A novel process and system for flexibly adding supplemental digital program content such as, for example, transactional advertising content, games, polls, contests, interactive music videos, and e-commerce content generally and the like, into pre-prepared digital media files, such as an MP3 audio file or the like, for playback by digital playback apparatus, wherein the pre--prepared media file is modified by embedding therein executable code representing such supplemental program content, and enabling the playback apparatus to decode and execute the presentation of the supplemental program material as an addition to the playback of the pre-prepared media file content.