This paper presents a transport layer design for the audio and video transmission application over the next-generation network,based on the existing Direct Show media framework, in which there are some work and breakthrough of network applications. The implement supports not only IPv4network but also for the forthcoming large-scale IPv6networks, with the IP layer protocol-independent transmission; using the RTP / RTCP transport mechanism controls the quality of the unique Direct Show network transmission service, and the fact that the media transmission of Direct Show is generally limited to the specific media format is pulled down, through the unique method of the audio and video head information transmission; meanwhile the design also can support multicast transmission. The theory and experiment show that a high-performance audio and video transmission system over the next-generation networks can be rapidly constructed via this design.