In order for the Media Server to play a file you need to send a Play signal, where you specify the URL of the file to be played. If the file is local then the URL format will be file://path_to_file/filename.wav; otherwise if the file is hosted remotely then the URL format will be http://something/filename.wav.
Upon receiving the Play request, the Media Server will ask the underlying AudioPlayer to process the URL, first guaranteeing that it is not malformed and that the file type is supported: .wav, .gsm, .tone, .mov, .mp4, .3gp. If all is fine, the player will open a stream to the file right away.
Finally, the AudioPlayer is activated so it can start processing the file and transmitting audio to the remote peer.
You can find a fully detailed discussion about this topic in the mobicents public forum as well (including links to github code):
https://groups.google.com/d/msg/mobicents-public/4zuUOM3zHsM/fQM6o80JEXwJ
Let me know if this helps.
Regards.