Efficient management of transcoding and multicasting multimedia streams

Management of multimedia applications is a very challenging task. This is especially true in the emerging new Internet where users use devices such as smart phones and PDAs, a considerable amount of them are connected via wireless connections, and peer to peer applications are becoming more and more popular. In this new environment, the multimedia format that should be sent to different users varies considerably and sending a media stream to a set of users often involves transcoding of formats. This paper addresses the problem of managing multicast streaming in this new environment by defining a framework in which transcoding can be done in internal network nodes, and not necessarily at the sender´s or at the receivers´ ends. In this framework the sender retrieves all the information regarding the transcoding abilities of the various nodes and the characteristics of the links. Then, it needs to decide how to broadcast the multimedia stream, in what formats, and where to perform the needed transcoding. We show that this algorithmic problem is NP-hard (and also hard to approximate). However, for the very practical case where the number of relevant formats is small, we present an efficient approximation scheme. We study, using simulations, the actual performance of our algorithm and compare it to transcoding at the sender´s or at the receivers´ ends. Our results indicate that performing transcoding in intermediate nodes is indeed efficient, and that our algorithm can find a much better streaming scheme than any known algorithm.