A study on transcoding of MPEG-4 BIFS scenes to MPEG-4 LASeR scenes in MPEG-21 digital item adaptation framework

Abstract

The MPEG-4 BIFS and MPEG-4 LASeR are parts of MPEG-4 standard for describing multimedia scenes in binary format. Scenes are multimedia presentations consisting of text, graphics, animation and real contents such as images, videos, and audios. BIFS and LASeR scenes can be written in XML format and then be encoded into binary format for the consumption of MPEG-4 terminals. While BIFS is a stable standard, LASeR is an emerging standard that is being newly developed for the purpose of lightweight applications in constrained terminals such as mobile phones. This explains why the LASeR specification is much simpler than that of BIFS. This thesis presents a method of transcoding for converting BIFS XML format into LASeR XML format. Analysis is conducted on the differences between BIFS and LASeR specifications and a set of mapping rules is proposed for the conversion purpose. The transcoding is done using an XSLT processor for converting the BIFS XML formats into the corresponding LASeR XML formats. The text to text conversion is incorporated into our transcoding system that also adapts real objects in the scenes such as images and videos. To enable MPEG-4 scenes to be accessed by mobile users in a transparent network, the transcoding scheme is implemented in MPEG-21 multimedia framework. MPEG-21 Digital Item Adaptation (DIA) tool is employed for enabling automatic adaptation of real objects and conversion rules according to terminal types, user preferences, and network condition. The motivation of the research in this this thesis is to allow the possibility of transcoding from BIFS to LASeR automatically. This would help MPEG-4 content authors to distribute their existing contents to mobile devices without the need of reauthoring and learning of a new standard.