Part 7 of MPEG-21 entitled Digital Item Adaptation (DIA), is an emerging metadata standard defining protocols and descriptions enabling content adaptation for a wide variety of networks and terminals, with attention to format-independent mechanisms. The descriptions standardized in DIA provide a standardized interface not only to a variety of format-specific adaptation engines, but also to format-independent adaptation engines for scalable bit-streams. A fully format-independent engine contains a decision-taking module operating in a media-type and context independent manner, cascaded with a bit-stream adaptation module that models the bit-stream adaptation process as an XML transformation operating on a high-level syntax description of the bit-stream, with parameters derived from decisions taken. In this paper, we describe the DIA descriptions and underlying mechanisms that enable such fully format-independent scalable bit-stream adaptation. Further, a new model-based, compact and lightweight transformation language for scalable bit-streams is described for use in the bit-stream adaptation module. Fully format-independent adaptation mechanisms lead to universal adaptation engines that substantially reduce adoption costs for new media types and formats because the same delivery and adaptation infrastructure can be used for different types of scalable media, including proprietary and encrypted content.