A video conferencing system is disclosed. The video conferencing system includes a transmitter and a receiver. When the transmitter is coupled to a port of an information processing apparatus, the transmitter communicates with the information processing apparatus to determine whether the port of the information processing apparatus has video output function. When the above determination result is no, the transmitter emits a wireless signal. The transmitter is coupled to a display apparatus and used to receive the wireless signal and provide a default warning message to the display apparatus.