A home theater system includes construction, presentation, and commerce in, songs. Presentation includes at least one of: metadata about songs or sounds, a function capable of transitioning from one song to a next song, and user preferences; and can determine in what manner to transition from one song to a next song. Construction of songs includes either factors above, or at least one of: a function or a user extension capable of selecting a next song, and an element capable of determining whether the song is perceptually random. A user interface is capable of searching playlists and selecting them for presentation, representing each playlist with a substantially unique pictorial representation, distinguishing in presentation between those playlists licensed to the user and those that are not, and capable of substantially immediate purchase of playlist licenses either individually or in bulk and either automatically or with minimal intervention.