Transmission end device

The invention provides a transmission end device which is suitable for being coupled with an image providing device and a receiving end device. The transmission end device comprises a first conversion unit, a second conversion unit, a wireless module and a processing unit. The first conversion unit is used for being coupled with an image providing device through an HDMI transmission line so as to receive a first video and audio stream provided by the image providing device. The second conversion unit is used for being coupled with the image providing device through the Type-C transmission line so as to receive a second video and audio stream provided by the image providing device. The wireless module is connected to the receiving end device in a wireless communication mode. The processing unit preferentially selects the first conversion unit to receive a first audio-video signal output by the first audio-video stream converted by the first conversion unit, and the processing unit transmits the first audio-vid