Architecture and performance of server-directed transcoding

Proxy-based transcoding adapts Web content to be a better match for client capabilities (such as screen size and color depth) and last-hop bandwidths. Traditional transcoding breaks the end-to-end model of the Web, because the proxy does not know the semantics of the content. Server-directed transcoding preserves end-to-end semantics while supporting aggressive content transformations.We show how server-directed transcoding can be integrated into the HTTP protocol and into the implementation of a proxy. We discuss several useful transformations for image content, and present measurements of the performance impacts. Our results demonstrate that server-directed transcoding is a natural extension to HTTP, can be implemented without great complexity, and can provide good performance when carefully implemented.