Opus is a rather new codec that has better performance in terms of quality per bitrate than MP3 or Vorbis and it's open and royalty-free.
Android can play it since Android 5, but my native CyanogenMod CM12.1 Music player doesn't recognize the .opus files. Even if I rename them as .ogg they are skipped and it won't list them. If I force the music player to play them, it does play but in a kind of simple popup screen.
Is there a music player for Android that is open source and can play and list Opus files?