MPEG-21 BSDL: a standardized adaptation framework for the customization of scalable bitstreams in the XML domain
The MPEG-21 Bitstream Syntax Description Language (MPEG-21 BSDL) specification is a part of the Digital Item Adaptation (MPEG-21 DIA, [1]) standard, which is in its turn embedded in the MPEG-21 Multimedia Framework [2]. MPEG-21 BSDL is a tool or language to describe the high-level structure of (scalable) bitstreams in XML documents. By using these XML descriptions (which are called Bitstream Syntax Descriptions or BSDs), the focus of a subsequent adaptation process is shifted from the compressed domain to the XML domain. By using the MPEG-21 BSDL framework, the BSDs enable the development of a format-agnostic adaptation engine for (scalable) bitstreams.
The idea behind BSDL is to develop format-agnostic conversion tools between bitstreams and their corresponding high-level XML descriptions, and vice versa.
MPEG-21 BSDL is a language built on top of the World Wide Web Consortium's (W3C) XML Schema language [3]. BSDL defines a number of restrictions on and extensions to XML Schema, which are fixed in the DIA specification. The entire data flow of the MPEG-21 BSDL framework is shown in Figure 1.
(1) The high-level structure of the coding format used is represented by a Bitstream Syntax Schema (BS Schema). The language used to construct such a BS Schema is BSDL, and this language is standardized in the DIA specification.
(2) The XML-based BSD of the scalable bitstream is generated by a format-agnostic parser once the original (encoded) bitstream and a corresponding BS Schema are known. The functioning of this parser, i.e., the BintoBSD Parser, is also defined in the standard.
(3)
The BSD can subsequently be transformed by using a well-known XML transformation technology like eXtensible Stylesheet Language Transformations (XSLT) or Streaming Transformations for XML (STX). This transformation represents the adaptation process in the XML domain.
(4)
The format-agnostic BSDtoBin Parser creates an adapted bitstream, using the transformed BSD, a corresponding BS Schema, and the original (scalable) bitstream.
Note that the employment of format-agnostic parsers (in particular, BintoBSD and BSDtoBin) means that the code base of these parsers does not have to be rewritten in order to support the customization of bitstreams compliant wih other coding formats.
On this webiste, we will show a number of samples of BS Schemata in order to generate BSDs for contemporary video coding specifications such as the scalable extensions on H.264/AVC.
References:
[1] ISO/IEC 21000-7:2004 Information technology -- Multimedia Framework (MPEG-21) -- Part 7: Digital Item Adaptation, 2004.
[2] I. S. Burnett, F. Pereira, R. Van de Walle, and R. Koenen, the editors. The MPEG-21 Book, Wiley, John & Sons, Inc, 2006.
[3] XML Schema part 0: Primer. Available from: http://www.w3c.org/TR/xmlschema-0, May 2001.
[4] G. Panis, A. Hutter, J. Heuer, H. Hellwagner, H. Kosch, C. Timmerer, S. Devillers, M. Amielh. Bitstream syntax description: a tool for multimedia resource adaptation within MPEG-21. Signal Processing: Image Communication 18(8) (2003) 721-747.