code: function() {
        if(!volume) {
          return;
        } else if (volume.muted) {
          p.unmute(function(err, status) {
            if (err) return;
            volume = status;
          });
        } else {
          p.mute(function(err, status) {
            if (err) return;
            volume = status;
          });
        }
      }
docs: toggle between mute / unmute