howler.core.js

/*!
 *  howler.js v2.0.1
 *  howlerjs.com
 *
 *  (c) 2013-2016, James Simpson of GoldFire Studios
 *  goldfirestudios.com
 *
 *  MIT License
 */

(function() {

  'use strict';

  /** Global Methods **/
  /***************************************************************************/

  /**
   * Create the global controller. All contained methods and properties apply
   * to all sounds that are currently playing or will be in the future.
   */
  var HowlerGlobal = function() {
    this.init();
  };
  HowlerGlobal.prototype = {
    /**
     * Initialize the global Howler object.
     * @return {Howler}
     */
    init: function() {
      var self = this || Howler;

      // Internal properties.
      self._codecs = {};
      self._howls = [];
      self._muted = false;
      self._volume = 1;
      self._canPlayEvent = 'canplaythrough';
      self._navigator = (typeof window !== 'undefined' && window.navigator) ? window.navigator : null;

      // Public properties.
      self.masterGain = null;
      self.noAudio = false;
      self.usingWebAudio = true;
      self.autoSuspend = true;
      self.ctx = null;

      // Set to false to disable the auto iOS enabler.
      self.mobileAutoEnable = true;

      // Setup the various state values for global tracking.
      self._setup();

      return self;
    },

    /**
     * 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 || Howler;
      vol = parseFloat(vol);

      // If we don't have an AudioContext created yet, run the setup.
      if (!self.ctx) {
        setupAudioContext();
      }

      if (typeof vol !== 'undefined' && vol >= 0 && vol <= 1) {
        self._volume = vol;

        // Don't update any of the nodes if we are muted.
        if (self._muted) {
          return self;
        }

        // When using Web Audio, we just need to adjust the master gain.
        if (self.usingWebAudio) {
          self.masterGain.gain.value = vol;
        }

        // Loop through and change volume for all HTML5 audio nodes.
        for (var i=0; i<self._howls.length; i++) {
          if (!self._howls[i]._webAudio) {
            // Get all of the sounds in this Howl group.
            var ids = self._howls[i]._getSoundIds();

            // Loop through all sounds and change the volumes.
            for (var j=0; j<ids.length; j++) {
              var sound = self._howls[i]._soundById(ids[j]);

              if (sound && sound._node) {
                sound._node.volume = sound._volume * vol;
              }
            }
          }
        }

        return self;
      }

      return self._volume;
    },

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

      // If we don't have an AudioContext created yet, run the setup.
      if (!self.ctx) {
        setupAudioContext();
      }

      self._muted = muted;

      // With Web Audio, we just need to mute the master gain.
      if (self.usingWebAudio) {
        self.masterGain.gain.value = muted ? 0 : self._volume;
      }

      // Loop through and mute all HTML5 Audio nodes.
      for (var i=0; i<self._howls.length; i++) {
        if (!self._howls[i]._webAudio) {
          // Get all of the sounds in this Howl group.
          var ids = self._howls[i]._getSoundIds();

          // Loop through all sounds and mark the audio node as muted.
          for (var j=0; j<ids.length; j++) {
            var sound = self._howls[i]._soundById(ids[j]);

            if (sound && sound._node) {
              sound._node.muted = (muted) ? true : sound._muted;
            }
          }
        }
      }

      return self;
    },

    /**
     * Unload and destroy all currently loaded Howl objects.
     * @return {Howler}
     */
    unload: function() {
      var self = this || Howler;

      for (var i=self._howls.length-1; i>=0; i--) {
        self._howls[i].unload();
      }

      // Create a new AudioContext to make sure it is fully reset.
      if (self.usingWebAudio && self.ctx && typeof self.ctx.close !== 'undefined') {
        self.ctx.close();
        self.ctx = null;
        setupAudioContext();
      }

      return self;
    },

    /**
     * Check for codec support of specific extension.
     * @param  {String} ext Audio file extention.
     * @return {Boolean}
     */
    codecs: function(ext) {
      return (this || Howler)._codecs[ext.replace(/^x-/, '')];
    },

    /**
     * Setup various state values for global tracking.
     * @return {Howler}
     */
    _setup: function() {
      var self = this || Howler;

      // Keeps track of the suspend/resume state of the AudioContext.
      self.state = self.ctx ? self.ctx.state || 'running' : 'running';

      // Automatically begin the 30-second suspend process
      self._autoSuspend();

      // Check if audio is available.
      if (!self.usingWebAudio) {
        // No audio is available on this system if noAudio is set to true.
        if (typeof Audio !== 'undefined') {
          try {
            var test = new Audio();

            // Check if the canplaythrough event is available.
            if (typeof test.oncanplaythrough === 'undefined') {
              self._canPlayEvent = 'canplay';
            }
          } catch(e) {
            self.noAudio = true;
          }
        } else {
          self.noAudio = true;
        }
      }

      // Test to make sure audio isn't disabled in Internet Explorer.
      try {
        var test = new Audio();
        if (test.muted) {
          self.noAudio = true;
        }
      } catch (e) {}

      // Check for supported codecs.
      if (!self.noAudio) {
        self._setupCodecs();
      }

      return self;
    },

    /**
     * Check for browser support for various codecs and cache the results.
     * @return {Howler}
     */
    _setupCodecs: function() {
      var self = this || Howler;
      var audioTest = null;

      // Must wrap in a try/catch because IE11 in server mode throws an error.
      try {
        audioTest = (typeof Audio !== 'undefined') ? new Audio() : null;
      } catch (err) {
        return self;
      }

      if (!audioTest || typeof audioTest.canPlayType !== 'function') {
        return self;
      }

      var mpegTest = audioTest.canPlayType('audio/mpeg;').replace(/^no$/, '');

      // Opera version <33 has mixed MP3 support, so we need to check for and block it.
      var checkOpera = self._navigator && self._navigator.userAgent.match(/OPR\/([0-6].)/g);
      var isOldOpera = (checkOpera && parseInt(checkOpera[0].split('/')[1], 10) < 33);

      self._codecs = {
        mp3: !!(!isOldOpera && (mpegTest || audioTest.canPlayType('audio/mp3;').replace(/^no$/, ''))),
        mpeg: !!mpegTest,
        opus: !!audioTest.canPlayType('audio/ogg; codecs="opus"').replace(/^no$/, ''),
        ogg: !!audioTest.canPlayType('audio/ogg; codecs="vorbis"').replace(/^no$/, ''),
        oga: !!audioTest.canPlayType('audio/ogg; codecs="vorbis"').replace(/^no$/, ''),
        wav: !!audioTest.canPlayType('audio/wav; codecs="1"').replace(/^no$/, ''),
        aac: !!audioTest.canPlayType('audio/aac;').replace(/^no$/, ''),
        caf: !!audioTest.canPlayType('audio/x-caf;').replace(/^no$/, ''),
        m4a: !!(audioTest.canPlayType('audio/x-m4a;') || audioTest.canPlayType('audio/m4a;') || audioTest.canPlayType('audio/aac;')).replace(/^no$/, ''),
        mp4: !!(audioTest.canPlayType('audio/x-mp4;') || audioTest.canPlayType('audio/mp4;') || audioTest.canPlayType('audio/aac;')).replace(/^no$/, ''),
        weba: !!audioTest.canPlayType('audio/webm; codecs="vorbis"').replace(/^no$/, ''),
        webm: !!audioTest.canPlayType('audio/webm; codecs="vorbis"').replace(/^no$/, ''),
        dolby: !!audioTest.canPlayType('audio/mp4; codecs="ec-3"').replace(/^no$/, ''),
        flac: !!(audioTest.canPlayType('audio/x-flac;') || audioTest.canPlayType('audio/flac;')).replace(/^no$/, '')
      };

      return self;
    },

    /**
     * Mobile browsers will only allow audio to be played after a user interaction.
     * Attempt to automatically unlock audio on the first user interaction.
     * Concept from: http://paulbakaus.com/tutorials/html5/web-audio-on-ios/
     * @return {Howler}
     */
    _enableMobileAudio: function() {
      var self = this || Howler;

      // Only run this on mobile devices if audio isn't already eanbled.
      var isMobile = /iPhone|iPad|iPod|Android|BlackBerry|BB10|Silk|Mobi/i.test(self._navigator && self._navigator.userAgent);
      var isTouch = !!(('ontouchend' in window) || (self._navigator && self._navigator.maxTouchPoints > 0) || (self._navigator && self._navigator.msMaxTouchPoints > 0));
      if (self._mobileEnabled || !self.ctx || (!isMobile && !isTouch)) {
        return;
      }

      self._mobileEnabled = false;

      // Some mobile devices/platforms have distortion issues when opening/closing tabs and/or web views.
      // Bugs in the browser (especially Mobile Safari) can cause the sampleRate to change from 44100 to 48000.
      // By calling Howler.unload(), we create a new AudioContext with the correct sampleRate.
      if (!self._mobileUnloaded && self.ctx.sampleRate !== 44100) {
        self._mobileUnloaded = true;
        self.unload();
      }

      // Scratch buffer for enabling iOS to dispose of web audio buffers correctly, as per:
      // http://stackoverflow.com/questions/24119684
      self._scratchBuffer = self.ctx.createBuffer(1, 1, 22050);

      // Call this method on touch start to create and play a buffer,
      // then check if the audio actually played to determine if
      // audio has now been unlocked on iOS, Android, etc.
      var unlock = function() {
        // Create an empty buffer.
        var source = self.ctx.createBufferSource();
        source.buffer = self._scratchBuffer;
        source.connect(self.ctx.destination);

        // Play the empty buffer.
        if (typeof source.start === 'undefined') {
          source.noteOn(0);
        } else {
          source.start(0);
        }

        // Setup a timeout to check that we are unlocked on the next event loop.
        source.onended = function() {
          source.disconnect(0);

          // Update the unlocked state and prevent this check from happening again.
          self._mobileEnabled = true;
          self.mobileAutoEnable = false;

          // Remove the touch start listener.
          document.removeEventListener('touchend', unlock, true);
        };
      };

      // Setup a touch start listener to attempt an unlock in.
      document.addEventListener('touchend', unlock, true);

      return self;
    },

    /**
     * Automatically suspend the Web Audio AudioContext after no sound has played for 30 seconds.
     * This saves processing/energy and fixes various browser-specific bugs with audio getting stuck.
     * @return {Howler}
     */
    _autoSuspend: function() {
      var self = this;

      if (!self.autoSuspend || !self.ctx || typeof self.ctx.suspend === 'undefined' || !Howler.usingWebAudio) {
        return;
      }

      // Check if any sounds are playing.
      for (var i=0; i<self._howls.length; i++) {
        if (self._howls[i]._webAudio) {
          for (var j=0; j<self._howls[i]._sounds.length; j++) {
            if (!self._howls[i]._sounds[j]._paused) {
              return self;
            }
          }
        }
      }

      if (self._suspendTimer) {
        clearTimeout(self._suspendTimer);
      }

      // If no sound has played after 30 seconds, suspend the context.
      self._suspendTimer = setTimeout(function() {
        if (!self.autoSuspend) {
          return;
        }

        self._suspendTimer = null;
        self.state = 'suspending';
        self.ctx.suspend().then(function() {
          self.state = 'suspended';

          if (self._resumeAfterSuspend) {
            delete self._resumeAfterSuspend;
            self._autoResume();
          }
        });
      }, 30000);

      return self;
    },

    /**
     * Automatically resume the Web Audio AudioContext when a new sound is played.
     * @return {Howler}
     */
    _autoResume: function() {
      var self = this;

      if (!self.ctx || typeof self.ctx.resume === 'undefined' || !Howler.usingWebAudio) {
        return;
      }

      if (self.state === 'running' && self._suspendTimer) {
        clearTimeout(self._suspendTimer);
        self._suspendTimer = null;
      } else if (self.state === 'suspended') {
        self.state = 'resuming';
        self.ctx.resume().then(function() {
          self.state = 'running';

          // Emit to all Howls that the audio has resumed.
          for (var i=0; i<self._howls.length; i++) {
            self._howls[i]._emit('resume');
          }
        });

        if (self._suspendTimer) {
          clearTimeout(self._suspendTimer);
          self._suspendTimer = null;
        }
      } else if (self.state === 'suspending') {
        self._resumeAfterSuspend = true;
      }

      return self;
    }
  };

  // Setup the global audio controller.
  var Howler = new HowlerGlobal();

  /** Group Methods **/
  /***************************************************************************/

  /**
   * Create an audio group controller.
   * @param {Object} o Passed in properties for this group.
   */
  var Howl = function(o) {
    var self = this;

    // Throw an error if no source is provided.
    if (!o.src || o.src.length === 0) {
      console.error('An array of source files must be passed with any new Howl.');
      return;
    }

    self.init(o);
  };
  Howl.prototype = {
    /**
     * Initialize a new Howl group object.
     * @param  {Object} o Passed in properties for this group.
     * @return {Howl}
     */
    init: function(o) {
      var self = this;

      // If we don't have an AudioContext created yet, run the setup.
      if (!Howler.ctx) {
        setupAudioContext();
      }

      // Setup user-defined default properties.
      self._autoplay = o.autoplay || false;
      self._format = (typeof o.format !== 'string') ? o.format : [o.format];
      self._html5 = o.html5 || false;
      self._muted = o.mute || false;
      self._loop = o.loop || false;
      self._pool = o.pool || 5;
      self._preload = (typeof o.preload === 'boolean') ? o.preload : true;
      self._rate = o.rate || 1;
      self._sprite = o.sprite || {};
      self._src = (typeof o.src !== 'string') ? o.src : [o.src];
      self._volume = o.volume !== undefined ? o.volume : 1;

      // Setup all other default properties.
      self._duration = 0;
      self._state = 'unloaded';
      self._sounds = [];
      self._endTimers = {};
      self._queue = [];

      // Setup event listeners.
      self._onend = o.onend ? [{fn: o.onend}] : [];
      self._onfade = o.onfade ? [{fn: o.onfade}] : [];
      self._onload = o.onload ? [{fn: o.onload}] : [];
      self._onloaderror = o.onloaderror ? [{fn: o.onloaderror}] : [];
      self._onpause = o.onpause ? [{fn: o.onpause}] : [];
      self._onplay = o.onplay ? [{fn: o.onplay}] : [];
      self._onstop = o.onstop ? [{fn: o.onstop}] : [];
      self._onmute = o.onmute ? [{fn: o.onmute}] : [];
      self._onvolume = o.onvolume ? [{fn: o.onvolume}] : [];
      self._onrate = o.onrate ? [{fn: o.onrate}] : [];
      self._onseek = o.onseek ? [{fn: o.onseek}] : [];
      self._onresume = [];

      // Web Audio or HTML5 Audio?
      self._webAudio = Howler.usingWebAudio && !self._html5;

      // Automatically try to enable audio on iOS.
      if (typeof Howler.ctx !== 'undefined' && Howler.ctx && Howler.mobileAutoEnable) {
        Howler._enableMobileAudio();
      }

      // Keep track of this Howl group in the global controller.
      Howler._howls.push(self);

      // Load the source file unless otherwise specified.
      if (self._preload) {
        self.load();
      }

      return self;
    },

    /**
     * Load the audio file.
     * @return {Howler}
     */
    load: function() {
      var self = this;
      var url = null;

      // If no audio is available, quit immediately.
      if (Howler.noAudio) {
        self._emit('loaderror', null, 'No audio support.');
        return;
      }

      // Make sure our source is in an array.
      if (typeof self._src === 'string') {
        self._src = [self._src];
      }

      // Loop through the sources and pick the first one that is compatible.
      for (var i=0; i<self._src.length; i++) {
        var ext, str;

        if (self._format && self._format[i]) {
          // If an extension was specified, use that instead.
          ext = self._format[i];
        } else {
          // Make sure the source is a string.
          str = self._src[i];
          if (typeof str !== 'string') {
            self._emit('loaderror', null, 'Non-string found in selected audio sources - ignoring.');
            continue;
          }

          // Extract the file extension from the URL or base64 data URI.
          ext = /^data:audio\/([^;,]+);/i.exec(str);
          if (!ext) {
            ext = /\.([^.]+)$/.exec(str.split('?', 1)[0]);
          }

          if (ext) {
            ext = ext[1].toLowerCase();
          }
        }

        // Check if this extension is available.
        if (Howler.codecs(ext)) {
          url = self._src[i];
          break;
        }
      }

      if (!url) {
        self._emit('loaderror', null, 'No codec support for selected audio sources.');
        return;
      }

      self._src = url;
      self._state = 'loading';

      // If the hosting page is HTTPS and the source isn't,
      // drop down to HTML5 Audio to avoid Mixed Content errors.
      if (window.location.protocol === 'https:' && url.slice(0, 5) === 'http:') {
        self._html5 = true;
        self._webAudio = false;
      }

      // Create a new sound object and add it to the pool.
      new Sound(self);

      // Load and decode the audio data for playback.
      if (self._webAudio) {
        loadBuffer(self);
      }

      return self;
    },

    /**
     * Play a sound or resume previous playback.
     * @param  {String/Number} sprite   Sprite name for sprite playback or sound id to continue previous.
     * @param  {Boolean} internal Internal Use: true prevents event firing.
     * @return {Number}          Sound ID.
     */
    play: function(sprite, internal) {
      var self = this;
      var id = null;

      // Determine if a sprite, sound id or nothing was passed
      if (typeof sprite === 'number') {
        id = sprite;
        sprite = null;
      } else if (typeof sprite === 'string' && self._state === 'loaded' && !self._sprite[sprite]) {
        // If the passed sprite doesn't exist, do nothing.
        return null;
      } else if (typeof sprite === 'undefined') {
        // Use the default sound sprite (plays the full audio length).
        sprite = '__default';

        // Check if there is a single paused sound that isn't ended.
        // If there is, play that sound. If not, continue as usual.
        var num = 0;
        for (var i=0; i<self._sounds.length; i++) {
          if (self._sounds[i]._paused && !self._sounds[i]._ended) {
            num++;
            id = self._sounds[i]._id;
          }
        }

        if (num === 1) {
          sprite = null;
        } else {
          id = null;
        }
      }

      // Get the selected node, or get one from the pool.
      var sound = id ? self._soundById(id) : self._inactiveSound();

      // If the sound doesn't exist, do nothing.
      if (!sound) {
        return null;
      }

      // Select the sprite definition.
      if (id && !sprite) {
        sprite = sound._sprite || '__default';
      }

      // If we have no sprite and the sound hasn't loaded, we must wait
      // for the sound to load to get our audio's duration.
      if (self._state !== 'loaded' && !self._sprite[sprite]) {
        self._queue.push({
          event: 'play',
          action: function() {
            self.play(self._soundById(sound._id) ? sound._id : undefined);
          }
        });

        return sound._id;
      }

      // Don't play the sound if an id was passed and it is already playing.
      if (id && !sound._paused) {
        // Trigger the play event, in order to keep iterating through queue.
        if (!internal) {
          setTimeout(function() {
            self._emit('play', sound._id);
          }, 0);
        }

        return sound._id;
      }

      // Make sure the AudioContext isn't suspended, and resume it if it is.
      if (self._webAudio) {
        Howler._autoResume();
      }

      // Determine how long to play for and where to start playing.
      var seek = sound._seek > 0 ? sound._seek : self._sprite[sprite][0] / 1000;
      var duration = ((self._sprite[sprite][0] + self._sprite[sprite][1]) / 1000) - seek;
      var timeout = (duration * 1000) / Math.abs(sound._rate);

      // Update the parameters of the sound
      sound._paused = false;
      sound._ended = false;
      sound._sprite = sprite;
      sound._seek = seek;
      sound._start = self._sprite[sprite][0] / 1000;
      sound._stop = (self._sprite[sprite][0] + self._sprite[sprite][1]) / 1000;
      sound._loop = !!(sound._loop || self._sprite[sprite][2]);

      // Begin the actual playback.
      var node = sound._node;
      if (self._webAudio) {
        // Fire this when the sound is ready to play to begin Web Audio playback.
        var playWebAudio = function() {
          self._refreshBuffer(sound);

          // Setup the playback params.
          var vol = (sound._muted || self._muted) ? 0 : sound._volume;
          node.gain.setValueAtTime(vol, Howler.ctx.currentTime);
          sound._playStart = Howler.ctx.currentTime;

          // Play the sound using the supported method.
          if (typeof node.bufferSource.start === 'undefined') {
            sound._loop ? node.bufferSource.noteGrainOn(0, seek, 86400) : node.bufferSource.noteGrainOn(0, seek, duration);
          } else {
            sound._loop ? node.bufferSource.start(0, seek, 86400) : node.bufferSource.start(0, seek, duration);
          }

          // Start a new timer if none is present.
          if (timeout !== Infinity) {
            self._endTimers[sound._id] = setTimeout(self._ended.bind(self, sound), timeout);
          }

          if (!internal) {
            setTimeout(function() {
              self._emit('play', sound._id);
            }, 0);
          }
        };

        var isRunning = (Howler.state === 'running');
        if (self._state === 'loaded' && isRunning) {
          playWebAudio();
        } else {
          // Wait for the audio to load and then begin playback.
          self.once(isRunning ? 'load' : 'resume', playWebAudio, isRunning ? sound._id : null);

          // Cancel the end timer.
          self._clearTimer(sound._id);
        }
      } else {
        // Fire this when the sound is ready to play to begin HTML5 Audio playback.
        var playHtml5 = function() {
          node.currentTime = seek;
          node.muted = sound._muted || self._muted || Howler._muted || node.muted;
          node.volume = sound._volume * Howler.volume();
          node.playbackRate = sound._rate;

          setTimeout(function() {
            node.play();

            // Setup the new end timer.
            if (timeout !== Infinity) {
              self._endTimers[sound._id] = setTimeout(self._ended.bind(self, sound), timeout);
            }

            if (!internal) {
              self._emit('play', sound._id);
            }
          }, 0);
        };

        // Play immediately if ready, or wait for the 'canplaythrough'e vent.
        var loadedNoReadyState = (self._state === 'loaded' && (window && window.ejecta || !node.readyState && Howler._navigator.isCocoonJS));
        if (node.readyState === 4 || loadedNoReadyState) {
          playHtml5();
        } else {
          var listener = function() {
            // Begin playback.
            playHtml5();

            // Clear this listener.
            node.removeEventListener(Howler._canPlayEvent, listener, false);
          };
          node.addEventListener(Howler._canPlayEvent, listener, false);

          // Cancel the end timer.
          self._clearTimer(sound._id);
        }
      }

      return sound._id;
    },

    /**
     * Pause playback and save current position.
     * @param  {Number} id The sound ID (empty to pause all in group).
     * @return {Howl}
     */
    pause: function(id) {
      var self = this;

      // If the sound hasn't loaded, add it to the load queue to pause when capable.
      if (self._state !== 'loaded') {
        self._queue.push({
          event: 'pause',
          action: function() {
            self.pause(id);
          }
        });

        return self;
      }

      // If no id is passed, get all ID's to be paused.
      var ids = self._getSoundIds(id);

      for (var i=0; i<ids.length; i++) {
        // Clear the end timer.
        self._clearTimer(ids[i]);

        // Get the sound.
        var sound = self._soundById(ids[i]);

        if (sound && !sound._paused) {
          // Reset the seek position.
          sound._seek = self.seek(ids[i]);
          sound._rateSeek = 0;
          sound._paused = true;

          // Stop currently running fades.
          self._stopFade(ids[i]);

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

              if (typeof sound._node.bufferSource.stop === 'undefined') {
                sound._node.bufferSource.noteOff(0);
              } else {
                sound._node.bufferSource.stop(0);
              }

              // Clean up the buffer source.
              self._cleanBuffer(sound._node);
            } else if (!isNaN(sound._node.duration) || sound._node.duration === Infinity) {
              sound._node.pause();
            }
          }
        }

        // Fire the pause event, unless `true` is passed as the 2nd argument.
        if (!arguments[1]) {
          self._emit('pause', sound ? sound._id : null);
        }
      }

      return self;
    },

    /**
     * Stop playback and reset to start.
     * @param  {Number} id The sound ID (empty to stop all in group).
     * @param  {Boolean} internal Internal Use: true prevents event firing.
     * @return {Howl}
     */
    stop: function(id, internal) {
      var self = this;

      // If the sound hasn't loaded, add it to the load queue to stop when capable.
      if (self._state !== 'loaded') {
        self._queue.push({
          event: 'stop',
          action: function() {
            self.stop(id);
          }
        });

        return self;
      }

      // If no id is passed, get all ID's to be stopped.
      var ids = self._getSoundIds(id);

      for (var i=0; i<ids.length; i++) {
        // Clear the end timer.
        self._clearTimer(ids[i]);

        // Get the sound.
        var sound = self._soundById(ids[i]);

        if (sound) {
          // Reset the seek position.
          sound._seek = sound._start || 0;
          sound._rateSeek = 0;
          sound._paused = true;
          sound._ended = true;

          // Stop currently running fades.
          self._stopFade(ids[i]);

          if (sound._node) {
            if (self._webAudio) {
              // make sure the sound has been created
              if (!sound._node.bufferSource) {
                if (!internal) {
                  self._emit('stop', sound._id);
                }

                return self;
              }

              if (typeof sound._node.bufferSource.stop === 'undefined') {
                sound._node.bufferSource.noteOff(0);
              } else {
                sound._node.bufferSource.stop(0);
              }

              // Clean up the buffer source.
              self._cleanBuffer(sound._node);
            } else if (!isNaN(sound._node.duration) || sound._node.duration === Infinity) {
              sound._node.currentTime = sound._start || 0;
              sound._node.pause();
            }
          }
        }

        if (sound && !internal) {
          self._emit('stop', sound._id);
        }
      }

      return self;
    },

    /**
     * Mute/unmute a single sound or all sounds in this Howl group.
     * @param  {Boolean} muted Set to true to mute and false to unmute.
     * @param  {Number} id    The sound ID to update (omit to mute/unmute all).
     * @return {Howl}
     */
    mute: function(muted, id) {
      var self = this;

      // If the sound hasn't loaded, add it to the load queue to mute when capable.
      if (self._state !== 'loaded') {
        self._queue.push({
          event: 'mute',
          action: function() {
            self.mute(muted, id);
          }
        });

        return self;
      }

      // If applying mute/unmute to all sounds, update the group's value.
      if (typeof id === 'undefined') {
        if (typeof muted === 'boolean') {
          self._muted = muted;
        } else {
          return self._muted;
        }
      }

      // If no id is passed, get all ID's to be muted.
      var ids = self._getSoundIds(id);

      for (var i=0; i<ids.length; i++) {
        // Get the sound.
        var sound = self._soundById(ids[i]);

        if (sound) {
          sound._muted = muted;

          if (self._webAudio && sound._node) {
            sound._node.gain.setValueAtTime(muted ? 0 : sound._volume, Howler.ctx.currentTime);
          } else if (sound._node) {
            sound._node.muted = Howler._muted ? true : muted;
          }

          self._emit('mute', sound._id);
        }
      }

      return self;
    },

    /**
     * Get/set the volume of this sound or of the Howl group. This method can optionally take 0, 1 or 2 arguments.
     *   volume() -> Returns the group's volume value.
     *   volume(id) -> Returns the sound id's current volume.
     *   volume(vol) -> Sets the volume of all sounds in this Howl group.
     *   volume(vol, id) -> Sets the volume of passed sound id.
     * @return {Howl/Number} Returns self or current volume.
     */
    volume: function() {
      var self = this;
      var args = arguments;
      var vol, id;

      // Determine the values based on arguments.
      if (args.length === 0) {
        // Return the value of the groups' volume.
        return self._volume;
      } else if (args.length === 1 || args.length === 2 && typeof args[1] === 'undefined') {
        // First check if this is an ID, and if not, assume it is a new volume.
        var ids = self._getSoundIds();
        var index = ids.indexOf(args[0]);
        if (index >= 0) {
          id = parseInt(args[0], 10);
        } else {
          vol = parseFloat(args[0]);
        }
      } else if (args.length >= 2) {
        vol = parseFloat(args[0]);
        id = parseInt(args[1], 10);
      }

      // Update the volume or return the current volume.
      var sound;
      if (typeof vol !== 'undefined' && vol >= 0 && vol <= 1) {
        // If the sound hasn't loaded, add it to the load queue to change volume when capable.
        if (self._state !== 'loaded') {
          self._queue.push({
            event: 'volume',
            action: function() {
              self.volume.apply(self, args);
            }
          });

          return self;
        }

        // Set the group volume.
        if (typeof id === 'undefined') {
          self._volume = vol;
        }

        // Update one or all volumes.
        id = self._getSoundIds(id);
        for (var i=0; i<id.length; i++) {
          // Get the sound.
          sound = self._soundById(id[i]);

          if (sound) {
            sound._volume = vol;

            // Stop currently running fades.
            if (!args[2]) {
              self._stopFade(id[i]);
            }

            if (self._webAudio && sound._node && !sound._muted) {
              sound._node.gain.setValueAtTime(vol, Howler.ctx.currentTime);
            } else if (sound._node && !sound._muted) {
              sound._node.volume = vol * Howler.volume();
            }

            self._emit('volume', sound._id);
          }
        }
      } else {
        sound = id ? self._soundById(id) : self._sounds[0];
        return sound ? sound._volume : 0;
      }

      return self;
    },

    /**
     * Fade a currently playing sound between two volumes (if no id is passsed, all sounds will fade).
     * @param  {Number} from The value 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  {Number} id   The sound id (omit to fade all sounds).
     * @return {Howl}
     */
    fade: function(from, to, len, id) {
      var self = this;
      var diff = Math.abs(from - to);
      var dir = from > to ? 'out' : 'in';
      var steps = diff / 0.01;
      var stepLen = (steps > 0) ? len / steps : len;

      // Since browsers clamp timeouts to 4ms, we need to clamp our steps to that too.
      if (stepLen < 4) {
        steps = Math.ceil(steps / (4 / stepLen));
        stepLen = 4;
      }

      // If the sound hasn't loaded, add it to the load queue to fade when capable.
      if (self._state !== 'loaded') {
        self._queue.push({
          event: 'fade',
          action: function() {
            self.fade(from, to, len, id);
          }
        });

        return self;
      }

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

      // Fade the volume of one or all sounds.
      var ids = self._getSoundIds(id);
      for (var i=0; i<ids.length; i++) {
        // Get the sound.
        var sound = self._soundById(ids[i]);

        // Create a linear fade or fall back to timeouts with HTML5 Audio.
        if (sound) {
          // Stop the previous fade if no sprite is being used (otherwise, volume handles this).
          if (!id) {
            self._stopFade(ids[i]);
          }

          // If we are using Web Audio, let the native methods do the actual fade.
          if (self._webAudio && !sound._muted) {
            var currentTime = Howler.ctx.currentTime;
            var end = currentTime + (len / 1000);
            sound._volume = from;
            sound._node.gain.setValueAtTime(from, currentTime);
            sound._node.gain.linearRampToValueAtTime(to, end);
          }

          var vol = from;
          sound._interval = setInterval(function(soundId, sound) {
            // Update the volume amount, but only if the volume should change.
            if (steps > 0) {
              vol += (dir === 'in' ? 0.01 : -0.01);
            }

            // Make sure the volume is in the right bounds.
            vol = Math.max(0, vol);
            vol = Math.min(1, vol);

            // Round to within 2 decimal points.
            vol = Math.round(vol * 100) / 100;

            // Change the volume.
            if (self._webAudio) {
              if (typeof id === 'undefined') {
                self._volume = vol;
              }

              sound._volume = vol;
            } else {
              self.volume(vol, soundId, true);
            }

            // When the fade is complete, stop it and fire event.
            if (vol === to) {
              clearInterval(sound._interval);
              sound._interval = null;
              self.volume(vol, soundId);
              self._emit('fade', soundId);
            }
          }.bind(self, ids[i], sound), stepLen);
        }
      }

      return self;
    },

    /**
     * Internal method that stops the currently playing fade when
     * a new fade starts, volume is changed or the sound is stopped.
     * @param  {Number} id The sound id.
     * @return {Howl}
     */
    _stopFade: function(id) {
      var self = this;
      var sound = self._soundById(id);

      if (sound && sound._interval) {
        if (self._webAudio) {
          sound._node.gain.cancelScheduledValues(Howler.ctx.currentTime);
        }

        clearInterval(sound._interval);
        sound._interval = null;
        self._emit('fade', id);
      }

      return self;
    },

    /**
     * Get/set the loop parameter on a sound. This method can optionally take 0, 1 or 2 arguments.
     *   loop() -> Returns the group's loop value.
     *   loop(id) -> Returns the sound id's loop value.
     *   loop(loop) -> Sets the loop value for all sounds in this Howl group.
     *   loop(loop, id) -> Sets the loop value of passed sound id.
     * @return {Howl/Boolean} Returns self or current loop value.
     */
    loop: function() {
      var self = this;
      var args = arguments;
      var loop, id, sound;

      // Determine the values for loop and id.
      if (args.length === 0) {
        // Return the grou's loop value.
        return self._loop;
      } else if (args.length === 1) {
        if (typeof args[0] === 'boolean') {
          loop = args[0];
          self._loop = loop;
        } else {
          // Return this sound's loop value.
          sound = self._soundById(parseInt(args[0], 10));
          return sound ? sound._loop : false;
        }
      } else if (args.length === 2) {
        loop = args[0];
        id = parseInt(args[1], 10);
      }

      // If no id is passed, get all ID's to be looped.
      var ids = self._getSoundIds(id);
      for (var i=0; i<ids.length; i++) {
        sound = self._soundById(ids[i]);

        if (sound) {
          sound._loop = loop;
          if (self._webAudio && sound._node && sound._node.bufferSource) {
            sound._node.bufferSource.loop = loop;
            if (loop) {
              sound._node.bufferSource.loopStart = sound._start || 0;
              sound._node.bufferSource.loopEnd = sound._stop;
            }
          }
        }
      }

      return self;
    },

    /**
     * Get/set the playback rate of a sound. This method can optionally take 0, 1 or 2 arguments.
     *   rate() -> Returns the first sound node's current playback rate.
     *   rate(id) -> Returns the sound id's current playback rate.
     *   rate(rate) -> Sets the playback rate of all sounds in this Howl group.
     *   rate(rate, id) -> Sets the playback rate of passed sound id.
     * @return {Howl/Number} Returns self or the current playback rate.
     */
    rate: function() {
      var self = this;
      var args = arguments;
      var rate, id;

      // Determine the values based on arguments.
      if (args.length === 0) {
        // We will simply return the current rate of the first node.
        id = self._sounds[0]._id;
      } else if (args.length === 1) {
        // First check if this is an ID, and if not, assume it is a new rate value.
        var ids = self._getSoundIds();
        var index = ids.indexOf(args[0]);
        if (index >= 0) {
          id = parseInt(args[0], 10);
        } else {
          rate = parseFloat(args[0]);
        }
      } else if (args.length === 2) {
        rate = parseFloat(args[0]);
        id = parseInt(args[1], 10);
      }

      // Update the playback rate or return the current value.
      var sound;
      if (typeof rate === 'number') {
        // If the sound hasn't loaded, add it to the load queue to change playback rate when capable.
        if (self._state !== 'loaded') {
          self._queue.push({
            event: 'rate',
            action: function() {
              self.rate.apply(self, args);
            }
          });

          return self;
        }

        // Set the group rate.
        if (typeof id === 'undefined') {
          self._rate = rate;
        }

        // Update one or all volumes.
        id = self._getSoundIds(id);
        for (var i=0; i<id.length; i++) {
          // Get the sound.
          sound = self._soundById(id[i]);

          if (sound) {
            // Keep track of our position when the rate changed and update the playback
            // start position so we can properly adjust the seek position for time elapsed.
            sound._rateSeek = self.seek(id[i]);
            sound._playStart = self._webAudio ? Howler.ctx.currentTime : sound._playStart;
            sound._rate = rate;

            // Change the playback rate.
            if (self._webAudio && sound._node && sound._node.bufferSource) {
              sound._node.bufferSource.playbackRate.value = rate;
            } else if (sound._node) {
              sound._node.playbackRate = rate;
            }

            // Reset the timers.
            var seek = self.seek(id[i]);
            var duration = ((self._sprite[sound._sprite][0] + self._sprite[sound._sprite][1]) / 1000) - seek;
            var timeout = (duration * 1000) / Math.abs(sound._rate);

            // Start a new end timer if sound is already playing.
            if (self._endTimers[id[i]] || !sound._paused) {
              self._clearTimer(id[i]);
              self._endTimers[id[i]] = setTimeout(self._ended.bind(self, sound), timeout);
            }

            self._emit('rate', sound._id);
          }
        }
      } else {
        sound = self._soundById(id);
        return sound ? sound._rate : self._rate;
      }

      return self;
    },

    /**
     * Get/set the seek position of a sound. This method can optionally take 0, 1 or 2 arguments.
     *   seek() -> Returns the first sound node's current seek position.
     *   seek(id) -> Returns the sound id's current seek position.
     *   seek(seek) -> Sets the seek position of the first sound node.
     *   seek(seek, id) -> Sets the seek position of passed sound id.
     * @return {Howl/Number} Returns self or the current seek position.
     */
    seek: function() {
      var self = this;
      var args = arguments;
      var seek, id;

      // Determine the values based on arguments.
      if (args.length === 0) {
        // We will simply return the current position of the first node.
        id = self._sounds[0]._id;
      } else if (args.length === 1) {
        // First check if this is an ID, and if not, assume it is a new seek position.
        var ids = self._getSoundIds();
        var index = ids.indexOf(args[0]);
        if (index >= 0) {
          id = parseInt(args[0], 10);
        } else {
          id = self._sounds[0]._id;
          seek = parseFloat(args[0]);
        }
      } else if (args.length === 2) {
        seek = parseFloat(args[0]);
        id = parseInt(args[1], 10);
      }

      // If there is no ID, bail out.
      if (typeof id === 'undefined') {
        return self;
      }

      // If the sound hasn't loaded, add it to the load queue to seek when capable.
      if (self._state !== 'loaded') {
        self._queue.push({
          event: 'seek',
          action: function() {
            self.seek.apply(self, args);
          }
        });

        return self;
      }

      // Get the sound.
      var sound = self._soundById(id);

      if (sound) {
        if (typeof seek === 'number' && seek >= 0) {
          // Pause the sound and update position for restarting playback.
          var playing = self.playing(id);
          if (playing) {
            self.pause(id, true);
          }

          // Move the position of the track and cancel timer.
          sound._seek = seek;
          sound._ended = false;
          self._clearTimer(id);

          // Restart the playback if the sound was playing.
          if (playing) {
            self.play(id, true);
          }

          // Update the seek position for HTML5 Audio.
          if (!self._webAudio && sound._node) {
            sound._node.currentTime = seek;
          }

          self._emit('seek', id);
        } else {
          if (self._webAudio) {
            var realTime = self.playing(id) ? Howler.ctx.currentTime - sound._playStart : 0;
            var rateSeek = sound._rateSeek ? sound._rateSeek - sound._seek : 0;
            return sound._seek + (rateSeek + realTime * Math.abs(sound._rate));
          } else {
            return sound._node.currentTime;
          }
        }
      }

      return self;
    },

    /**
     * Check if a specific sound is currently playing or not (if id is provided), or check if at least one of the sounds in the group is playing or not.
     * @param  {Number}  id The sound id to check. If none is passed, the whole sound group is checked.
     * @return {Boolean} True if playing and false if not.
     */
    playing: function(id) {
      var self = this;

      // Check the passed sound ID (if any).
      if (typeof id === 'number') {
        var sound = self._soundById(id);
        return sound ? !sound._paused : false;
      }

      // Otherwise, loop through all sounds and check if any are playing.
      for (var i=0; i<self._sounds.length; i++) {
        if (!self._sounds[i]._paused) {
          return true;
        }
      }

      return false;
    },

    /**
     * Get the duration of this sound. Passing a sound id will return the sprite duration.
     * @param  {Number} id The sound id to check. If none is passed, return full source duration.
     * @return {Number} Audio duration in seconds.
     */
    duration: function(id) {
      var self = this;
      var duration = self._duration;

      // If we pass an ID, get the sound and return the sprite length.
      var sound = self._soundById(id);
      if (sound) {
        duration = self._sprite[sound._sprite][1] / 1000;
      }

      return duration;
    },

    /**
     * Returns the current loaded state of this Howl.
     * @return {String} 'unloaded', 'loading', 'loaded'
     */
    state: function() {
      return this._state;
    },

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

      // Stop playing any active sounds.
      var sounds = self._sounds;
      for (var i=0; i<sounds.length; i++) {
        // Stop the sound if it is currently playing.
        if (!sounds[i]._paused) {
          self.stop(sounds[i]._id);
          self._emit('end', sounds[i]._id);
        }

        // Remove the source or disconnect.
        if (!self._webAudio) {
          // Set the source to 0-second silence to stop any downloading.
          sounds[i]._node.src = 'data:audio/wav;base64,UklGRiQAAABXQVZFZm10IBAAAAABAAEARKwAAIhYAQACABAAZGF0YQAAAAA=';

          // Remove any event listeners.
          sounds[i]._node.removeEventListener('error', sounds[i]._errorFn, false);
          sounds[i]._node.removeEventListener(Howler._canPlayEvent, sounds[i]._loadFn, false);
        }

        // Empty out all of the nodes.
        delete sounds[i]._node;

        // Make sure all timers are cleared out.
        self._clearTimer(sounds[i]._id);

        // Remove the references in the global Howler object.
        var index = Howler._howls.indexOf(self);
        if (index >= 0) {
          Howler._howls.splice(index, 1);
        }
      }

      // Delete this sound from the cache (if no other Howl is using it).
      var remCache = true;
      for (i=0; i<Howler._howls.length; i++) {
        if (Howler._howls[i]._src === self._src) {
          remCache = false;
          break;
        }
      }

      if (cache && remCache) {
        delete cache[self._src];
      }

      // Clear global errors.
      Howler.noAudio = false;

      // Clear out `self`.
      self._state = 'unloaded';
      self._sounds = [];
      self = null;

      return null;
    },

    /**
     * Listen to a custom event.
     * @param  {String}   event Event name.
     * @param  {Function} fn    Listener to call.
     * @param  {Number}   id    (optional) Only listen to events for this sound.
     * @param  {Number}   once  (INTERNAL) Marks event to fire only once.
     * @return {Howl}
     */
    on: function(event, fn, id, once) {
      var self = this;
      var events = self['_on' + event];

      if (typeof fn === 'function') {
        events.push(once ? {id: id, fn: fn, once: once} : {id: id, fn: fn});
      }

      return self;
    },

    /**
     * Remove a custom event. Call without parameters to remove all events.
     * @param  {String}   event Event name.
     * @param  {Function} fn    Listener to remove. Leave empty to remove all.
     * @param  {Number}   id    (optional) Only remove events for this sound.
     * @return {Howl}
     */
    off: function(event, fn, id) {
      var self = this;
      var events = self['_on' + event];
      var i = 0;

      if (fn) {
        // Loop through event store and remove the passed function.
        for (i=0; i<events.length; i++) {
          if (fn === events[i].fn && id === events[i].id) {
            events.splice(i, 1);
            break;
          }
        }
      } else if (event) {
        // Clear out all events of this type.
        self['_on' + event] = [];
      } else {
        // Clear out all events of every type.
        var keys = Object.keys(self);
        for (i=0; i<keys.length; i++) {
          if ((keys[i].indexOf('_on') === 0) && Array.isArray(self[keys[i]])) {
            self[keys[i]] = [];
          }
        }
      }

      return self;
    },

    /**
     * Listen to a custom event and remove it once fired.
     * @param  {String}   event Event name.
     * @param  {Function} fn    Listener to call.
     * @param  {Number}   id    (optional) Only listen to events for this sound.
     * @return {Howl}
     */
    once: function(event, fn, id) {
      var self = this;

      // Setup the event listener.
      self.on(event, fn, id, 1);

      return self;
    },

    /**
     * Emit all events of a specific type and pass the sound id.
     * @param  {String} event Event name.
     * @param  {Number} id    Sound ID.
     * @param  {Number} msg   Message to go with event.
     * @return {Howl}
     */
    _emit: function(event, id, msg) {
      var self = this;
      var events = self['_on' + event];

      // Loop through event store and fire all functions.
      for (var i=events.length-1; i>=0; i--) {
        if (!events[i].id || events[i].id === id || event === 'load') {
          setTimeout(function(fn) {
            fn.call(this, id, msg);
          }.bind(self, events[i].fn), 0);

          // If this event was setup with `once`, remove it.
          if (events[i].once) {
            self.off(event, events[i].fn, events[i].id);
          }
        }
      }

      return self;
    },

    /**
     * Queue of actions initiated before the sound has loaded.
     * These will be called in sequence, with the next only firing
     * after the previous has finished executing (even if async like play).
     * @return {Howl}
     */
    _loadQueue: function() {
      var self = this;

      if (self._queue.length > 0) {
        var task = self._queue[0];

        // don't move onto the next task until this one is done
        self.once(task.event, function() {
          self._queue.shift();
          self._loadQueue();
        });

        task.action();
      }

      return self;
    },

    /**
     * Fired when playback ends at the end of the duration.
     * @param  {Sound} sound The sound object to work with.
     * @return {Howl}
     */
    _ended: function(sound) {
      var self = this;
      var sprite = sound._sprite;

      // Should this sound loop?
      var loop = !!(sound._loop || self._sprite[sprite][2]);

      // Fire the ended event.
      self._emit('end', sound._id);

      // Restart the playback for HTML5 Audio loop.
      if (!self._webAudio && loop) {
        self.stop(sound._id, true).play(sound._id);
      }

      // Restart this timer if on a Web Audio loop.
      if (self._webAudio && loop) {
        self._emit('play', sound._id);
        sound._seek = sound._start || 0;
        sound._rateSeek = 0;
        sound._playStart = Howler.ctx.currentTime;

        var timeout = ((sound._stop - sound._start) * 1000) / Math.abs(sound._rate);
        self._endTimers[sound._id] = setTimeout(self._ended.bind(self, sound), timeout);
      }

      // Mark the node as paused.
      if (self._webAudio && !loop) {
        sound._paused = true;
        sound._ended = true;
        sound._seek = sound._start || 0;
        sound._rateSeek = 0;
        self._clearTimer(sound._id);

        // Clean up the buffer source.
        self._cleanBuffer(sound._node);

        // Attempt to auto-suspend AudioContext if no sounds are still playing.
        Howler._autoSuspend();
      }

      // When using a sprite, end the track.
      if (!self._webAudio && !loop) {
        self.stop(sound._id);
      }

      return self;
    },

    /**
     * Clear the end timer for a sound playback.
     * @param  {Number} id The sound ID.
     * @return {Howl}
     */
    _clearTimer: function(id) {
      var self = this;

      if (self._endTimers[id]) {
        clearTimeout(self._endTimers[id]);
        delete self._endTimers[id];
      }

      return self;
    },

    /**
     * Return the sound identified by this ID, or return null.
     * @param  {Number} id Sound ID
     * @return {Object}    Sound object or null.
     */
    _soundById: function(id) {
      var self = this;

      // Loop through all sounds and find the one with this ID.
      for (var i=0; i<self._sounds.length; i++) {
        if (id === self._sounds[i]._id) {
          return self._sounds[i];
        }
      }

      return null;
    },

    /**
     * Return an inactive sound from the pool or create a new one.
     * @return {Sound} Sound playback object.
     */
    _inactiveSound: function() {
      var self = this;

      self._drain();

      // Find the first inactive node to recycle.
      for (var i=0; i<self._sounds.length; i++) {
        if (self._sounds[i]._ended) {
          return self._sounds[i].reset();
        }
      }

      // If no inactive node was found, create a new one.
      return new Sound(self);
    },

    /**
     * Drain excess inactive sounds from the pool.
     */
    _drain: function() {
      var self = this;
      var limit = self._pool;
      var cnt = 0;
      var i = 0;

      // If there are less sounds than the max pool size, we are done.
      if (self._sounds.length < limit) {
        return;
      }

      // Count the number of inactive sounds.
      for (i=0; i<self._sounds.length; i++) {
        if (self._sounds[i]._ended) {
          cnt++;
        }
      }

      // Remove excess inactive sounds, going in reverse order.
      for (i=self._sounds.length - 1; i>=0; i--) {
        if (cnt <= limit) {
          return;
        }

        if (self._sounds[i]._ended) {
          // Disconnect the audio source when using Web Audio.
          if (self._webAudio && self._sounds[i]._node) {
            self._sounds[i]._node.disconnect(0);
          }

          // Remove sounds until we have the pool size.
          self._sounds.splice(i, 1);
          cnt--;
        }
      }
    },

    /**
     * Get all ID's from the sounds pool.
     * @param  {Number} id Only return one ID if one is passed.
     * @return {Array}    Array of IDs.
     */
    _getSoundIds: function(id) {
      var self = this;

      if (typeof id === 'undefined') {
        var ids = [];
        for (var i=0; i<self._sounds.length; i++) {
          ids.push(self._sounds[i]._id);
        }

        return ids;
      } else {
        return [id];
      }
    },

    /**
     * Load the sound back into the buffer source.
     * @param  {Sound} sound The sound object to work with.
     * @return {Howl}
     */
    _refreshBuffer: function(sound) {
      var self = this;

      // Setup the buffer source for playback.
      sound._node.bufferSource = Howler.ctx.createBufferSource();
      sound._node.bufferSource.buffer = cache[self._src];

      // Connect to the correct node.
      if (sound._panner) {
        sound._node.bufferSource.connect(sound._panner);
      } else {
        sound._node.bufferSource.connect(sound._node);
      }

      // Setup looping and playback rate.
      sound._node.bufferSource.loop = sound._loop;
      if (sound._loop) {
        sound._node.bufferSource.loopStart = sound._start || 0;
        sound._node.bufferSource.loopEnd = sound._stop;
      }
      sound._node.bufferSource.playbackRate.value = sound._rate;

      return self;
    },

    /**
     * Prevent memory leaks by cleaning up the buffer source after playback.
     * @param  {Object} node Sound's audio node containing the buffer source.
     * @return {Howl}
     */
    _cleanBuffer: function(node) {
      var self = this;

      if (self._scratchBuffer) {
        node.bufferSource.onended = null;
        node.bufferSource.disconnect(0);
        try { node.bufferSource.buffer = self._scratchBuffer; } catch(e) {}
      }
      node.bufferSource = null;

      return self;
    }
  };

  /** Single Sound Methods **/
  /***************************************************************************/

  /**
   * Setup the sound object, which each node attached to a Howl group is contained in.
   * @param {Object} howl The Howl parent group.
   */
  var Sound = function(howl) {
    this._parent = howl;
    this.init();
  };
  Sound.prototype = {
    /**
     * Initialize a new Sound object.
     * @return {Sound}
     */
    init: function() {
      var self = this;
      var parent = self._parent;

      // Setup the default parameters.
      self._muted = parent._muted;
      self._loop = parent._loop;
      self._volume = parent._volume;
      self._muted = parent._muted;
      self._rate = parent._rate;
      self._seek = 0;
      self._paused = true;
      self._ended = true;
      self._sprite = '__default';

      // Generate a unique ID for this sound.
      self._id = Math.round(Date.now() * Math.random());

      // Add itself to the parent's pool.
      parent._sounds.push(self);

      // Create the new node.
      self.create();

      return self;
    },

    /**
     * Create and setup a new sound object, whether HTML5 Audio or Web Audio.
     * @return {Sound}
     */
    create: function() {
      var self = this;
      var parent = self._parent;
      var volume = (Howler._muted || self._muted || self._parent._muted) ? 0 : self._volume;

      if (parent._webAudio) {
        // Create the gain node for controlling volume (the source will connect to this).
        self._node = (typeof Howler.ctx.createGain === 'undefined') ? Howler.ctx.createGainNode() : Howler.ctx.createGain();
        self._node.gain.setValueAtTime(volume, Howler.ctx.currentTime);
        self._node.paused = true;
        self._node.connect(Howler.masterGain);
      } else {
        self._node = new Audio();

        // Listen for errors (http://dev.w3.org/html5/spec-author-view/spec.html#mediaerror).
        self._errorFn = self._errorListener.bind(self);
        self._node.addEventListener('error', self._errorFn, false);

        // Listen for 'canplaythrough' event to let us know the sound is ready.
        self._loadFn = self._loadListener.bind(self);
        self._node.addEventListener(Howler._canPlayEvent, self._loadFn, false);

        // Setup the new audio node.
        self._node.src = parent._src;
        self._node.preload = 'auto';
        self._node.volume = volume * Howler.volume();

        // Begin loading the source.
        self._node.load();
      }

      return self;
    },

    /**
     * Reset the parameters of this sound to the original state (for recycle).
     * @return {Sound}
     */
    reset: function() {
      var self = this;
      var parent = self._parent;

      // Reset all of the parameters of this sound.
      self._muted = parent._muted;
      self._loop = parent._loop;
      self._volume = parent._volume;
      self._muted = parent._muted;
      self._rate = parent._rate;
      self._seek = 0;
      self._rateSeek = 0;
      self._paused = true;
      self._ended = true;
      self._sprite = '__default';

      // Generate a new ID so that it isn't confused with the previous sound.
      self._id = Math.round(Date.now() * Math.random());

      return self;
    },

    /**
     * HTML5 Audio error listener callback.
     */
    _errorListener: function() {
      var self = this;

      // Fire an error event and pass back the code.
      self._parent._emit('loaderror', self._id, self._node.error ? self._node.error.code : 0);

      // Clear the event listener.
      self._node.removeEventListener('error', self._errorListener, false);
    },

    /**
     * HTML5 Audio canplaythrough listener callback.
     */
    _loadListener: function() {
      var self = this;
      var parent = self._parent;

      // Round up the duration to account for the lower precision in HTML5 Audio.
      parent._duration = Math.ceil(self._node.duration * 10) / 10;

      // Setup a sprite if none is defined.
      if (Object.keys(parent._sprite).length === 0) {
        parent._sprite = {__default: [0, parent._duration * 1000]};
      }

      if (parent._state !== 'loaded') {
        parent._state = 'loaded';
        parent._emit('load');
        parent._loadQueue();
      }

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

      // Clear the event listener.
      self._node.removeEventListener(Howler._canPlayEvent, self._loadFn, false);
    }
  };

  /** Helper Methods **/
  /***************************************************************************/

  var cache = {};

  /**
   * Buffer a sound from URL, Data URI or cache and decode to audio source (Web Audio API).
   * @param  {Howl} self
   */
  var loadBuffer = function(self) {
    var url = self._src;

    // Check if the buffer has already been cached and use it instead.
    if (cache[url]) {
      // Set the duration from the cache.
      self._duration = cache[url].duration;

      // Load the sound into this Howl.
      loadSound(self);

      return;
    }

    if (/^data:[^;]+;base64,/.test(url)) {
      // Decode the base64 data URI without XHR, since some browsers don't support it.
      var data = atob(url.split(',')[1]);
      var dataView = new Uint8Array(data.length);
      for (var i=0; i<data.length; ++i) {
        dataView[i] = data.charCodeAt(i);
      }

      decodeAudioData(dataView.buffer, self);
    } else {
      // Load the buffer from the URL.
      var xhr = new XMLHttpRequest();
      xhr.open('GET', url, true);
      xhr.responseType = 'arraybuffer';
      xhr.onload = function() {
        // Make sure we get a successful response back.
        var code = (xhr.status + '')[0];
        if (code !== '0' && code !== '2' && code !== '3') {
          self._emit('loaderror', null, 'Failed loading audio file with status: ' + xhr.status + '.');
          return;
        }

        decodeAudioData(xhr.response, self);
      };
      xhr.onerror = function() {
        // If there is an error, switch to HTML5 Audio.
        if (self._webAudio) {
          self._html5 = true;
          self._webAudio = false;
          self._sounds = [];
          delete cache[url];
          self.load();
        }
      };
      safeXhrSend(xhr);
    }
  };

  /**
   * Send the XHR request wrapped in a try/catch.
   * @param  {Object} xhr XHR to send.
   */
  var safeXhrSend = function(xhr) {
    try {
      xhr.send();
    } catch (e) {
      xhr.onerror();
    }
  };

  /**
   * Decode audio data from an array buffer.
   * @param  {ArrayBuffer} arraybuffer The audio data.
   * @param  {Howl}        self
   */
  var decodeAudioData = function(arraybuffer, self) {
    // Decode the buffer into an audio source.
    Howler.ctx.decodeAudioData(arraybuffer, function(buffer) {
      if (buffer && self._sounds.length > 0) {
        cache[self._src] = buffer;
        loadSound(self, buffer);
      }
    }, function() {
      self._emit('loaderror', null, 'Decoding audio data failed.');
    });
  };

  /**
   * Sound is now loaded, so finish setting everything up and fire the loaded event.
   * @param  {Howl} self
   * @param  {Object} buffer The decoded buffer sound source.
   */
  var loadSound = function(self, buffer) {
    // Set the duration.
    if (buffer && !self._duration) {
      self._duration = buffer.duration;
    }

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

    // Fire the loaded event.
    if (self._state !== 'loaded') {
      self._state = 'loaded';
      self._emit('load');
      self._loadQueue();
    }

    // Begin playback if specified.
    if (self._autoplay) {
      self.play();
    }
  };

  /**
   * Setup the audio context when available, or switch to HTML5 Audio mode.
   */
  var setupAudioContext = function() {
    // Check if we are using Web Audio and setup the AudioContext if we are.
    try {
      if (typeof AudioContext !== 'undefined') {
        Howler.ctx = new AudioContext();
      } else if (typeof webkitAudioContext !== 'undefined') {
        Howler.ctx = new webkitAudioContext();
      } else {
        Howler.usingWebAudio = false;
      }
    } catch(e) {
      Howler.usingWebAudio = false;
    }

    // Check if a webview is being used on iOS8 or earlier (rather than the browser).
    // If it is, disable Web Audio as it causes crashing.
    var iOS = (/iP(hone|od|ad)/.test(Howler._navigator && Howler._navigator.platform));
    var appVersion = Howler._navigator && Howler._navigator.appVersion.match(/OS (\d+)_(\d+)_?(\d+)?/);
    var version = appVersion ? parseInt(appVersion[1], 10) : null;
    if (iOS && version && version < 9) {
      var safari = /safari/.test(Howler._navigator && Howler._navigator.userAgent.toLowerCase());
      if (Howler._navigator && Howler._navigator.standalone && !safari || Howler._navigator && !Howler._navigator.standalone && !safari) {
        Howler.usingWebAudio = false;
      }
    }

    // Create and expose the master GainNode when using Web Audio (useful for plugins or advanced usage).
    if (Howler.usingWebAudio) {
      Howler.masterGain = (typeof Howler.ctx.createGain === 'undefined') ? Howler.ctx.createGainNode() : Howler.ctx.createGain();
      Howler.masterGain.gain.value = 1;
      Howler.masterGain.connect(Howler.ctx.destination);
    }

    // Re-run the setup on Howler.
    Howler._setup();
  };

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

  // Add support for CommonJS libraries such as browserify.
  if (typeof exports !== 'undefined') {
    exports.Howler = Howler;
    exports.Howl = Howl;
  }

  // Define globally in case AMD is not available or unused.
  if (typeof window !== 'undefined') {
    window.HowlerGlobal = HowlerGlobal;
    window.Howler = Howler;
    window.Howl = Howl;
    window.Sound = Sound;
  } else if (typeof global !== 'undefined') { // Add to global in Node.js (for testing, etc).
    global.HowlerGlobal = HowlerGlobal;
    global.Howler = Howler;
    global.Howl = Howl;
    global.Sound = Sound;
  }
})();