title: How to switch the android music output device
body: <p>I'm doing some test work on android music playback. I have a headset and a bluetooth headset connect with the phone at the same time. 
  Then there will be 4 output devices that can play the sound: <strong>speaker, handset, headset, and the BT_headset.</strong> 
  What I want to know is: is there a way to switch the audio output to the 4 device using code?
  I cant do switch between speaker and handset if there is no headset plugin using <strong>audioManager.setMode()</strong>. But, if a headset plugin the sound can not out from handset. 
  Then, if the headset and bt_headset connect at the same time, the sound always out from the later connect one.</p>