Cross fade #237

[BobcatNoah]

This PR is work in progress and will implement cross fade #237 between songs. The code is not complete because I want someone to review it before I move forward and there is a major issue I need help with.

I don't have a video example right now, but the issue is that the cross fade is being paused before the seeking is finished. This causes a noticeable gap on slower devices or when the device is connected to something like a car stereo. The expected behavior is that it waits until the seeking is finished before pausing. I suspect this is being caused by a delay between when the seek function finishes (thus returning and letting the code continue) and when the song actually starts playing again.

_player.currentIndexStream.listen((event) async {
        if (_player.processingState == ProcessingState.ready) {
          //fadeIsReady = false;
          _player.setVolume(1);
          if (event != null && nextItem == _getQueueItem(_player.currentIndex?? 0)) {
            await Future.delayed(const Duration(milliseconds: 1));
            //final test = Stopwatch();
            //test.start();
            await _player.seek(_crossFadePlayer.position);
            await Future.delayed(Duration(milliseconds: 15));
            _crossFadePlayer.pause();
            //test.stop();
            //_audioServiceBackgroundTaskLogger.info(test.elapsedMilliseconds);
            //finishedSwitchingSong = true;
          }
        }
      });

Below is a video of expected behavior. This example isn't perfect though due to the issue.

RPReplay_Final1698882594.MP4

[jmshrv]

I believe @Chaphasilor was working on this, they may be able to help :)

[Chaphasilor]

I was not, but my suggestion would be to pause the crossfading player a few seconds later. Maybe fade the volume down again until the actual track is playing?
Otherwise, if the timing still isn't perfect, it might be necessary to create two full-blown player instances and manage them somehow, which seems like a nightmare...

[BobcatNoah]

The timing isn't perfect and I can't think of any way to account for the latency added by seeking. Fading the volume down may work, but I'm not sure how well. I have no way knowing when the track is actually playing after the seek and just adding a few seconds would sound bad on devices that seek really fast.
I don't think crossfade is worth creating two full-blown player instances. It definitely would be a nightmare.

[Chaphasilor]

Hi @BobcatNoah, sorry that I never managed to take a closer look.
I was planning to do that once the initial beta release is done. Is there any particular reason why you closed the PR? :)

[BobcatNoah]

From my testing, I noticed that different devices had different delays for when you call the play method and when it actually starts playing. This meant I can never perfectly sync up the transition between the songs. On my phone, it might sound fine but on a car stereo, there might be a noticeable delay.

[BobcatNoah]

Alternatively, I could try the original method of having two separate players in which Finamp would alternate between the two.

[Chaphasilor]

Hmm, okay. Maybe just_audio will get cross-fase support at some point, but that might be a while. The two player approach would be the best solution for cross-fading, but I don't think it would play nicely with the queue and the player itself.
But you're welcome to give it a try, if you feel like it!

[BobcatNoah]

I didn't even consider the queue being a problem. I guess I'll have to put this on hold until just_audio add crossfade.