We address the unique requirements of a multimedia file system such as continuous storage and retrieval of media, maintenance of synchronization between multiple media streams, and efficient manipulation of huge media objects. We present a model that relates disk and device characteristics to the recording rate, and derive storage granularity and scattering parameters that guarantee continuous access. In order for the file system to support multiple concurrent requests, we develop admission control algorithms for determining whether a new request can be accepted without violating the realtime constraints of any of the requests.We define a strand as an immutable sequence of continuously recorded media samples, and then present a multimedia rope abstraction which is a collection of individual media strands tied together by synchronization information. We devise operations for efficient manipulation of multi-stranded ropes, and develop an algorithm for maintaining the scattering parameter during editing so as to guarantee continuous playback of edited ropes.We have implemented a prototype multimedia file system, which serves as a testbed for experimenting with policies and algorithms for multimedia storage. We present our initial experiences with using the file system.

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Designing file systems for digital video and audio

A multimedia communication system includes both the communication protocols used to transport the real-time data and the distributed computing system (DCS) within which any applications using the protocols must execute. The architecture presented attempts to integrate these communications protocols with the DCS in a smooth fashion in order to ease the writing of multimedia applications. Two issues are identified as being essential to the success of this integration: the synchronization of related real-time data streams, and the management of heterogeneous multimedia hardware. The synchronization problem is tackled by defining explicit synchronization properties at the presentation level and by providing control and synchronization operations within the DCS which operate in terms of these properties. The heterogeneity problems are addressed by separating the data transport semantics (protocols themselves) from the control semantics (protocol interfaces). >

An architecture for real-time multimedia communication systems

MINOS is an object-oriented multimedia information system that provides integrated facilities for creating and managing complex multimedia objects In this paper the model for multimedia documents supported by MINOS and its implementation is described Described in particular are functions provided in MINOS that exploit the capabilities of a modern workstation equipped with image and voice input-output devices to accomplish an active multimedia document presentation and browsing within documents These functions are powerful enough to support a variety of office applications Also described are functions provided for the extraction of information from multimedia documents that exist in a large repository of information (multimedia document archiver) and functions that select and transform this information Facilities for information sharing among objects of the archiver are described; an interactive multimedia editor that is used for the extraction and interactive creation of new information is outlined; finally, a multimedia document formatter that is used to synthesize a new multimedia document from extracted and interactively generated information is presentedThis prototype system runs on a SUN-3 workstation running UNIX'" An Instavox, directly addressable, analog device is used to store voice segments

Multimedia document presentation, information extraction, and document formation in MINOS: a model and a system

This paper describes the design and initial implementation of the Rapport multimedia conferencing system, which supports interactive, real-time, distributed conferences among two or more users. Using computers connected by data and voice networks, this system creates an environment in which many sorts of meetings can take place, including telephone conversations, discussions among colleagues, and lectures. Rapport provides new opportunities for meetings, allowing a user to interact with distant colleagues and to participate in several conferences concurrently at his or her workstation. The system allows many existing computer programs to be used, unmodified, within its conferencing environment. Thus computer-generated data and displays are available to the conferees for manipulation and editing, enhancing the exchange of information during meetings. Although Rapport does not encourage a particular methodology of meeting conduct, such specialized support can be built using Rapport.The paper outlines Rapport's conference abstraction and the model on which it is based — the “virtual meeting room.” It then presents an overview of Rapport's architecture, discusses the system's environmental requirements, and concludes by mentioning some of our plans for future work with Rapport.

The rapport multimedia conferencing system

Groupware, like other forms of information technology, should be designed with the users’ needs and capabilities as the focus. User‐centered system design consists of observation and analysis of users at work, assistance in design from relevant aspects of theory, and iterative testing with users. We illustrate the various stages of this approach with our development of group ware for software designers. We have extensive studies of designers at work, have developed the beginnings of a theory of distributed cognition, and are at the first stages of iterative testing and redesign of a prototype of a shared editor to support their work.

User‐centered design of collaboration technology

object model as the basic system organizing principle. With this model, all system activity can be thought of as operations on a collection of objects managed by the system and organized into classes called types. Examples of object types are documents, processes, and folders. In its simplest terms, the IPC provides the communication primitives and mechanisms for delivering operations to objects and delivering the results, if any, of operations back to invoking clients. Some processes, called object managers, play a special role in implementing objects. The Document Manager and Authentication Manager are examples of managers. Generally, when an operation is invoked on an object, it is delivered to a manager for the object that performs the operation. Every object has a Unique Identifier (UID) that is a fixed-length, structured bit string. It includes fields that specify the object type and the host upon which the object was created, as well as fields that serve to ensure its uniqueness. Although, ultimately, all references to objects are through UIDs, some managers also support symbolic naming. For example, the folder hierarchy of the Document Store implements a symbolic name space by providing a mapping between user-defined symbolic names and object UIDs in order to facilitate user references to objects. The IPC is message oriented, and it supports object-oriented addressing. Operations invoked on objects are sent as messages addressed to the objects. That is, addresses for messages are object UIDs. The object addressed is the operand, and the message data contains the operation and any additional parameters necessary to specify the operation. The role of the IPC is to deliver the message to the manager for the object (a process), which can perform the operation requested. Responses are sent as messages from object managers to requesting clients. When sending a message, a process need not specify the host where the addressed object resides. To deliver the message, the IPC must determine the host. Certain object types are such that

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Diamond: A Multimedia Message System Built on Architecture