Not too long ago I setup my Owncloud and was playing with the music player feature, well cool.  While uploading an album I noticed that all the songs were group under a folder call unknown.  Did a little searching and found a fix on GitHub

Check it.

5.04: had to change
"public $option_max_2gb_check = null;"
in "3rdparty/getid3/getid3.php" to 
"public $option_max_2gb_check = false;"
else music shows one artist (unknown) with only unknown albums/tracks.

credit to Bobol  https://github.com/owncloud/core/issues/3084