Abstract: A new transport protocol called Audio-Video Protocol (AVP) for highly efficient multimedia communications on Internet is presented in this paper. While providing similar real-time delivery functions of RTP/RTCP, AVP adopts a novel audio-based synchronization scheme. This synchronization scheme has two advantages. One is that there is no need to include a timestamp in each transmitted packet so that the AVP header is small for highly efficient transmission. The other is that AVP can achieve lower end-to-end message delay by putting multiple audio frames or mixed audio-video frames in the same AVP packet to reduce the packet rate. Furthermore, AVP provides different QoS by assigning different priority numbers to the packets. Simulation results are presented to show the good performance of AVP in real-time video-audio delivery.