Nowadays there are many possibilities to establish an infrastructure for the delivery and consumption of multimedia
content. In practice, however, several elements that cover these possibilities are often stand-alone systems and a big
picture how these elements relate or even fit together is not available. Therefore, MPEG-21 aims to provide an open
framework for multimedia delivery and consumption.
Due to the heterogeneity of the current terminal and network infrastructures, multimedia content needs to be adapted to
specific capabilities of these terminal and network devices. Furthermore, user preferences and user environment
characteristics must also be taken into consideration. The problem becomes even more complex by the diversity of
content types and content encoding formats. In order to meet this heterogeneity and to be applicable to different
coding formats the adaptation must be performed in a generic and interoperable way.
As a response to this problem and in the context of MPEG-21, we present an approach which uses XML to describe the
high-level structure of the resource in a generic way, i.e., how the resource is organized in layers or packets. For
this purpose a schema for XML based bitstream syntax descriptions (generic Bitstream Syntax Descriptions - gBSDs) has
been developed in a coding format independent way. Transformations of the resource are based on elementary manipulation
instructions formulated with respect to the gBSDs. These instructions have been separated from the gBSDs in order to
use the same descriptions for different adaptations, e.g., temporal scalability, SNR-scalability, and semantical
adaptations. In the MPEG-21 framework those adaptations can be steered for instance by the network capabilities and the
user preferences.
As a result, it becomes possible for resource format agnostic adaptation engines to transform bitstreams and associated
descriptions to meet the requirements based on the network conditions, device capabilities and user preferences.
To verify the concept we present the results of several experiments that have been conducted to evaluate the
functionality and feasibility of this approach. In the experiments especially data streams of encoded images in the
JPEG2000 format and video streams based on the MPEG-4 standard have been used. For evaluation of the coding efficiency,
we describe an approach to encode the gBSDs using the extensions of the MPEG-7 BiM format which are currently under
consideration for MPEG-7 BiM version 2. The results of this evaluation shows that binary-encoded gBSDs provides
interoperability in the adaptation chain and coding format independence of the adaptation engine by approximately 5% of
supplemental bandwidth when delivered with the resource.
The gBSD technology has been submitted as a response to the ISO/IEC JTC1/SC29/WG11 Call for Proposals on ISO/IEC
21000-7 (MPEG-21 Digital Item Adaptation), is part of ISO/IEC 21000-7 Committee Draft and ongoing experiments are
conducted especially to enhance the interoperability with other tools in the MPEG-21 framework.