Rdio – the music startup from Janus Friis and Niklas Zennstrom of Kazaa and Skype fame – has revealed more details about its service. It compares people’s music collections to its own catalogue, then lets them stream the songs that match to any device, including web browsers and mobile phones. The service will cost $4.99 a month for web-only access, and $9.99 a month to include mobile access via iPhone, BlackBerry or Android handsets. It has deals with all four major labels as well as indie aggregators, and a catalogue of five million tracks. Social features are high in the mix too, with users able to listen to the collections of their friends.