. The design and implementation of a continuous media player for Unix workstations is described. The player can play synchronized digital video and audio read from a file server. The system architecture and results of preliminary performance experiments are presented. 1. Introduction Our goal is to develop a portable user interface and continuous media support library that can be used to implement a variety of multimedia applications (e.g., hypermedia systems, video conferencing, multimedia presentation systems, etc.). A key component of these applications is a continuous media (CM) player that can play scripts composed of one or more synchronized data streams. Example data streams are: digitized video or audio, animation sequences, image sequences, and text. The initial application we are implementing to test our abstractions is a video browser that allows a user to play high quality videos stored in a large database on a shared file server. Figure 1 shows a screen dump of the brows...

The error handling method in traditional communication protocols is error detection and retransmission. This method is inappropriate for distributed multimedia systems for two reasons: It introduces variable delay unacceptable for isochronous streams, and it is very inefficient and difficult to use in the multicast environment typical for many multimedia applications. We propose AdFEC, an adaptable Forward Error Correction scheme based on binary polynomial algebra. It produces an adaptable amount of redundancy allowing different packet types to be protected according to their importance. The scheme was implemented in the framework of the XMovie project and proved to be very efficient. Permanent address: Praktische Informatik IV, University of Mannheim, 68131 Mannheim, Germany y Permanent address: Fachhochschule Gieen-Friedberg, Wilhelm-Leuschner-Str. 13, 61169 Friedberg 1 Introduction Two different approaches can be used to correct transmission errors in computer networks: ...

Digital movie systems offer great perspectives for multimedia applications. But the large amounts of data involved and the demand for isochronous transmission and playback are also great challenges for the designers of a new generation of file systems, database systems, operating systems, window systems, video encoder/decoders and networks. Today's research prototypes of digital movie systems suffer from severe performance bottlenecks, resulting in small movie windows, low frame rates or bad image quality (or all of these). We consider the performance problem to be the most important problem with digital movie systems, preventing their widespread use today. In this paper we address performance issues of digital movie systems from a practical perspective. We report on performance experience gained with the XMovie system, and on new algorithms and protocols to overcome some of these bottlenecks.

In this paper we describe the tool{supported speci- cation and implementation of a multimedia communication protocol on parallel hardware. MCAM is an application layer protocol for movie control, access and management. We specify the full MCAM protocol together with ISO presentation and session layers in Estelle. Using a code generator, we derive parallel C code from the speci cation. The code is compiled and executed on a multiprocessor system under OSF/1 and on UNIX workstations. Measurements show the performance speedup gained by several dierent con gurations of parallel units. We also report on experiences with our methodology.

Typical color video adapters of today's PCs and workstations use 8 bits per pixel as an index into the color lookup table (CLUT). Full color pictures and movies have to be reduced to 256 colors. In order to avoid false colors between two frames of a digital movie, a novel technique for computing the CLUT's is proposed: A subset of the CLUT entries is reserved for new colors of the next frame. The paper presents an algorithm for the gradual adaption of the color lookup table during the transmission of a movie. First experience is reported in the framework of the XMovie project. 1

Multimedia applications require a compression and decompression scheme for digital video. The standardized and widely used techniques JPEG and MPEG provide very good compression ratios, but are computationally quite complex and demanding. We propose to use an extension to the much simpler Color Cell Compression scheme as an alternative. Our extension includes the use of variable block sizes, the reuse of color index values from previously encoded blocks, and Huffman encoding of the stream of blocks. We present experimental results showing that our scheme provides much better runtime performance than MPEG, at the cost of a slightly inferior compression ratio. It is thus especially suited for software videos in high-speed networks.