Supporting interactive scanning operations in VOD systems

Efficient support for interactive VCR-like operations in video-on-demand (VOD) systems is an important factor in making such systems commercially appealing. In this paper, we focus on a particular type of interactive operations; namely, fast forward and rewind with scanning. Conventional approaches to supporting scanning operations have significant shortcomings in terms of their network bandwidth and/or set-top box buffering requirements. We introduce an efficient method for supporting scanning operations which does not require any extra bandwidth beyond what is already allocated for the normal play-back operation. To support both forward and reverse scanning operations at several speedups, multiple, differently coded versions of a movie are stored at the VOD server. These versions include a "normal version" for the normal play-back operation and a "scan version" for every different speedup that has to be supported. A request for a scanning operation is serviced by switching to an appropriate version at the VOD server. Only one version is transported and decoded at a time. Each scanning version is produced by encoding a sample of the raw movie frames, so that when decoded and played back at the normal frame rate, this version gives a perceptual speedup in the motion picture. Our approach for providing scanning operations is integrated into a previously proposed framework for distributing archived MPEG-coded video streams.⁷ To incorporate interactive scanning operations in that framework, we investigate mechanisms for controlling the traffic envelopes of the scan versions during the encoding phase and we discuss the pre-processing steps needed to generate scan versions with a desired traffic envelope. We then discuss the storage requirements of the scan versions and the latency for switching from one version to another. Simple and effective ways to control this latency are presented. Finally, we discuss the implications of implementing our approach to both the server and the client.