This letter describes a file format designed for interactive music service where users are able to recompose music based on their own preferences. The proposed design utilizes the flexible features of the ISO base media file format (ISO/IEC 14496-12, ISO-BMFF). The techniques offered in the proposed file format enable compact storage and efficient preset management, allowing users to recompose music with ease and convenience. Additionally, an implementation scheme for an interactive music player is shown along with its results.