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Unformatted text preview: IEEE TRANSACTIONS ON MULTIMEDIA, VOL. 1, NO. 2, JUNE 1999 217 Real-Time Interactive MPEG-4 System Encoder Using a Cluster of Workstations Yong He, Student Member, IEEE, Ishfaq Ahmad, Member, IEEE, and Ming L. Liou, Fellow, IEEE Abstract MPEG-4 currently being finalized by the Moving Pictures Experts Group of the ISO is a multimedia standard. MPEG-4 aims to support content-based coding of audio, text, image, and video (synthetic and natural) data, multiplexing of coded data, as well as composition and representation of audio- visual scenes. One of the most critical components of an MPEG-4 environment is the system encoder. An MPEG-4 scene may contain several audio and video objects, images, and text, each of which must be encoded individually and then multiplexed to form the system bitstream. Due to its flexible features, object-based nature, and provision for user interaction, MPEG-4 encoder is highly suitable for a software-based implementation. A full-scale software-based MPEG-4 system encoder with real-time encoding speed is a nontrivial task and requires massive computation. We have built such an encoder using a cluster of workstations collec- tively working as a virtual parallel machine. Parallel processing of MPEG-4 encoder needs to be carried out carefully as objects may appear or disappear dynamically in a scene. In addition, objects may be synchronized with each other. User interactions may also prohibit a straightforward parallelization. We pro- pose a modeling methodology that captures the spatio-temporal relationship between various objects and user interaction. We then propose a number of scheduling algorithms that periodi- cally allocate MPEG-4 objects to multiple workstations ensuring load balancing and synchronization requirements among multiple objects. Each scheduling algorithm has its own performance and complexity characteristics. The experimental results, while showing real-time encoding rates, exhibit tradeoffs between load balancing, scheduling overhead cost, and global performance. Index Terms MPEG-4, parallel processing, petri nets, sched- uling algorithm, video compression. I. INTRODUCTION A UDIO-VISUAL standards are required to enable the in- terfacing of various technologies. MPEG-4, currently be- ing developed by the Moving Pictures Experts Group (MPEG) of ISO and to be finalized by early 1999, will become the standard of multimedia [1]. The aim of MPEG-4 is to define a standard syntax and interfacing for technologies in computer, telecommunication, and television/film industries. MPEG-4 will support content-based communication, access, and ma- nipulation of digital audio-visual objects. In addition, MPEG-4 Manuscript received September 3, 1998; revised February 24, 1999. This work was supported by the Hong Kong Telecom Institute of Information Technology and the Research Grants Council of the Hong Kong Special Administrative Region. The associate editor coordinating the review of this paper and approving it for publication was Prof. Jan-Ming Ho.paper and approving it for publication was Prof....
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