An interface device coupled between a computer system and a display system. The interface device includes a control module. The control module receives data from the computer system, and determines whether to display the data on the display system in a projection mode or in a media rendering mode according to operation signals inputted by a user. In the projection mode, the data includes static pictures. The control module projects the static pictures onto the display system in sequence. In the media rendering mode, the data includes a video stream. The control module controls the video stream to be transmitted from the computer system to the display system and controls the playback of the video stream on the display device. When in the projection mode and when the operation signal indicates that switching to the media rendering mode is required, the media rendering mode is activated in the projection mode.