Independence FM is a custom radio station in the PC version of Grand Theft Auto IV and the iPhone/iPod Touch version of Grand Theft Auto: Chinatown Wars.
Grand Theft Auto IV
In GTA IV, Independence FM works in the same way as custom radio stations in previous games, whereby music is placed in a directory (My Documents\Rockstar Games\GTA IV\User Music) and can then be heard in-game. It is accessed in the same way as other radio stations, and simply appears when the player scrolls through.
The player is given the option of playing the songs in order of the song titles or in random, or set Independence FM as a functional radio station, complete with a DJ (Gary Sheen), imaging voices and commercials between music tracks.
In order to play, songs must be free of any DRM restrictions. The game "knows" whether it has a DRM or not by checking whether the MP3 file has a "tag" within its coding that indicates a DRM restriction or otherwise.
Grand Theft Auto: Chinatown Wars
The iPhone/iPod Touch version of GTA Chinatown Wars introduces a similarly named Independence FM station for custom music tracks. As of the version 1.0.1, players must create an iTunes playlist titled "GTA", assigning the playlist to the game and allowing the game to randomly play songs within the playlist.