|< Contents ERCIM News No. 62, July 2005
SPECIAL THEME: Multimedia Informatics
ADMITS: Adaptation in Distributed Multimedia IT Systems
by Laszlo Böszörmenyi
The ADMITS project, at the Institute of Information Technology of the University of Klagenfurt (ITEC), has developed an experimental distributed multimedia system for investigations in adaptation, an increasingly important tool for resource and media management in distributed multimedia systems.
In recent years, a large number of papers have been published on the subject of adaptation in multimedia systems. These papers reflect a diversity of interpretations, however, generally have a rather limited scope. Best-effort scheduling and worst-case reservation of resources are two extreme cases, neither being well suited to cope with large-scale, dynamic multimedia systems. A middle course can be found in a system that dynamically adapts its data, resource requirements, and processing components to achieve user satisfaction. Nevertheless, there is no agreement about the questions of where, when, what and who should adapt.
A distributed multimedia system comprises several types of components, such as media servers, meta-databases, proxies, routers and clients. In addition, a large number of adaptation possibilities exist, from simple frame dropping up to virtual server systems that dynamically allocate new resources on demand. The main problem is determining which kind of component can best be used for each kind of adaptation.
In the frame of the ADMITS project, we are seeking answers to exactly this basic question, and to a number of related questions. In building the experimental system, we explore a number of possible adaptation entities (server, proxy, clients, routers), and implement and evaluate different algorithms for media, component and application-level adaptations. Experimental data is also collected in order to gain insight into when, where and how to adapt, as well as how individual, distributed adaptation steps interoperate and interact with each other. The overall architecture of the experimental system is depicted in the Figure.
|The Experimental Distributed Multimedia System.
The individual components play different roles in the adaptation process. They are connected physically by the network, and semantically by MPEG-7 Multimedia Descriptions and MPEG-21 DIA Descriptions that flow over the network. The reliance on these international standards makes the components interoperable with any standard-compliant components developed elsewhere. To our knowledge there exists no other system that handles adaptation in such a comprehensive and interoperable way.
Since ADMITS is a research project, its main emphasis is on the publication of papers. A list of these can be found on the home page of ITEC (http://www.ifi.uni-klu.ac.at/ITEC/), under Publications. However, in order to validate our ideas, but also with the aim of future industrial applicability, a large repository of software tools (called ViTooKi, for Video Toolkit) has been developed. The software tools are highly interoperable and available as open-source software (http://vitooki.sourceforge.net/). The repository is unique in providing a very rich set of interoperable video tools. The following non-exhaustive list gives an overview of the tools and their major features:
- Media server:
- standard compliant media streaming by using RTSP and RTP/UDP
- streams all media formats supported by the ffmpeg library (eg MPEG-1, MPEG-2, MPEG-4)
- communicates terminal capabilities of the client device and user preferences using standardized MPEG-21 descriptors
- supports real-time adaptation of media content according to the clients terminal capabilities, the user preferences, and the available network resources; for example, mobile devices get a lower stream quality than high-performance workstations with good network access
- implements standardized RTP extensions to allow intelligent retransmission of lost video frames where necessary
- can be run in a distributed environment that supports proactive service and content replication and migration operations; this is especially helpful when content adaptation steps are not allowed due to legal constraints or the user insists on the original stream in its full quality
- supports proactive adaptations by actively measuring and forecasting available server and network resources on and between server nodes.
- Proxy server:
- incorporates both a server and a client implementation (since a proxy must act as a server to the client and a client to the server)
- caches elementary streams in different quality versions
- implements quality-aware replacement strategies
- can be dynamically relocated in the vicinity of requesting clients.
- multimedia database schema based on the MPEG-7 standard
- multimedia indexing framework
- cost-based query optimization for range and k-nearest neighbour searches
- application-level libraries for content-based image retrieval systems, audio recognition tools, video browsing tools, and quality aware MPEG-4 proxies.
- Media player:
- standard compliant control of RTP-based media streams by using RTSP
- supports parallel presentation of many videos in different viewers, in different qualities
- implements a general framework for SMIL- and BIFS-based multi-scene presentations.
One of the most important and unique characteristics of the ADMITS project is the consequent combination of fundamental research with international standards. To reach this goal, ITEC has decided to participate in the standardization processes of the Moving Picture Experts Group (MPEG), especially in the area of MPEG-7 and MPEG-21. A number of contributions in the context of Digital Item Adaptation (DIA) have been submitted by ITEC (in partial collaboration with Siemens AG) and accepted by MPEG in the recent years.
Laszlo Böszörmenyi, Institute of Information Technology (ITEC), Klagenfurt University, Austria
Tel: +43 463 2700 3611