Qtrax, the ad-supported P2P music download service, has finally relaunched in the U.S., more than a year after it originally proposed to go live.

The subsidiary of Brilliant Technologies originally unveiled their service at the international music tradeshow Midem last year, but it quickly closed down after it turned out the company hadn't finalized the major label agreements it said it had. Since then, Qtrax has signed licensing deals with all four major labels, and a number of independents.

The service requires users to download a Web-based media player that lets users browse and play songs, as well as displays ads in return for free downloads. Songs downloaded are not compatible with the iPod or any Mac products at this time.

The Qtrax relaunch comes just weeks after another ad-supported music download service - SpiralFrog - closed down after it could not meet its debt obligations. The SpiralFrog situation has cast a shadow of doubt on the viability of ad-supported music download services at a time when ad-supported streaming services like imeem and Spotify are taking center stage.

The cost of licensing music to download is far greater than the cost of licensing music to stream on demand. Even the less expensive streaming services are facing financial hardships, as the rates the get from advertisers are not enough to cover the cost of their music licenses.

But Qtrax maintains its business model is different than SpiralFrog's. The former CEO of SpiralFrog-Robin Kent, who left the company a year before it went under-serves as an advisor for Qtrax. Jason Berman, former head of the RIAA and IFPI, leads its advisory board.

It plans an international launch in about a month.