Richard Staehli

A Distributed Real-Time MPEG Video Audio Player

This paper presents the design, implementation and experimental analysis of a distributed, real-time MPEG video and audio player. The player is designed for use across the Internet, a shared environment with variable traffic and with great diversity in network bandwidth and host processing speed. We use a novel toolkit approach to build software feedback mechanisms for client/server synchronization, dynamic Quality-of-Service control, and system adaptiveness. Our experimental results show that the feedback mechanisms are effective, and that the player performs very well in the Internet environment.

A quality-of-service specification for multimedia presentations

The bandwidth limitations of multimedia systems force trade-offs between presentation-data fidelity and real-time performance. For example, digital video is commonly encoded with lossy compression to reduce bandwidth, and frames may be skipped during playback to maintain synchronization. These trade-offs depend on device performance and physical data representations that are hidden by a database system. If a multimedia database is to support digital video and other continuous media data types, we argue that the database should provide a quality-of-service (QOS) interface to allow application control of presentation timing and information-loss trade-offs. This paper proposes a data model for continuous media that preserves device and physical data independence. We show how to define formal QOS constraints from a specification of ideal presentation outputs. Our definition enables meaningful requests for endto-end service guarantees, while leaving the database system free to optimize resource management. We propose one set of QOS parameters that constitute a complete model for presentation error, and we show how this error model extends the opportunities for resource optimization.

Storage System Architectures for Continuous Media Data

Data storage systems are being called on to manage continuous media data types, such as digital audio and video. There is a demand by applications for “constrained-latency storage access” (CLSA) to such data: precisely scheduled delivery of data streams. We believe that anticipated quantitative improvements in processor and storage-device performance will not be sufficient for current data management architectures to meet CLSA requirements. The need for high-volume (but high-latency) storage devices, high-bandwidth access and predictable throughput rates mean that standard latency-masking techniques, such as buffering, are inadequate for the service demands of these applications. We examine the ways in which storage system architectures must change in order to provide CLSA on continuous media, taking into account operating system and network support as well as database management. Particular points we cover include changes in the form of requests and responses at the application-database and database-OS interfaces new kinds of abstractions and data independence that data mangement systems will need to supply, such as quality-of-service requests and mapping of domain events to OS events effects of CLSA demands on query optimization, planning and evaluation, including the need for accurate resource estimates and detailed schedules new information requirements for the database system, such as better characterizations of storage subsystem performance and application patterns.

Demonstrating the effect of software feedback on a distributed real-time MPEG video audio player

This paper presents the design, implementation and experimental analysis of a distributed, real-time MPEG video and audio player. The player is designed for use across the Internet, a shared environment with variable tra c and with great diversity in network bandwidth and host processing speed. We use a novel toolkit approach to build software feedback mechanisms for client/server synchronization, dynamic Quality-of-Service control, and system adaptiveness. Our experimental results show that the feedback mechanisms are e ective, and that the player performs very well in the Internet environment.

Constrained-latency storage access

A class of constrained-latency storage access (CLSA) applications that require both large amounts of storage and guarantees for short latencies are presented. A range of existing approaches to meeting the requirements of CLSA applications is surveyed. Their limitations indicate that the technology does not yet exist to support complex CLSA applications on general-purpose storage architectures. A variety of good solutions exists for meeting throughput and latency requirements for continuous media data, including dedication of resources, presequencing, and greedy prefetching. However, none of the current approaches supports the automatic anticipation of scripted data access as required for interactive editing and playback of video segments.<<ETX>>

Device and physical data independence for multimedia presentations

Multimedia computing promises access to any type of visual or aural medium through digital networks. But can a given multimedia document be effectively accessed everywhere? The presentation of data must adapt to both the available communications bandwidth and the output device resolution. Current multimedia systems assume that applications require the highest possible quality and handle resource overloads through ad hoc methods, such as video frame dropping. To support a variety of applications with lower quality requirements, we need both new standards for scalable data encoding and new techniques for communicating application quality requirements. This paper describes a new approach for specifying quality of service (QoS) requirements based on functionality rather than on data encoding and device capabilities. The potential of distributed multimedia computing can be achieved by offering device-independent and physicaldata-independent service interfaces. Logical data independence is also desirable, but we omit discussion of it here in the interest of brevity. Device and physicaldata independence are well known principles of database system design. In multimedia systems they have the following meaning:

Supporting Access to Stored Multimedia Data in Large Distributed Systems Work in Progress

The advent of multimedia applications that employ continuous media data, such as digital audio and video, will have a profound impact on file system design. Such applications often require extremely large amounts of storage as well as very high, real-time, access rates. These requirements already pose significant problems for current file system designs. The problems are compounded by the fact that many multimedia applications require synchronized access to multiple data streams (for example, coordinating audio and video output).