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Publications of Wolfgang Effelsberg

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Konferenz Beitrag

  • Volker Hilt, Martin Mauve und Wolfgang Effelsberg. IEEE Computer Soc., 2001 A Light-Weight Repair Protocol for the Loss-Free Recording of MBone Sessions . Los Alamitos, Calif. [u.a.]With the increasing popularity of MBone conferences, the need arose to archive the multimedia streams of these conferences. Like all network applications, a conference recorder is subject to packet loss, which introduces gaps into recorded media streams. Such gaps degrade the playback quality of an archived media stream or even disable the correct playback. In this paper, we present a novel scheme for the loss-free recording of media streams. In contrast to existing systems that require the placement of recording caches within the network, our approach enables an end-to-end system design. We present a detailed protocol analysis that confirms the validity of our approach.
  • Volker Hilt, Martin Mauve, Jürgen Vogel und Wolfgang Effelsberg. ACM Order Dep., 2001 Interactive Media on Demand: Generic Recording and Replay of Interactive Media Streams . New York, NYIn this demonstration we present a generic recording service for distributed interactive media, i.e., media which allow a distributed group of users to interact with the medium itself. Typical examples of this media class are shared whiteboard systems, distributed virtual environments and networked computer games. By defining an abstract model and an application level protocol we were able to develop the first generic recording service for arbitrary distributed interactive media. This service is called Interactive Media on Demand (IMoD), and it is able to record and replay all applications that are based on the RTP/I protocol. In particular it allows random access to the recorded media streams. We demonstrate the IMoD system by recording and replaying a shared whiteboard, a networked computer game and a 3D telecooperation application.
  • Claudia Schremmer, Christoph Kuhmünch und Wolfgang Effelsberg. IEEE, 2001 Layered Wavelet Coding for Video . [Piscataway, NJ]Video coding for Internet applications faces major challenges. Due to the heterogeneity of the network, users with very different access bandwidths to the Internet want to be satisfied by the highest possible quality of their real-time application. A good coding scheme for layered video asks for maximization of the subjective visual quality at a given bandwidth, for scalability and coding complexity. In this article, we discuss and evaluate different policies for layered wavelet video coding. A heuristic of the actual bit rate originating from our implementation, the degree of scalability, and the visual quality of the coded video lead us to pronounce parameter setting recommendations.

Forschungs Papier

  • Claudia Schremmer, Christoph Esser, Christoph Kuhmünch und Wolfgang Effelsberg. , Technical report. 2001 A Wavelet Transform Applet for Interactive Learning Mannheim, . 01-004
    In recent years, new forms and techniques of teaching have appeared, based on the Internet and on multimedia applications. In the teleteaching Project Virtual University of the Upper Rhine Valley (VIROR), multimedia simulations and animations complement traditional teaching material. Lecturers use Java applets in their courses to explain complex structures. These are then stored in a multimedia database to enable asynchronous learning. The wavelet transform has become the most interesting new algorithm for still image compression. Yet, there are many parameters within a wavelet analysis and synthesis: choice of the wavelet filter bank, decomposition strategy, image boundary policy, quantization threshold, etc. We consider the wavelet transform to be a typical example of a complex, hard-to-understand algorithm that needs illustration by interactive multimedia. In this article, we present the didactic background and the implementation of a sample applet on the discrete wavelet transform, as taught in our multimedia course.