<title>Retrieval techniques for compressed video streams</title>

Abstract

A number of applications require audio and video data. Access to such data requires continuous real-time stream flow during playback (recording). This requires scheduling access to storage devices for such data. The high volume of such streams, especially video, makes it necessary to store them using compression schemes like JPEG and MPEG. However, doing so introduces playback data rate variability which in turn leads to poor storage system utilization if playback guarantees are to be maintained. Not all applications require perfect playback, and some tardiness and discontinuity during playback, within limits of acceptable Quality of Service (QoS), is tolerated. In this paper we briefly describe solutions to two problems that arise in scheduling the retrieval of compressed streams from secondary storage. Firstly, we propose QBSCAN, a scheme which reserves I/O bandwidth based on statistical estimates of playback rate in order to improve utilization. This is achieved by incorporating the QoS which comprises the playback rate (in frames per second), the maximum (consecutive) skipped frames, and the mean time between frame skips. Secondly, we develop storage techniques specifically designed for MPEG video, to be used in conjunction with QBSCAN, that allows robust playback. This is a problem because MPEG encoding introduces inter frame dependencies which make it hard to drop frames arbitrarily. Thus, the objectives of QBSCAN are to maximize the storage system utilization, and minimize buffer requirement, while providing the needed QoS despite data rate variability and dependency. Simulation studies are used to validate the efficacy of the proposed techniques.