Adaptive systems for improved media streaming experience

Supporting streaming media applications over current packet network infrastructures represents a challenging task in many regards. For one, the lack of quality of service (QoS) guarantees in existing networks such as the Internet means that time-constrained media packets will face dynamic variations in bandwidth, loss rate, and delay as they traverse the network from the sender to the receiver. The variable rate of media traffic represents yet another difficulty when transmission constraints need to be met. Finally, the heterogeneity of client devices and access bandwidth coupled with custom user preferences exacerbate the problem of smooth and quality-optimized media playback even further. In this article we provide an overview of the various techniques for media and streaming strategy adaptation, which can be employed to deal with the difficulties imposed by such dynamic environments. These techniques depend on the characteristics of the media application, in particular on the network streaming infrastructure and the timing constraints imposed on the media packets´ delivery. We survey adaptation techniques that act on the encoding of the multimedia information, on the scheduling of the media packets, or that try to combat transmission errors. We also briefly overview some media-friendly networking solutions, which contribute to increased QoS by incorporating some level of intelligence in intermediate network nodes. Finally, we describe a few open challenges in media streaming, emphasizing strategies based on promising cross-layer approaches where adaptation strategies are applied in a coordinated manner, across different layers of the network protocol stack