Updated

snocap.bmpSan Francisco start-up Imeem, a Web site focused on letting users share music and other media playlists, has come out of nowhere.

It now boasts 16 million unique users a month, and grabbing enough attention that it needs to start protecting content owners. It will announce tomorrow a partnership with Snocap, another San Francisco company, to identify the music streamed at Imeem, so that Imeem can pay a share of ad revenue to music content owners.

Snocap’s technology gives each music track a unique signature, and can identify the music when it is uploaded by Imeem users. It then gives content owners a platform to dictate the terms of their music’s use — including the right to negotiate the ad revenue share they get when a track is streamed over Imeem.

The companies said the ad-sharing model is a first of its kind. It is significant because competing sites like Google’s YouTube are struggling to come to terms with content owners.

Snocap says its registry has three million tracks.

This is a significant turnaround for Imeem, which two years ago was working on a peer-to-peer product that didn’t go anywhere.

Much of the music on Imeem comes from independent artists. But it says it has partnered with Virgin Records, Nettwerk Records, SubPop Records, Beggars Group, Domino Records and Warner Independent Pictures.

Imeem’s founder Dalton Caldwell says the site is the fastest growing on the Web, citing Hitwise statistics.

Snocap’s already powers MySpace’s music store, however Snocap chief executive Rusty Rueff says the Imeem partnership takes things a step further. The Imeem deal lets any content owner stream their content online (MySpace allows downloads). The other difference is the ad-revenue share, letting users listen to the music for free.

The two companies have a common investor in Morgenthaler Ventures.