Coming hot off the heels of the recent Steam Discovery Update, Valve has brought the Steam Music Player out of BETA - complete with a few highly desired changes. Among these changes is the ability to finally listen to music that isn't part of Valve's database, as well as the ability to automatically have any soundtracks that are linked to your steam library added to your music library.
This move is yet another example of how the Bellvue-based company has been working to secure a spot for Steam in various other digital entertainment industries - not just Videogames, but also digital movies, professional software; and now music. That being said - this Steam extension definitely has a long way to go. Currently only MP3 files are supported, and there is no ETA in regards to when FLAC, OGG, or M4A support may be added.
Regardless; Valve is giving away free copies of their games OST's, and it is now loads easier to buy the soundtrack for a game you enjoy. Whether or not Steam becomes a popular outlet for purchasing music or any other media is yet to be seen, but the option is now there for those that may be interested.