AudioSound is an AudioClip scheduled to be played on an AudioSource. You cannot construct an instance of the AudioSound class directly, it can only be done by playing an AudioClip from an AudioSource (See AudioSource, AudioMusic, and AudioManager).

class AudioSound {
 final AudioSource _source;
 final AudioClip _clip;
 final bool _loop;
 AudioBufferSourceNode _sourceNode;
 num _pausedTime;
 num _startTime;
 num _scheduledTime;
 num _volume = 1.0;

 /** Is the sound scheduled to be played? */
 bool get isScheduled => _sourceNode == null ? false : _sourceNode.playbackState == AudioBufferSourceNode.SCHEDULED_STATE;
 /** Is the sound playing right now? */
 bool get isPlaying => _sourceNode == null ? false : _sourceNode.playbackState == AudioBufferSourceNode.PLAYING_STATE;
 /** Is the sound finished being played? */
 bool get isFinished => _sourceNode == null ? false : _sourceNode.playbackState == AudioBufferSourceNode.FINISHED_STATE;

 AudioSound._internal(this._source, this._clip, this._loop) {
   _setupSourceNodeForPlayback();
 }

 void _dumpSourceNode() {
   if (_sourceNode != null) {
     print('${_sourceNode.playbackState}');
   }
 }

 void _setupSourceNodeForPlayback() {
   _sourceNode = _source._manager._context.createBufferSource();
   if (_clip != null && _clip._buffer != null) {
     _sourceNode.buffer = _clip._buffer;
     _sourceNode.loopStart = 0.0;
     _sourceNode.loopEnd = _clip._buffer.duration;
   }
   _sourceNode.gain.value = _volume;
   _sourceNode.loop = _loop;
   _sourceNode.connect(_source._gainNode, 0, 0);
 }

 void _stop() {
   if (_sourceNode != null) {
     _sourceNode.stop(0.0);
   }
   _sourceNode = null;
 }

 /** Is the sound paused? */
 bool get pause => _pausedTime != null;

 /** Pause or unpause the sound. */
 void set pause(bool b) {
   if (b) {
     if (_pausedTime != null) {
       // Double pause.
       return;
     }
     _pause();
   } else {
     if (_pausedTime == null) {
       // Double unpause.
       return;
     }
     _resume();
   }
 }

 /**
  * Time cursor for sound. Will be negative is sound is scheduled
  * to be played. Positive if playing.
  */
 num get time {
   var now = _source._manager._context.currentTime;
   if (_pausedTime != null) {
     return _pausedTime;
   }
   return _computePausedTime();
 }

 num _computePausedTime() {
   assert(_startTime != null);
   var now = _source._manager._context.currentTime;
   var delta = now - _startTime;
   if (now < _scheduledTime) {
     // Haven't started yet.
     return now-_scheduledTime;
   }
   // Playing sound.
   if (_loop) {
     return delta % _sourceNode.buffer.duration;
   }
   return delta;
 }

 void _pause() {
   if (_startTime == null) {
     // Not started.
     return;
   }
   print('Sound.pause');
   _dumpSourceNode();
   if (_sourceNode != null) {
     _pausedTime = _computePausedTime();
     _stop();
     print('paused at $_pausedTime');
   }
 }

 void _resume() {
   if (_pausedTime == null) {
     // Not paused.
     return;
   }
   print('Sound.resume');
   _dumpSourceNode();
   _setupSourceNodeForPlayback();
   if (_pausedTime < 0.0) {
     // Schedule again.
     _pausedTime = -_pausedTime;
     print('Scheduling to play sound in $_pausedTime.');
     _scheduledTime = _source._manager._context.currentTime+_pausedTime;
     _sourceNode.start(_scheduledTime, 0.0, _sourceNode.buffer.duration);
     _startTime = _source._manager._context.currentTime;
   } else {
     print('Starting to play at offset $_pausedTime');
     _scheduledTime = _source._manager._context.currentTime;
     _sourceNode.start(_scheduledTime, // Now.
                       _pausedTime, // Offset.
                       _sourceNode.buffer.duration-_pausedTime); // Length.
     // Offset the time that start was called by the offset into clip.
     _startTime = _source._manager._context.currentTime-_pausedTime;
   }
   // Clear paused time.
   _pausedTime = null;
 }

 /** Start playing this sound in [when] seconds. */
 void play([num when=0.0]) {
   //print('Sound.play');
   //_dumpSourceNode();
   _stop();
   _setupSourceNodeForPlayback();
   _scheduledTime = _source._manager._context.currentTime+when;
   _sourceNode.start(_scheduledTime);
   // Called start now.
   _startTime = _source._manager._context.currentTime;
 }

 /** Stop playing this sound */
 void stop() {
   _stop();
   _startTime = null;
   _scheduledTime = null;
   _pausedTime = null;
 }

 /** Get the volume of the sound. 0.0 <= volume <= 1.0. */
 num get volume => _volume;

 /** Set the volume for the sound. */
 void set volume(num v) {
   if (_sourceNode != null) {
     _sourceNode.gain.value = v;
   }
   _volume = v;
 }
}