Description and adaptation of digital items can be performed in either binary levels or metadata levels, which are the abilities of MPEG-21 Digital Item Adaptation (DIA) tools. BIFS and LASeR are parts of MPEG-4 standard for describing multimedia scenes, which can be written in XML format and then be encoded into binary format for the consumption of MPEG-4 terminals. BIFS is a stable standard, but LASeR is an emerging standard that is newly developed for lightweight applications in constrained terminals. We present a method for automatic adaptation of scenes constructed on BIFS into those constructed on LASeR. We focus on automatic adaptation of real objects' sizes and other conversion rules by employing MPEG-21 DIA tools. The motivation of this paper is to enable a real-time transcoding from BIFS to LASeR so that MPEG-4 content authors can distribute their existing contents to mobile devices without the need of reauthoring according to the new standard, LASeR.