final CacheAudioPlayer audioPlayer = CacheAudioPlayer();

//Always register listeners in order to receive updates from event channel.
audioPlayer.registerListeners();

//Event channel callbacks:
audioPlayer.onStateChanged.listen((AudioPlayerState state) {
  setState(() {
      //or do whatever you need to do with the new state
     _state = state;
  });
});

audioPlayer.onPlayerBuffered.listen((double percentageBuffered) {
  setState(() {
     _bufferedPercentage = percentageBuffered;
  });
});

audioPlayer.onTimeElapsed.listen((double timeInSeconds) {
  setState(() {
      _timeInSeconds = timeInSeconds;
   });
  });

audioPlayer.onError.listen((Object error) {
   setState(() {
      _error = error;
  });
});

audioPlayer.loadUrl("your url");
audioPlayer.play();