Load an External MP3 File (not in Assets folder) - YouTube
Load Mp3 Music - Microsoft Apps
GainDemo on Android, .mp3: Unable to load file - Android - JUCE
GitHub - r2123b/Load-Mp3-into-Audioclip: instead of UnityEngine.WWW class, load .mp3 file by NLayer, which is cross platforms (Windows, Mac OS, Android, and iOS)