code: function add(track, playbackSuccess, playbackError, statusChange, progressChange) {
          if (!track.url) {
              console.log('ionic-audio: missing track url');
              return;
          }
  
          angular.extend(track, {
              onSuccess: playbackSuccess,
              onError: playbackError,
              onStatusChange: statusChange,
              onProgress: progressChange,
              status: 0,
              duration: -1,
              progress: 0
          });
  
          if (find(track)) {
              return track.id;
          }
  
          track.id  = tracks.push(track) - 1;
          return track.id;
      }
docs: /*
  Creates a new Media from a track object
  
  var track = {
  url: 'https://s3.amazonaws.com/ionic-audio/Message+in+a+bottle.mp3',
  artist: 'The Police',
  title: 'Message in a bottle',
  art: 'img/The_Police_Greatest_Hits.jpg'
  }