Complex sentence: At the end of 1999, MP3.com launched a promotion called "Pay for Play," or P4P, involving an algorithm to pay each MP3.com artist on the basis of the number of streams and downloads of their songs.
Split into simpler sentences: At the end of 1999, MP3.com launched a promotion that allowed these artists to monetize their content on the site. Called "Pay for Play," or P4P, it used an algorithm to pay each MP3.com artist on the basis of the number of streams and downloads of their songs.