A method and apparatus for transforming a description of an encoded bit stream is described. The encoded bit stream comprises data packets and the description is written in a markup language such as BSDL. A group of one or more data packets is described in the description by an element, the element having at least one attribute containing a transformation tag. The description is scanned to check for a transformation tag in accordance with a predetermined condition and an adapted description is generated. The transformation of multimedia files is described to provide for content scalability. The adaptation approach works as follows: instead of directly adapting the bit stream, the description of the bit stream is modified, by use of so-called style sheets. Therefore, from the modified description a binary form file can be generated.