Audiokit crashes when changing AKPlayer file - swift

Question

I have recently done the migration from AudioKit 3.7 to 4.2 (using Cocoapods), needed for XCode 9.3. I followed the migration guide and changed AKAudioPlayer to AKPlayer.
The issue
When AKPlayer plays an audio file, AudioKit is crashing with this error:
2018-04-17 09:32:43.042658+0200 hearfit[3509:2521326] [avae] AVAEInternal.h:103:_AVAE_CheckNoErr: [AVAudioEngineGraph.mm:3632:UpdateGraphAfterReconfig: (AUGraphParser::InitializeActiveNodesInOutputChain(ThisGraph, kOutputChainFullTraversal, *conn.srcNode, isChainActive)): error -10875
2018-04-17 09:32:43.049372+0200 hearfit[3509:2521326] *** Terminating app due to uncaught exception 'com.apple.coreaudio.avfaudio', reason: 'error -10875'
*** First throw call stack:
(0x1847d6d8c 0x1839905ec 0x1847d6bf8 0x18a0ff1a0 0x18a11bf58 0x18a12aab0 0x18a128cdc 0x18a1a1738 0x18a1a160c 0x10519192c 0x10519d2f4 0x10519d64c 0x10503afdc 0x10507c4a0 0x10507c01c 0x104f6d9cc 0x1852233d4 0x18477faa8 0x18477f76c 0x18477f010 0x18477cb60 0x18469cda8 0x18667f020 0x18e67d78c 0x10504dfd4 0x18412dfc0)
libc++abi.dylib: terminating with uncaught exception of type NSException
Sometimes it happens on the first play, and sometimes the first play is done correctly, but not the second one.
Everything was working great before the migration. I also tried to keep AKAudioPlayer: sounds are played correctly but AKFrequencyTracker does not work anymore.
Context
This is my setup:
Quick explanation:
AKPlayer 1 plays short audio files (between 1 and 5 seconds)
AKFrequencyTracker is used to display a plot
AKPlayer 2 plays background sound (volume must be configurable)
AKWhiteNoise allows to do some manual volume measurements (using AKMixer 2 volume property)
Use case example
The user starts an exercise. A sound is played continuously (with looping) using AKPlayer 2 and the user listens a word (played with AKPlayer 1), the plot is displayed. Next, several words are displayed on screen and the user must pick the right one. And a new word is listened... and so on.
So I have to change dynamically the played file of AKPlayer 1. All the code is written in a dedicated class, a singleton. All the nodes are setup in the init() function.
// singleton
static let main = AudioPlayer()
private init() {
let silenceUrl = Bundle.main.url(forResource: "silence", withExtension: "m4a", subdirectory: "audio")
self.silenceFile = silenceUrl!
self.mainPlayer = AKPlayer(url: self.silenceFile)!
self.mainPlayer.volume = 1.0
self.freqTracker = AKFrequencyTracker(self.mainPlayer, hopSize: 256, peakCount: 10)
let noiseUrl = Bundle.main.url(forResource: "cocktail-party", withExtension: "m4a", subdirectory: "audio")
self.noiseFile = noiseUrl!
self.noisePlayer = AKPlayer(url: self.noiseFile)!
self.noisePlayer.volume = 1.0
self.noisePlayer.isLooping = true
let mixer = AKMixer(self.freqTracker, self.noisePlayer)
self.whiteNoise = AKWhiteNoise(amplitude: 1.0)
self.whiteNoiseMixer = AKMixer(self.whiteNoise)
self.whiteNoiseMixer.volume = 0
self.mixer = AKMixer(mixer, self.whiteNoiseMixer)
AudioKit.output = self.mixer
do {
try AudioKit.start()
} catch (let error) {
print(error)
}
// stop directly the white noise mixer
self.whiteNoise.stop()
self.whiteNoiseMixer.volume = self.whiteNoiseVolume
self.mainPlayer.completionHandler = {
DispatchQueue.main.async {
if let timer = self.timer {
timer.invalidate()
self.timer = nil
}
if let completion = self.completionHandler {
Timer.scheduledTimer(withTimeInterval: 0.5, repeats: false, block: { (_) in
completion()
self.completionHandler = nil
})
}
}
}
}
To change the AKPlayer 1 audio file, I use this function, on the same class:
func play(fileUrl: URL, tracker: #escaping TrackerCallback, completion: (() -> Void)?) throws {
self.completionHandler = completion
let file = try AKAudioFile(forReading: fileUrl)
self.mainPlayer.load(audioFile: file)
self.mainPlayer.preroll()
self.timer = Timer.scheduledTimer(withTimeInterval: self.trackerRefreshRate, repeats: true) { (timer) in
tracker(self.freqTracker.frequency, self.freqTracker.amplitude)
}
self.mainPlayer.play()
}
Thank you.

Answer 1

I'm not sure what you are replacing into the player, but if the format of the file is different from what you had before, channels, samplerate, etc -- you should create a new AKPlayer instance rather than load into the same one. If your files are all the same format then it should work ok.
That said, I haven't seen the crash you show.
Another thing that is dangerous in your code is force unwrapping those optionals - you should guard against things being nil. AKPlayer actually uses AVAudioFile, no need for AKAudioFile.
guard let akfile = try? AVAudioFile(forReading: url) else { return }
if akfile.channelCount != player?.audioFile?.processingFormat.channelCount ||
akfile.sampleRate != player?.audioFile?.processingFormat.sampleRate {
AKLog("Need to create new player as formats have changed.")
}