API PlayMusic

Plays the given mp3 file. /script PlaySoundFile(soundFile);

Arguments

 * soundFile : String - path to a MP3 file. You can refer to both files in WoW's MPQs, or your own music files in your addon's directory.

Example
/script PlaySoundFile("Sound/Music/ZoneMusic/CavernsOfTime/CT_HyjalExtWalkUni06.mp3" )

Result
Current music fades out, login or custom music plays.