Can you elaborate in more detail , what you want to do ?
If a headphone support bluetooth but MP3 player doesn;t then you really can not make that link. Headphone having bluetooth will always work slave , while master will be MP3 player , and this will be a one way communication where master will send data to slave (headphone), responsibility of headphone will be, whatever data is coming, it convert from digital to electromagnetic signal which human can heard.
Rahul