 relative importance of Internet media transmission must adapt to changing net- packets and their mutual dependencies, audio or video work characteristics; it must be network adaptive. It quality can be greatly improved. should also be media aware, SO that adaptation to changing The media server can implement intelligent transport network conditions can be performed intelligently. by sending the right packets at the right time, but the A typical streaming media system comprises four computational resources available for each media stream major components that should be designed and opti- are often limited because a large number of streams must mized in concert: be served simultaneously. Much of the burden of an ef- ficient and robust system is therefore on the encoder 1. The encoder application compresses video and audio application, which, however, cannot adapt to the varying signals and uploads them to the media server. channel conditions and must rely on the media server for 2. The media server stores the compressed media this task. Rate scalable representations are therefore streams and transmits them on demand, often serv- desirable to facilitate adaptation to varying network ing hundreds of clients simultaneously. throughput without requiring computation at the media 3. The transport mechanism delivers media packets server. Switching among bit streams encoded at different from the server to the client for the best possible user rates is an easy way to achieve this task, and this method experience, while sharing network resources fairly is widely used in commercial systems. Embedded scal- with other users. able representations are more elegant and are preferable, if the rate-distortion penalty often associated with scal- 4. The client application decompresses and renders the able coding can be kept small. video and audio packets and implements the inter- Section 3.5.2 begins with a review of the framework for active user controls. rate-distortion optimized (RaDiO) media streaming ini- The streaming media cli