This app is going to make a revolution in all domains of human interaction. Have fun!
Rationale of fair use for the use of the songs:
The sound samples come from commercial recording. Its inclusion here is claimed as fair use because:
It is samples of no more than 30 seconds from a much longer recording, and could not be used as a substitute for the original commercial recording or to recreate the original recording.
It is of a lower quality than the original recording.
It is not replaceable with an uncopyrighted or freely copyrighted sample of comparable educational value.
It is believed that this sample will not affect the value of the original work or limit the copyright holders rights or ability to distribute the original recording.
The audio sample is a copyrighted work. U.S. copyright laws apply to this work.