AVAudioEngine inputNode installTap crash when restarting recording

Question

I am implementing Speech Recognition in my app. When I first present the view controller with the speech recognition logic, everything works fine. However, when I try present the view controller again, I get the following crash:

ERROR:    [0x190bf000] >avae> AVAudioNode.mm:568: CreateRecordingTap: required condition is false: IsFormatSampleRateAndChannelCountValid(format)
*** Terminating app due to uncaught exception 'com.apple.coreaudio.avfaudio', reason: 'required condition is false: IsFormatSampleRateAndChannelCountValid(format)'

Here is the code used for starting and stopping recording:

@available(iOS 10.0, *)
extension DictationViewController {

fileprivate func startRecording() throws {
    guard let recognizer = speechRecognizer else {
        debugLog(className, message: "Not supported for the device's locale")
        return
    }

    guard recognizer.isAvailable else {
        debugLog(className, message: "Recognizer is not available right now")
        return
    }

    mostRecentlyProcessedSegmentDuration = 0
    guard let node = audioEngine.inputNode else {
        debugLog(className, message: "Could not get an input node")
        return
    }

    let recordingFormat = node.outputFormat(forBus: 0)
    node.installTap(onBus: 0, bufferSize: 1024, format: recordingFormat) { [weak self] (buffer, _) in
        self?.request.append(buffer)
    }

    audioEngine.prepare()
    try audioEngine.start()

    recognitionTask = recognizer.recognitionTask(with: request, resultHandler: {/***/})
}

fileprivate func stopRecording() {
    audioEngine.stop()
    audioEngine.inputNode?.removeTap(onBus: 0)
    request.endAudio()
    recognitionTask?.cancel()
}

}

startRecording() is called in viewDidLoad once we have requested authorization. stopRecording() is called when the view controller is dismissed.

Please assist. I'm struggling to find a solution to this crash

Answer 1

First, a small issue. When tapping the device's microphone, you'll want to use the format of the input bus:

let recordingFormat = node.inputFormat(forBus: 0)

Second, after some digging it seems like this crash most commonly stems from your application's shared AVAudioSession category settings. Make sure you have your audio session configured like so if you're going to be performing live microphone audio processing:

private func configureAudioSession() {
    do {
        try AVAudioSession.sharedInstance().setCategory(AVAudioSessionCategoryPlayAndRecord, with: .mixWithOthers)
        try AVAudioSession.sharedInstance().setActive(true)
    } catch { }
}

Answer 2

There are two possible ways to solve this problem.

1. Check inputFormat.channelCount. It may be throwing the error because the mic is in use in another application or somewhere else you yours.

if(inputNode.inputFormat(forBus: 0).channelCount == 0){
    NSLog("Not enough available inputs!")
    return
}

2. Try to reset the audioEngine.

audioEngine.reset()

Answer 3

I was getting the required condition is false: IsFormatSampleRateAndChannelCountValid(format) crash when attempting to use speech recognition while taking a phone call, which caused the sample rate to equal zero. My solution was to create the below audioInputIsBusy() function and call it before try audioSession.setCategory(.record, mode: .measurement, options: .duckOthers) That prevented the crash and I displayed a message that the "speech recognition is unavailable" and then reset the audioEngine with audioEngine = AVAudioEngine().

func audioInputIsBusy(recordingFormat: AVAudioFormat) -> Bool {
    guard recordingFormat.sampleRate == 0 || recordingFormat.channelCount == 0 else {
        return false
    }

    return true
}

ps: let recordingFormat = audioEngine.inputNode.outputFormat(forBus: 0)

Answer 4

You can replace this code:

let recordingFormat = node.outputFormat(forBus: 0)

with the following:

let recordingFormat = AVAudioFormat(standardFormatWithSampleRate: 44100, channels: 1)

This code fixed the problem.

Answer 5

I had to call the removeTap() before installTap in order to make it work. None of the solutions above worked for me.

//Remove tap first.
inputNode.removeTap(onBus: 0)

// Configure the microphone input.
let recordingFormat = inputNode.inputFormat(forBus: 0)            
inputNode.installTap(onBus: 0, bufferSize: 1024, format: recordingFormat) { (buffer: AVAudioPCMBuffer, when: AVAudioTime) in
            //process buffer...
        }

Answer 6

class AudioRecordProvider {
  
    var audioEngine = AVAudioEngine()
    let mixerNode = AVAudioMixerNode()

    
    func startListening() throws {
        guard !audioEngine.isRunning else { return }
        let audioSession = AVAudioSession.sharedInstance()
        
        try audioSession.setCategory(.playAndRecord)
        
        audioSession.requestRecordPermission { [weak self] success in
            guard success, let self = self else { return }
            try? self.audioEngine.start()
        }
    }
    
    func stopListening() {
        if audioEngine.isRunning {
            audioEngine.stop()
        }
    }


    
    func configureAudioEngine() {
        self.audioEngine = AVAudioEngine()
        let inputFormat = audioEngine.inputNode.inputFormat(forBus: 0)
        
        let outputFormat = AVAudioFormat(standardFormatWithSampleRate: 48000, channels: 1)
        
        audioEngine.attach(mixerNode)

        audioEngine.connect(audioEngine.inputNode, to: mixerNode, format: inputFormat)
        audioEngine.connect(mixerNode, to: audioEngine.outputNode, format: outputFormat)
            
    }
}

This Answer worked for me. It's the usage example. Lifecycle: configureAudioEngine -> startListening -> stopListening. Every call of configureAudioEngine reinit AVAudioEngine and it works.

Answer 7

try this, before start running each time:

audioEngine = AVAudioEngine()