A video device to generate analog video signals to a plurality of display devices comprises a video processing chip, a plurality of video output interface circuits and a plurality of detection circuits. The video processing chip converts input video data into the analog video signals and comprises at least one video decoder and a plurality of analog to digital convertors. The video output interface circuit transmits the analog video signals to the plurality of display devices. The detection circuit detects voltage of horizontal sync signals of the analog video signals to determine connection of the video output interface circuit to the display device, and generates a feedback signal to the video processing chip to control the video decoder and the analog to digital convertor accordingly.