composite, Component, and S-video
Composite video is the familiar connection to red, white, and yellow cables with RCA-type jacks that carries left and right audio and standard definition video. They are used to connect DVDs and VCRs, but are not used with high-definition digital streams.
Component video is similar to composite, but it uses three cables to carry the video - one for luminance and two for color (or chrominance). This was fashionable for a while, mainly with large wide-screen TVs, but the advent of HDMI has largely removed the need for component video.
S-video is an improvement on composite inputs. S-Video input is desired as it's the best way to get a good signal from a standard DVD player. S-video contains one conductor for luminance and one for color.
Since S-video is a common connection found on standard DVD players, it's good to have at least one input and one output on an A/V receiver. (The receiver, of course, will provide quick switching between your standard and high definition sources.)
Optical Digital Inputs and Outputs
Optical digital inputs and outputs require a fiber-optic cable. Also known as "Toslink," the advantage of this type of connection is that the signal is not affected by radio frequency or other electromagnetic interference.
Optical inputs are more commonly found on A/V receivers than optical outputs. This is because few home theater setups include any recording devices that have a Toslink input.
One or more optical digital inputs are desirable on an A/V receiver, but the optical digital output can be considered optional or unnecessary as the receiver itself should be the primary audio component in the system.
Low Level Inputs and Preamp Outputs
Also known as "Phono Inputs," low level inputs are used to connect devices such as phonographs. Preamp outputs are exactly the opposite of low level inputs - they provide a low level output suitable for connecting external amplifiers. A receiver may also have a separate preamp output for a powered subwoofer, but most receivers can drive the subwoofer directly.
Unless you plan to include a turntable in your system, you probably won't be using any low level input on your receiver. Likewise, the trend today is certainly not toward external amplifiers. The receivers themselves are powerful.
Next: Major Features and Conclusion