The HDMI spec calls for three discrete channels, which are primarily used to carry three different kinds of data/signal: The DDC (display data channel) negotiates which audio/video formats are supported by the receiver, and is used for HDCP (content protection DRM); TMDS (transition minimized differential signaling) carries the actual audiovisual data; and CEC (consumer electronics control) is a channel that allows the user to control HDMI-connected devices via a universal remote, or alternatively allows HDMI devices to control the TV/other HDMI devices. (For example, Google Chromecast uses the CEC command One Touch Play to automatically switch to the Chromecast when it begins playback).