How can I fade in and fade out audio in just_audio?

Question

I have a ConcatenatingAudioSource for which I want to fade each item in and out. What is the best way to fade in and fade out in just_audio?

Answer 1

As per @Intellect's comment, I achieved a fade out effect by just controlling the volume with a CountdownTimer. Here is an example in an AudioManager class I set up that does the trick, FYI.

import 'package:just_audio/just_audio.dart';
import 'package:quiver/async.dart';

class AudioManager {

/// Relevant code snippets ....

  final AudioPlayer _player = AudioPlayer();
  CountdownTimer? _timer;

  Future<void> play({required String audio, required volume}) async {
    _player
        .setAsset('assets/audio/$audio.mp3')
        .then((value) async {
       

      /// Stop the [_player] and important to cancel the [_timer].
      /// If audio is switched, and the [_timer] is not cancelled, it will continue to run and 
      /// may cancel the new clip.
      if (_player.playing) {
        _timer?.cancel();
        await _player.stop();
      }
          
          /// Make sure to reset the volume when play another clip.

      await _player.seek(Duration.zero);
      await _player.setVolume(volume);
      await _player.play();
    });
  }

  Future<void> fadeOutAndStop(
      {required double startVolume}) async {
    /// Will fade out over 3 seconds
    Duration duration = const Duration(seconds: 3);

    /// Using a [CountdownTimer] to decrement the volume every 50 milliseconds, then stop [AudioPlayer] when done.
    _timer = CountdownTimer(duration, const Duration(milliseconds: 50))..listen((event) {
      final percent = event.remaining.inMilliseconds / duration.inMilliseconds;
      setVolume(percent * startVolume);
    }).onDone(() async {
      await _player.stop();
    });
  }

  Future<void> setVolume(double volume) async =>
      await _player.setVolume(volume);
  ///
}