Calling stop() on AVAudioPlayerNode after finished playing causes crash

Question

I have an AVAudioPlayerNode object which sends a callback once it is finished playing. That callback triggers many other functions in the app, one of which sends out a courtesy stop() message. For some reason, calling stop() at the moment the AVAudioPlayerNode finishes causes a crash. In the code here, I have abbreviated it so that the AVAudioPlayerNode just calls stop immediately to demonstrate the effect (rather than including my whole application). You can see clearly that it crashes. I don't understand why. Either a) the node is still playing and stop() stops it or b) it is done playing and stop can be ignored.

My guess is that this is some edge case where it is at the very end of the file buffer, and it is in an ambiguous state where has no more buffers remaining, yet is technically still playing. Perhaps calling stop() tries to flush the remaining buffers and they are empty?

func testAVAudioPlayerNode(){
    let testBundle = Bundle(for: type(of: self))
    let url = URL(fileURLWithPath: testBundle.path(forResource: "19_lyrics_1", ofType: "m4a")!)
    let player = AVAudioPlayerNode()
    let engine = AVAudioEngine()
    let format = engine.mainMixerNode.outputFormat(forBus: 0)
    engine.attach(player)
    engine.connect(player, to: engine.mainMixerNode, format: format)
    let delegate = FakePlayMonitorDelegate()
    do {
        let audioFile = try AVAudioFile(forReading: url)
        let length = audioFile.length
        player.scheduleFile(audioFile, at: nil, completionCallbackType: AVAudioPlayerNodeCompletionCallbackType.dataPlayedBack, completionHandler: {(completionType) in
            print("playing = \(player.isPlaying)")
            player.stop()
        })
        try engine.start()
        let expectation = self.expectation(description: "playback")
        delegate.expectation = expectation
        player.play()
        self.waitForExpectations(timeout: 6.0, handler: nil)
    } catch {

    }
}

This happens to me too, did you even find a solution @dmann200 ? — Brett, Apr 11 '20 at 02:09

Orest · Answer 1 · 2021-03-25T22:04:43.923

5

In my case calling the .stop() method from the Main thread (you can use another) has resolved the issue.

DispatchQueue.main.async {
    player.stop()
}

It can be the deadlock. I have noticed that the completionHandler is invoked from the background queue which is a serial queue, let's call it a "render queue". Seems that the .stop() method is trying to do some work on a "render queue" but at the moment a "render queue" is busy with the completionHandler.

edited Mar 25 '21 at 22:04

answered Jan 21 '21 at 16:16

Orest

51
1
4

My call to `stop()` is already being called in the main thread, I am still seeing these crashes. – JCutting8 Jan 08 '22 at 02:28

score 0 · Answer 2 · answered Apr 03 '23 at 06:48

0

Similarly to Orest, I was able to overcome this issue by placing the .stop() within Task.

Task { 
player.stop()
}

answered Apr 03 '23 at 06:48

dakjac

1
1

Your answer could be improved with additional supporting information. Please [edit] to add further details, such as citations or documentation, so that others can confirm that your answer is correct. You can find more information on how to write good answers [in the help center](/help/how-to-answer). – Community Apr 11 '23 at 05:23

Calling stop() on AVAudioPlayerNode after finished playing causes crash

2 Answers2

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