An optimized MPEG-21 BSDL framework for the adaptation of scalable bitstreams

A format-agnostic framework for content adaptation allows reaching a maximum number of users in heterogeneous multimedia environments. Such a framework typically relies on the use of scalable bitstreams. In this paper, we investigate the use of bitstreams compliant with the scalable extension of the H.264/MPEG-4 AVC standard in a format-independent framework for content adaptation. These bitstreams are scalable along the temporal, spatial, and SNR axis. To adapt these bitstreams, a format-independent adaptation engine is employed, driven by the MPEG-21 Bitstream Syntax Description Language (BSDL). MPEG-21 BSDL is a specification that allows generating high-level XML descriptions of the structure of a scalable bitstream. As such, the complexity of the adaptation of scalable bitstreams can be moved to the XML domain. Unfortunately, the current version of MPEG-21 BSDL cannot be used to describe the structure of large video bitstreams because the bitstream parsing process is characterized by an increasing memory consumption and a decreasing description generation speed. Therefore, in this paper, we describe a number of extensions to the MPEG-21 BSDL specification that make it possible to optimize the processing of bitstreams. Moreover, we also introduce a number of additional extensions necessary to describe the structure of scalable H.264/AVC bitstreams. Our performance analysis demonstrates that our extensions enable the bitstream parsing process to translate the structure of the scalable bitstreams into an XML document multiple times faster. Further, a constant and low memory consumption is obtained during the bitstream parsing process.