Capo can open, play and analyze songs purchased from the iTunes Store as well as MP3, AIFF, WAV, M4A audio files. As with all apps, Capo cannot play music that is protected using Digital Rights Management (DRM) technology.
As soon as you add a song to Capo and start working on it, Capo will save your song as a Project. A Project contains a copy of the original song file, as well as the detected chords, beats, and key. Capo also stores the playback speed, regions, chord edits, and any other changes you made while working on the project.