One of the many requirements of webcasters is that they don’t exceed the Sound Recording Performance Complement, which is defined in the law as…
(7) The `sound recording performance complement' is the transmission during any 3-hour period, on a particular channel used by a transmitting entity, of no more than-- ``(A) 3 different selections of sound recordings from any one phonorecord lawfully distributed for public performance or sale in the United States, if no more than 2 such selections are transmitted consecutively; or ``(B) 4 different selections of sound recordings-- ``(i) by the same featured recording artist; or ``(ii) from any set or compilation of phonorecords lawfully distributed together as a unit for public performance or sale in the United States, if no more than three such selections are transmitted consecutively: Provided, That the transmission of selections in excess of the numerical limits provided for in clauses (A) and (B) from multiple phonorecords shall nonetheless qualify as a sound recording performance complement if the programming of the multiple phonorecords was not willfully intended to avoid the numerical limitations prescribed in such clauses.
Our short version of this is that in a three-hour period the station can transmit no more than:
1) three songs from one album or compact disc, if no more than two of these are played in a row; or
2) four songs by the same featured artist or from the same box set, if no more than three of these are played in a row.