Priority-progress streaming for quality-adaptive multimedia

Abstract

The Internet's ubiquity amply motivates us to harness it for video distribution, however, its best-effort service model is in direct conflict with video's inherent timeliness requirements. Today, the Internet is unrivaled in its rich composition, consisting of an unparalleled assortment of networks and hosts. This richness is the result of an architecture that emphasizes interoperability over predictable performance. From the lowest levels, the Internet architecture prefers the best effort service model. We feel current solutions for media-streaming have yet to adequately address this conflict between timeliness and best-effort service.We propose that streaming-media solutions targetted at the Internet must fully embrace the notion of graceful degradation, they must be architected with the expectation that they operate within a continuum of service levels, adjusting quality-resource trade-offs as necessary to achieve timeliness requirements. In the context of the Internet, the continuum of service levels spans across a number oftime scales, ranging from sub-second timescales to timescales as long as months and years. We say sub-second timescales in relation to short-term dynamics such as network traffic and host workloads, while timescales of months and years relate to the continuous deployment of improving network, compute and storage infrastructure.We support our thesis with a proposal for a streaming model which we claim is simple enough to use end-to-end, yet expressive enough to tame the conflict between real-time and best-effort personalities of Internet streaming. The model is called Priority-Progress streaming. In this proposal, we will describe the main features of Priority-Progress streaming, which we have been implemented in a software-based streaming video system, called the Quasar pipeline.Our work is primarily concerned with the class of streaming applications. To prevent confusion, we now clarify the important distinction between streaming and other forms of distribution, namely download. For a video, we assume download is defined so that the transfer of the video must complete before the video is viewed. Transfer and viewing are temporally sequential. With this definition, it is a simple matter to employ Quality-adaptive video. One algorithm would be to deliver the entire video in the order from low to high quality components. The user may terminate the download early, and the incomplete video will automatically have as high quality as was possible. Thus, Quality-adaptive download can be implemented in an entirely best-effort, time-insensitive, fashion. On the other hand, we assume streaming means that the user views the video at the same time that the transfer occurs. Transfer and viewing are concurrent. There are timeliness requirements inherent in this definition, which can only be reconciled with best-effort delivery through a time-sensitive adaptive approach.