R. Kelly wrote a song for a soundtrack.
Before the 1970s, soundtracks (with a few exceptions), accompanied towards musicals, and was an album that featured vocal and instrumental, (and instrumental versions of vocal songs) musical selections performed by cast members
 First conceived by movie companies as a promotional gimmick for new films, these commercially available recordings were labeled and advertised as "music from the original motion picture soundtrack", or "music from and inspired by the motion picture

