What function of HDMI allows one AV device to control another when connected via HDMI cables?

The function of HDMI that allows one AV device to control another when connected via HDMI cables is Consumer Electronics Control, commonly referred to as CEC. CEC is a feature that enables various HDMI devices, such as TVs, set-top boxes, and sound systems, to communicate and control each other using a single remote control. This is highly advantageous for simplifying user experience, as it reduces the need for multiple remote controls to operate different devices.

For instance, with CEC, a user can turn on the TV and have it automatically switch to the correct input for a connected Blu-ray player. Similarly, when the Blu-ray player is turned off, the TV can also be set to turn off. This level of interoperability enhances the convenience of managing multiple devices in an AV setup.

The other options, like Video Control and Audio Return Channel, do not pertain specifically to device control capabilities in the same way that CEC does. HDMI Link Control is not a widely recognized HDMI term and is not the correct terminology for this function, making CEC the clear correct choice.