howler.js

/*!
 *  howler.js v1.1.11
 *  howlerjs.com
 *
 *  (c) 2013, James Simpson of GoldFire Studios
 *  goldfirestudios.com
 *
 *  MIT License
 */

(function() {
  // setup
  var cache = {};

  // setup the audio context
  var ctx = null,
    usingWebAudio = true,
    noAudio = false;
  if (typeof AudioContext !== 'undefined') {
    ctx = new AudioContext();
  } else if (typeof webkitAudioContext !== 'undefined') {
    ctx = new webkitAudioContext();
  } else if (typeof Audio !== 'undefined') {
    usingWebAudio = false;
  } else {
    usingWebAudio = false;
    noAudio = true;
  }

  // create a master gain node
  if (usingWebAudio) {
    var masterGain = (typeof ctx.createGain === 'undefined') ? ctx.createGainNode() : ctx.createGain();
    masterGain.gain.value = 1;
    masterGain.connect(ctx.destination);
  }

  // create global controller
  var HowlerGlobal = function() {
    this._volume = 1;
    this._muted = false;
    this.usingWebAudio = usingWebAudio;
    this._howls = [];
  };
  HowlerGlobal.prototype = {
    /**
     * Get/set the global volume for all sounds.
     * @param  {Float} vol Volume from 0.0 to 1.0.
     * @return {Howler/Float}     Returns self or current volume.
     */
    volume: function(vol) {
      var self = this;

      // make sure volume is a number
      vol = parseFloat(vol);

      if (vol && vol >= 0 && vol <= 1) {
        self._volume = vol;

        if (usingWebAudio) {
          masterGain.gain.value = vol;
        }

        // loop through cache and change volume of all nodes that are using HTML5 Audio
        for (var key in self._howls) {
          if (self._howls.hasOwnProperty(key) && self._howls[key]._webAudio === false) {
            // loop through the audio nodes
            for (var i=0; i<self._howls[key]._audioNode.length; i++) {
              self._howls[key]._audioNode[i].volume = self._howls[key]._volume * self._volume;
            }
          }
        }

        return self;
      }

      // return the current global volume
      return (usingWebAudio) ? masterGain.gain.value : self._volume;
    },

    /**
     * Mute all sounds.
     * @return {Howler}
     */
    mute: function() {
      this._setMuted(true);

      return this;
    },

    /**
     * Unmute all sounds.
     * @return {Howler}
     */
    unmute: function() {
      this._setMuted(false);

      return this;
    },

    /**
     * Handle muting and unmuting globally.
     * @param  {Boolean} muted Is muted or not.
     */
    _setMuted: function(muted) {
      var self = this;

      self._muted = muted;

      if (usingWebAudio) {
        masterGain.gain.value = muted ? 0 : self._volume;
      }

      for (var key in self._howls) {
        if (self._howls.hasOwnProperty(key) && self._howls[key]._webAudio === false) {
          // loop through the audio nodes
          for (var i=0; i<self._howls[key]._audioNode.length; i++) {
            self._howls[key]._audioNode[i].muted = muted;
          }
        }
      }
    }
  };

  // allow access to the global audio controls
  var Howler = new HowlerGlobal();

  // check for browser codec support
  var audioTest = null;
  if (!noAudio) {
    audioTest = new Audio();
    var codecs = {
      mp3: !!audioTest.canPlayType('audio/mpeg;').replace(/^no$/,''),
      opus: !!audioTest.canPlayType('audio/ogg; codecs="opus"').replace(/^no$/,''),
      ogg: !!audioTest.canPlayType('audio/ogg; codecs="vorbis"').replace(/^no$/,''),
      wav: !!audioTest.canPlayType('audio/wav; codecs="1"').replace(/^no$/,''),
      m4a: !!(audioTest.canPlayType('audio/x-m4a;') || audioTest.canPlayType('audio/aac;')).replace(/^no$/,''),
      webm: !!audioTest.canPlayType('audio/webm; codecs="vorbis"').replace(/^no$/,'')
    };
  }

  // setup the audio object
  var Howl = function(o) {
    var self = this;

    // setup the defaults
    self._autoplay = o.autoplay || false;
    self._buffer = o.buffer || false;
    self._duration = o.duration || 0;
    self._format = o.format || null;
    self._loop = o.loop || false;
    self._loaded = false;
    self._sprite = o.sprite || {};
    self._src = o.src || '';
    self._pos3d = o.pos3d || [0, 0, -0.5];
    self._volume = o.volume || 1;
    self._urls = o.urls || [];

    // setup event functions
    self._onload = [o.onload || function() {}];
    self._onloaderror = [o.onloaderror || function() {}];
    self._onend = [o.onend || function() {}];
    self._onpause = [o.onpause || function() {}];
    self._onplay = [o.onplay || function() {}];

    self._onendTimer = [];

    // Web Audio or HTML5 Audio?
    self._webAudio = usingWebAudio && !self._buffer;

    // check if we need to fall back to HTML5 Audio
    self._audioNode = [];
    if (self._webAudio) {
      self._setupAudioNode();
    }

    // add this to an array of Howl's to allow global control
    Howler._howls.push(self);

    // load the track
    self.load();
  };

  // setup all of the methods
  Howl.prototype = {
    /**
     * Load an audio file.
     * @return {Howl}
     */
    load: function() {
      var self = this,
        url = null;

      // if no audio is available, quit immediately
      if (noAudio) {
        self.on('loaderror');
        return;
      }

      var canPlay = {
        mp3: codecs.mp3,
        opus: codecs.opus,
        ogg: codecs.ogg,
        wav: codecs.wav,
        m4a: codecs.m4a,
        weba: codecs.webm
      };

      // loop through source URLs and pick the first one that is compatible
      for (var i=0; i<self._urls.length; i++) {
        var ext;

        if (self._format) {
          // use specified audio format if available
          ext = self._format;
        } else {
          // figure out the filetype (whether an extension or base64 data)
          ext = self._urls[i].toLowerCase().match(/.+\.([^?]+)(\?|$)/);
          ext = (ext && ext.length >= 2) ? ext[1] : self._urls[i].toLowerCase().match(/data\:audio\/([^?]+);/)[1];
        }

        if (canPlay[ext]) {
          url = self._urls[i];
          break;
        }
      }

      if (!url) {
        self.on('loaderror');
        return;
      }

      self._src = url;

      if (self._webAudio) {
        loadBuffer(self, url);
      } else {
        var newNode = new Audio();
        self._audioNode.push(newNode);

        // setup the new audio node
        newNode.src = url;
        newNode._pos = 0;
        newNode.preload = 'auto';
        newNode.volume = (Howler._muted) ? 0 : self._volume * Howler.volume();

        // add this sound to the cache
        cache[url] = self;

        // setup the event listener to start playing the sound
        // as soon as it has buffered enough
        var listener = function() {
          self._duration = newNode.duration;

          // setup a sprite if none is defined
          if (Object.getOwnPropertyNames(self._sprite).length === 0) {
            self._sprite = {_default: [0, self._duration * 1000]};
          }

          if (!self._loaded) {
            self._loaded = true;
            self.on('load');
          }

          if (self._autoplay) {
            self.play();
          }

          // clear the event listener
          newNode.removeEventListener('canplaythrough', listener, false);
        };
        newNode.addEventListener('canplaythrough', listener, false);
        newNode.load();
      }

      return self;
    },

    /**
     * Get/set the URLs to be pulled from to play in this source.
     * @param  {Array} urls  Arry of URLs to load from
     * @return {Howl}        Returns self or the current URLs
     */
    urls: function(urls) {
      var self = this;

      if (urls) {
        self.stop();
        self._urls = (typeof urls === 'string') ? [urls] : urls;
        self._loaded = false;
        self.load();

        return self;
      } else {
        return self._urls;
      }
    },

    /**
     * Play a sound from the current time (0 by default).
     * @param  {String}   sprite   (optional) Plays from the specified position in the sound sprite definition.
     * @param  {Function} callback (optional) Returns the unique playback id for this sound instance.
     * @return {Howl}
     */
    play: function(sprite, callback) {
      var self = this;

      // if no sprite was passed but a callback was, update the variables
      if (typeof sprite === 'function') {
        callback = sprite;
      }

      // use the default sprite if none is passed
      if (!sprite || typeof sprite === 'function') {
        sprite = '_default';
      }

      // if the sound hasn't been loaded, add it to the event queue
      if (!self._loaded) {
        self.on('load', function() {
          self.play(sprite, callback);
        });

        return self;
      }

      // if the sprite doesn't exist, play nothing
      if (!self._sprite[sprite]) {
        if (typeof callback === 'function') callback();
        return self;
      }

      // get the node to playback
      self._inactiveNode(function(node) {
        // persist the sprite being played
        node._sprite = sprite;

        // determine where to start playing from
        var pos = (node._pos > 0) ? node._pos : self._sprite[sprite][0] / 1000,
          duration = self._sprite[sprite][1] / 1000 - node._pos;

        // determine if this sound should be looped
        var loop = !!(self._loop || self._sprite[sprite][2]);

        // set timer to fire the 'onend' event
        var soundId = (typeof callback === 'string') ? callback : Math.round(Date.now() * Math.random()) + '',
          timerId;
        (function() {
          var data = {
            id: soundId,
            sprite: sprite,
            loop: loop
          };
          timerId = setTimeout(function() {
            // if looping, restart the track
            if (!self._webAudio && loop) {
              self.stop(data.id, data.timer).play(sprite, data.id);
            }

            // set web audio node to paused at end
            if (self._webAudio && !loop) {
              self._nodeById(data.id).paused = true;
            }

            // end the track if it is HTML audio and a sprite
            if (!self._webAudio && !loop) {
              self.stop(data.id, data.timer);
            }

            // fire ended event
            self.on('end', soundId);
          }, duration * 1000);

          // store the reference to the timer
          self._onendTimer.push(timerId);

          // remember which timer to cancel
          data.timer = self._onendTimer[self._onendTimer.length - 1];
        })();

        if (self._webAudio) {
          var loopStart = self._sprite[sprite][0] / 1000,
            loopEnd = self._sprite[sprite][1] / 1000;

          // set the play id to this node and load into context
          node.id = soundId;
          node.paused = false;
          refreshBuffer(self, [loop, loopStart, loopEnd], soundId);
          self._playStart = ctx.currentTime;
          node.gain.value = self._volume;

          if (typeof node.bufferSource.start === 'undefined') {
            node.bufferSource.noteGrainOn(0, pos, duration);
          } else {
            node.bufferSource.start(0, pos, duration);
          }
        } else {
          if (node.readyState === 4) {
            node.id = soundId;
            node.currentTime = pos;
            node.muted = Howler._muted;
            node.volume = self._volume * Howler.volume();
            setTimeout(function() { node.play(); }, 0);
          } else {
            self._clearEndTimer(timerId);

            (function(){
              var sound = self,
                playSprite = sprite,
                fn = callback,
                newNode = node;
              var listener = function() {
                sound.play(playSprite, fn);

                // clear the event listener
                newNode.removeEventListener('canplaythrough', listener, false);
              };
              newNode.addEventListener('canplaythrough', listener, false);
            })();

            return self;
          }
        }

        // fire the play event and send the soundId back in the callback
        self.on('play');
        if (typeof callback === 'function') callback(soundId);

        return self;
      });

      return self;
    },

    /**
     * Pause playback and save the current position.
     * @param {String} id (optional) The play instance ID.
     * @param {String} timerId (optional) Clear the correct timeout ID.
     * @return {Howl}
     */
    pause: function(id, timerId) {
      var self = this;

      // if the sound hasn't been loaded, add it to the event queue
      if (!self._loaded) {
        self.on('play', function() {
          self.pause(id);
        });

        return self;
      }

      // clear 'onend' timer
      self._clearEndTimer(timerId || 0);

      var activeNode = (id) ? self._nodeById(id) : self._activeNode();
      if (activeNode) {
        activeNode._pos = self.pos(null, id);

        if (self._webAudio) {
          // make sure the sound has been created
          if (!activeNode.bufferSource) {
            return self;
          }

          activeNode.paused = true;
          if (typeof activeNode.bufferSource.stop === 'undefined') {
            activeNode.bufferSource.noteOff(0);
          } else {
            activeNode.bufferSource.stop(0);
          }
        } else {
          activeNode.pause();
        }
      }

      self.on('pause');

      return self;
    },

    /**
     * Stop playback and reset to start.
     * @param  {String} id  (optional) The play instance ID.
     * @param  {String} timerId  (optional) Clear the correct timeout ID.
     * @return {Howl}
     */
    stop: function(id, timerId) {
      var self = this;

      // if the sound hasn't been loaded, add it to the event queue
      if (!self._loaded) {
        self.on('play', function() {
          self.stop(id);
        });

        return self;
      }

      // clear 'onend' timer
      self._clearEndTimer(timerId || 0);

      var activeNode = (id) ? self._nodeById(id) : self._activeNode();
      if (activeNode) {
        activeNode._pos = 0;

        if (self._webAudio) {
          // make sure the sound has been created
          if (!activeNode.bufferSource) {
            return self;
          }

          activeNode.paused = true;

          if (typeof activeNode.bufferSource.stop === 'undefined') {
            activeNode.bufferSource.noteOff(0);
          } else {
            activeNode.bufferSource.stop(0);
          }
        } else {
          activeNode.pause();
          activeNode.currentTime = 0;
        }
      }

      return self;
    },

    /**
     * Mute this sound.
     * @param  {String} id (optional) The play instance ID.
     * @return {Howl}
     */
    mute: function(id) {
      var self = this;

      // if the sound hasn't been loaded, add it to the event queue
      if (!self._loaded) {
        self.on('play', function() {
          self.mute(id);
        });

        return self;
      }

      var activeNode = (id) ? self._nodeById(id) : self._activeNode();
      if (activeNode) {
        if (self._webAudio) {
          activeNode.gain.value = 0;
        } else {
          activeNode.volume = 0;
        }
      }

      return self;
    },

    /**
     * Unmute this sound.
     * @param  {String} id (optional) The play instance ID.
     * @return {Howl}
     */
    unmute: function(id) {
      var self = this;

      // if the sound hasn't been loaded, add it to the event queue
      if (!self._loaded) {
        self.on('play', function() {
          self.unmute(id);
        });

        return self;
      }

      var activeNode = (id) ? self._nodeById(id) : self._activeNode();
      if (activeNode) {
        if (self._webAudio) {
          activeNode.gain.value = self._volume;
        } else {
          activeNode.volume = self._volume;
        }
      }

      return self;
    },

    /**
     * Get/set volume of this sound.
     * @param  {Float}  vol Volume from 0.0 to 1.0.
     * @param  {String} id  (optional) The play instance ID.
     * @return {Howl/Float}     Returns self or current volume.
     */
    volume: function(vol, id) {
      var self = this;

      // make sure volume is a number
      vol = parseFloat(vol);

      if (vol >= 0 && vol <= 1) {
        self._volume = vol;

        // if the sound hasn't been loaded, add it to the event queue
        if (!self._loaded) {
          self.on('play', function() {
            self.volume(vol, id);
          });

          return self;
        }

        var activeNode = (id) ? self._nodeById(id) : self._activeNode();
        if (activeNode) {
          if (self._webAudio) {
            activeNode.gain.value = vol;
          } else {
            activeNode.volume = vol * Howler.volume();
          }
        }

        return self;
      } else {
        return self._volume;
      }
    },

    /**
     * Get/set whether to loop the sound.
     * @param  {Boolean} loop To loop or not to loop, that is the question.
     * @return {Howl/Boolean}      Returns self or current looping value.
     */
    loop: function(loop) {
      var self = this;

      if (typeof loop === 'boolean') {
        self._loop = loop;

        return self;
      } else {
        return self._loop;
      }
    },

    /**
     * Get/set sound sprite definition.
     * @param  {Object} sprite Example: {spriteName: [offset, duration, loop]}
     *                @param {Integer} offset   Where to begin playback in milliseconds
     *                @param {Integer} duration How long to play in milliseconds
     *                @param {Boolean} loop     (optional) Set true to loop this sprite
     * @return {Howl}        Returns current sprite sheet or self.
     */
    sprite: function(sprite) {
      var self = this;

      if (typeof sprite === 'object') {
        self._sprite = sprite;

        return self;
      } else {
        return self._sprite;
      }
    },

    /**
     * Get/set the position of playback.
     * @param  {Float}  pos The position to move current playback to.
     * @param  {String} id  (optional) The play instance ID.
     * @return {Howl/Float}      Returns self or current playback position.
     */
    pos: function(pos, id) {
      var self = this;

      // if the sound hasn't been loaded, add it to the event queue
      if (!self._loaded) {
        self.on('load', function() {
          self.pos(pos);
        });

        return typeof pos === 'number' ? self : self._pos || 0;
      }

      // make sure we are dealing with a number for pos
      pos = parseFloat(pos);

      var activeNode = (id) ? self._nodeById(id) : self._activeNode();
      if (activeNode) {
        if (self._webAudio) {
          if (pos >= 0) {
            activeNode._pos = pos;
            self.pause(id).play(activeNode._sprite, id);

            return self;
          } else {
            return activeNode._pos + (ctx.currentTime - self._playStart);
          }
        } else {
          if (pos >= 0) {
            activeNode.currentTime = pos;

            return self;
          } else {
            return activeNode.currentTime;
          }
        }
      } else if (pos >= 0) {
        return self;
      } else {
        // find the first inactive node to return the pos for
        for (var i=0; i<self._audioNode.length; i++) {
          if (self._audioNode[i].paused && self._audioNode[i].readyState === 4) {
            return (self._webAudio) ? self._audioNode[i]._pos : self._audioNode[i].currentTime;
          }
        }
      }
    },

    /**
     * Get/set the 3D position of the audio source.
     * The most common usage is to set the 'x' position
     * to affect the left/right ear panning. Setting any value higher than
     * 1.0 will begin to decrease the volume of the sound as it moves further away.
     * NOTE: This only works with Web Audio API, HTML5 Audio playback
     * will not be affected.
     * @param  {Float}  x  The x-position of the playback from -1000.0 to 1000.0
     * @param  {Float}  y  The y-position of the playback from -1000.0 to 1000.0
     * @param  {Float}  z  The z-position of the playback from -1000.0 to 1000.0
     * @param  {String} id (optional) The play instance ID.
     * @return {Howl/Array}   Returns self or the current 3D position: [x, y, z]
     */
    pos3d: function(x, y, z, id) {
      var self = this;

      // set a default for the optional 'y' & 'z'
      y = (typeof y === 'undefined' || !y) ? 0 : y;
      z = (typeof z === 'undefined' || !z) ? -0.5 : z;

      // if the sound hasn't been loaded, add it to the event queue
      if (!self._loaded) {
        self.on('play', function() {
          self.pos3d(x, y, z, id);
        });

        return self;
      }

      if (x >= 0 || x < 0) {
        if (self._webAudio) {
          var activeNode = (id) ? self._nodeById(id) : self._activeNode();
          if (activeNode) {
            self._pos3d = [x, y, z];
            activeNode.panner.setPosition(x, y, z);
          }
        }
      } else {
        return self._pos3d;
      }

      return self;
    },

    /**
     * Fade a currently playing sound between two volumes.
     * @param  {Number}   from     The volume to fade from (0.0 to 1.0).
     * @param  {Number}   to       The volume to fade to (0.0 to 1.0).
     * @param  {Number}   len      Time in milliseconds to fade.
     * @param  {Function} callback (optional) Fired when the fade is complete.
     * @param  {String}   id       (optional) The play instance ID.
     * @return {Howl}
     */
    fade: function(from, to, len, callback, id) {
      var self = this,
        diff = Math.abs(from - to),
        dir = from > to ? 'down' : 'up',
        steps = diff / 0.01,
        stepTime = len / steps;

      // if the sound hasn't been loaded, add it to the event queue
      if (!self._loaded) {
        self.on('load', function() {
          self.fade(from, to, len, callback, id);
        });

        return self;
      }

      // set the volume to the start position
      self.volume(from, id);

      for (var i=1; i<=steps; i++) {
        (function() {
          var change = self._volume + (dir === 'up' ? 0.01 : -0.01) * i,
            vol = Math.round(1000 * change) / 1000,
            toVol = to;

          setTimeout(function() {
            self.volume(vol, id);

            if (vol === toVol) {
              if (callback) callback();
            }
          }, stepTime * i);
        })();
      }
    },

    /**
     * [DEPRECATED] Fade in the current sound.
     * @param  {Float}    to      Volume to fade to (0.0 to 1.0).
     * @param  {Number}   len     Time in milliseconds to fade.
     * @param  {Function} callback
     * @return {Howl}
     */
    fadeIn: function(to, len, callback) {
      return this.volume(0).play().fade(0, to, len, callback);
    },

    /**
     * [DEPRECATED] Fade out the current sound and pause when finished.
     * @param  {Float}    to       Volume to fade to (0.0 to 1.0).
     * @param  {Number}   len      Time in milliseconds to fade.
     * @param  {Function} callback
     * @param  {String}   id       (optional) The play instance ID.
     * @return {Howl}
     */
    fadeOut: function(to, len, callback, id) {
      var self = this;

      return self.fade(self._volume, to, len, function() {
        if (callback) callback();
        self.pause(id);

        // fire ended event
        self.on('end');
      }, id);
    },

    /**
     * Get an audio node by ID.
     * @return {Howl} Audio node.
     */
    _nodeById: function(id) {
      var self = this,
        node = self._audioNode[0];

      // find the node with this ID
      for (var i=0; i<self._audioNode.length; i++) {
        if (self._audioNode[i].id === id) {
          node = self._audioNode[i];
          break;
        }
      }

      return node;
    },

    /**
     * Get the first active audio node.
     * @return {Howl} Audio node.
     */
    _activeNode: function() {
      var self = this,
        node = null;

      // find the first playing node
      for (var i=0; i<self._audioNode.length; i++) {
        if (!self._audioNode[i].paused) {
          node = self._audioNode[i];
          break;
        }
      }

      // remove excess inactive nodes
      self._drainPool();

      return node;
    },

    /**
     * Get the first inactive audio node.
     * If there is none, create a new one and add it to the pool.
     * @param  {Function} callback Function to call when the audio node is ready.
     */
    _inactiveNode: function(callback) {
      var self = this,
        node = null;

      // find first inactive node to recycle
      for (var i=0; i<self._audioNode.length; i++) {
        if (self._audioNode[i].paused && self._audioNode[i].readyState === 4) {
          callback(self._audioNode[i]);
          node = true;
          break;
        }
      }

      // remove excess inactive nodes
      self._drainPool();

      if (node) {
        return;
      }

      // create new node if there are no inactives
      var newNode;
      if (self._webAudio) {
        newNode = self._setupAudioNode();
        callback(newNode);
      } else {
        self.load();
        newNode = self._audioNode[self._audioNode.length - 1];
        newNode.addEventListener('loadedmetadata', function() {
          callback(newNode);
        });
      }
    },

    /**
     * If there are more than 5 inactive audio nodes in the pool, clear out the rest.
     */
    _drainPool: function() {
      var self = this,
        inactive = 0,
        i;

      // count the number of inactive nodes
      for (i=0; i<self._audioNode.length; i++) {
        if (self._audioNode[i].paused) {
          inactive++;
        }
      }

      // remove excess inactive nodes
      for (i=self._audioNode.length-1; i>=0; i--) {
        if (inactive <= 5) {
          break;
        }

        if (self._audioNode[i].paused) {
          // disconnect the audio source if using Web Audio
          if (self._webAudio) {
            self._audioNode[i].disconnect(0);
          }

          inactive--;
          self._audioNode.splice(i, 1);
        }
      }
    },

    /**
     * Clear 'onend' timeout before it ends.
     * @param  {Number} timerId The ID of the sound to be cancelled.
     */
    _clearEndTimer: function(timerId) {
      var self = this,
        timer = self._onendTimer.indexOf(timerId);

      // make sure the timer gets cleared
      timer = timer >= 0 ? timer : 0;

      if (self._onendTimer[timer]) {
        clearTimeout(self._onendTimer[timer]);
        self._onendTimer.splice(timer, 1);
      }
    },

    /**
     * Setup the gain node and panner for a Web Audio instance.
     * @return {Object} The new audio node.
     */
    _setupAudioNode: function() {
      var self = this,
        node = self._audioNode,
        index = self._audioNode.length;

      // create gain node
      node[index] = (typeof ctx.createGain === 'undefined') ? ctx.createGainNode() : ctx.createGain();
      node[index].gain.value = self._volume;
      node[index].paused = true;
      node[index]._pos = 0;
      node[index].readyState = 4;
      node[index].connect(masterGain);

      // create the panner
      node[index].panner = ctx.createPanner();
      node[index].panner.setPosition(self._pos3d[0], self._pos3d[1], self._pos3d[2]);
      node[index].panner.connect(node[index]);

      return node[index];
    },

    /**
     * Call/set custom events.
     * @param  {String}   event Event type.
     * @param  {Function} fn    Function to call.
     * @return {Howl}
     */
    on: function(event, fn) {
      var self = this,
        events = self['_on' + event];

      if (typeof fn === "function") {
        events.push(fn);
      } else {
        for (var i=0; i<events.length; i++) {
          if (fn) {
            events[i].call(self, fn);
          } else {
            events[i].call(self);
          }
        }
      }

      return self;
    },

    /**
     * Remove a custom event.
     * @param  {String}   event Event type.
     * @param  {Function} fn    Listener to remove.
     * @return {Howl}
     */
    off: function(event, fn) {
      var self = this,
        events = self['_on' + event],
        fnString = fn.toString();

      // loop through functions in the event for comparison
      for (var i=0; i<events.length; i++) {
        if (fnString === events[i].toString()) {
          events.splice(i, 1);
          break;
        }
      }

      return self;
    },

    /**
     * Unload and destroy the current Howl object.
     * This will immediately stop all play instances attached to this sound.
     */
    unload: function() {
      var self = this;

      // stop playing any active nodes
      var nodes = self._audioNode;
      for (var i=0; i<self._audioNode.length; i++) {
        self.stop(nodes[i].id);

        if (!self._webAudio) {
           // remove the source if using HTML5 Audio
          nodes[i].src = '';
        } else {
          // disconnect the output from the master gain
          nodes[i].disconnect(0);
        }
      }

      // remove the reference in the global Howler object
      var index = Howler._howls.indexOf(self);
      if (index) {
        Howler._howls.splice(index, 1);
      }

      // delete this sound from the cache
      delete cache[self._src];
      self = null;
    }

  };

  // only define these functions when using WebAudio
  if (usingWebAudio) {

    /**
     * Buffer a sound from URL (or from cache) and decode to audio source (Web Audio API).
     * @param  {Object} obj The Howl object for the sound to load.
     * @param  {String} url The path to the sound file.
     */
    var loadBuffer = function(obj, url) {
      // check if the buffer has already been cached
      if (url in cache) {
        // set the duration from the cache
        obj._duration = cache[url].duration;

        // load the sound into this object
        loadSound(obj);
      } else {
        // load the buffer from the URL
        var xhr = new XMLHttpRequest();
        xhr.open('GET', url, true);
        xhr.responseType = 'arraybuffer';
        xhr.onload = function() {
          // decode the buffer into an audio source
          ctx.decodeAudioData(xhr.response, function(buffer) {
            if (buffer) {
              cache[url] = buffer;
              loadSound(obj, buffer);
            }
          });
        };
        xhr.onerror = function() {
          // if there is an error, switch the sound to HTML Audio
          if (obj._webAudio) {
            obj._buffer = true;
            obj._webAudio = false;
            obj._audioNode = [];
            delete obj._gainNode;
            obj.load();
          }
        };
        try {
          xhr.send();
        } catch (e) {
          xhr.onerror();
        }
      }
    };

    /**
     * Finishes loading the Web Audio API sound and fires the loaded event
     * @param  {Object}  obj    The Howl object for the sound to load.
     * @param  {Objecct} buffer The decoded buffer sound source.
     */
    var loadSound = function(obj, buffer) {
      // set the duration
      obj._duration = (buffer) ? buffer.duration : obj._duration;

      // setup a sprite if none is defined
      if (Object.getOwnPropertyNames(obj._sprite).length === 0) {
        obj._sprite = {_default: [0, obj._duration * 1000]};
      }

      // fire the loaded event
      if (!obj._loaded) {
        obj._loaded = true;
        obj.on('load');
      }

      if (obj._autoplay) {
        obj.play();
      }
    };

    /**
     * Load the sound back into the buffer source.
     * @param  {Object} obj   The sound to load.
     * @param  {Array}  loop  Loop boolean, pos, and duration.
     * @param  {String} id    (optional) The play instance ID.
     */
    var refreshBuffer = function(obj, loop, id) {
      // determine which node to connect to
      var node = obj._nodeById(id);

      // setup the buffer source for playback
      node.bufferSource = ctx.createBufferSource();
      node.bufferSource.buffer = cache[obj._src];
      node.bufferSource.connect(node.panner);
      node.bufferSource.loop = loop[0];
      if (loop[0]) {
        node.bufferSource.loopStart = loop[1];
        node.bufferSource.loopEnd = loop[1] + loop[2];
      }
    };

  }

  /**
   * Add support for AMD (Async Module Definition) libraries such as require.js.
   */
  if (typeof define === 'function' && define.amd) {
    define('Howler', function() {
      return {
        Howler: Howler,
        Howl: Howl
      };
    });
  } else {
    window.Howler = Howler;
    window.Howl = Howl;
  }
})();