Service expected to launch beta later this year.

EMI Music has licensed its catalog to an experimental, ad-supported peer-to-peer file-sharing service from Qtrax.

Like other legitimate P2P networks that have come to market in the wake of the Grokster Supreme Court ruling, the Qtrax service limits copyrighted content to either paying monthly subscribers or those paying for song ala carte. In addition, Qtrax has added a free, ad-supported option that lets users download copyrighted music at no cost.

Such tracks are formatted with a proprietary technology that limits the number of times each can be played before the user must either buy the track or become a monthly subscriber. Like other ad-supported music service launched of late, the Qtrax model is designed to attract new users with free music while still paying rightholders via a share of the advertising revenue.

The Qtrax service is expected to launch as a public beta trial later this year. Audible Magic is providing the filtering technology.