Based around open-source software, www.playdar.org is a system that, in theory, could sit on top of streaming music services such as Spotify, We7, Rhapsody and Pandora.

When a user wants to stream a track they already have remotely on their computer, such as in their iTunes folder, Playdar will play it instead.

The theory behind this is that it will save streaming music services money because they will not have to deliver streams for tracks users have stored locally.

This ...