Which of the following is NOT considered a user interface?

In the context of audio-visual systems, a user interface refers to any tool or device that allows a user to interact with or control a system. A remote control, touch panel, and joystick all serve this purpose by providing users with the means to send commands to the AV equipment. They enable direct manipulation and control of various functions such as volume adjustment, source selection, and playback control.

On the other hand, an encoder is primarily a device used to convert signals from one format to another, such as compressing video or audio formats for transmission over networks. While it plays a crucial role in the overall AV system by facilitating signal processing and transmission, it does not serve as a means for direct user interaction. This distinction is key in understanding why the encoder is not classified as a user interface.