title: 3GP/AMR mix/merge tracks
body: <p>Is there an easy way to merge 2 3gp (amr) audio files into a single audio file?</p>
  
  <p>I need them to be synchronous/over top of each other not one after the other.  I am using android to do this.  I have heard somewhere that for some audio formats you can simply add the bytes (being careful that you dont get a too high or too low result).  Is this true with the 3gp/amr format on android?</p>