我正在开发一个 iOS 应用程序，它由 2 个主要模块组成:一个基于 Core Audio 的音频分析模块，以及一个使用 AudioKit 的输出模块。

这是音频输入类:

import AVFoundation

typealias AudioInputCallback = (
    _ timeStamp: Double,
    _ numberOfFrames: Int,
    _ samples: [Float]
    ) -> Void

/// Sets up an audio input session and notifies when new buffer data is available.
class AudioInputUtility: NSObject {

    private(set) var audioUnit: AudioUnit!
    var audioSession : AVAudioSession = AVAudioSession.sharedInstance()
    var sampleRate: Float
    var numberOfChannels: Int

    /// When true, performs DC offset rejection on the incoming buffer before invoking the audioInputCallback.
    var shouldPerformDCOffsetRejection: Bool = false

    private let outputBus: UInt32 = 0
    private let inputBus: UInt32 = 1
    private var audioInputCallback: AudioInputCallback!

    /// Instantiate a AudioInput.
    /// - Parameter audioInputCallback: Invoked when audio data is available.
    /// - Parameter sampleRate: The sample rate to set up the audio session with.
    /// - Parameter numberOfChannels: The number of channels to set up the audio session with.

    init(audioInputCallback callback: @escaping AudioInputCallback, sampleRate: Float = 44100.0, numberOfChannels: Int = 1) { // default values if not specified

        self.sampleRate = sampleRate
        self.numberOfChannels = numberOfChannels
        audioInputCallback = callback
    }

    /// Start recording. Prompts for access to microphone if necessary.
    func startRecording() {
        do {

            if self.audioUnit == nil {
                setupAudioSession()
                setupAudioUnit()
            }

            try self.audioSession.setActive(true)
            var osErr: OSStatus = 0


            osErr =  AudioUnitInitialize(self.audioUnit)
            assert(osErr == noErr, "*** AudioUnitInitialize err \(osErr)")
            osErr = AudioOutputUnitStart(self.audioUnit)

            assert(osErr == noErr, "*** AudioOutputUnitStart err \(osErr)")
        } catch {
            print("*** startRecording error: \(error)")
        }
    }

    /// Stop recording.
    func stopRecording() {
        do {
            var osErr: OSStatus = 0

            osErr = AudioOutputUnitStop(self.audioUnit)
            osErr = AudioUnitUninitialize(self.audioUnit)

            assert(osErr == noErr, "*** AudioUnitUninitialize err \(osErr)")

            try self.audioSession.setActive(false)

        } catch {
            print("*** error: \(error)")
        }
    }

    private let recordingCallback: AURenderCallback = { (inRefCon, ioActionFlags, inTimeStamp, inBusNumber, inNumberFrames, ioData) -> OSStatus in

        let audioInput = unsafeBitCast(inRefCon, to: AudioInputUtility.self)
        var osErr: OSStatus = 0

        // We've asked CoreAudio to allocate buffers for us, so just set mData to nil and it will be populated on AudioUnitRender().
        var bufferList = AudioBufferList(
            mNumberBuffers: 1,
            mBuffers: AudioBuffer(
                mNumberChannels: UInt32(audioInput.numberOfChannels),
                mDataByteSize: 4,
                mData: nil))

        osErr = AudioUnitRender(audioInput.audioUnit,
                                ioActionFlags,
                                inTimeStamp,
                                inBusNumber,
                                inNumberFrames,
                                &bufferList)
        assert(osErr == noErr, "*** AudioUnitRender err \(osErr)")


        // Move samples from mData into our native [Float] format.
        var monoSamples = [Float]()
        let ptr = bufferList.mBuffers.mData?.assumingMemoryBound(to: Float.self)
        monoSamples.append(contentsOf: UnsafeBufferPointer(start: ptr, count: Int(inNumberFrames)))

        if audioInput.shouldPerformDCOffsetRejection {
            DCRejectionFilterProcessInPlace(&monoSamples, count: Int(inNumberFrames))
        }

        // Not compatible with Obj-C...
        audioInput.audioInputCallback(inTimeStamp.pointee.mSampleTime / Double(audioInput.sampleRate),
                                      Int(inNumberFrames),
                                      monoSamples)

        return 0
    }

    private func setupAudioSession() {

        if !audioSession.availableCategories.contains(AVAudioSessionCategoryRecord) {
            print("can't record! bailing.")
            return
        }

        do {

            //https://developer.apple.com/reference/avfoundation/avaudiosession/1669963-audio_session_categories
            try audioSession.setCategory(AVAudioSessionCategoryRecord)

            // "Appropriate for applications that wish to minimize the effect of system-supplied signal processing for input and/or output audio signals."
            // NB: This turns off the high-pass filter that CoreAudio normally applies.


            try audioSession.setMode(AVAudioSessionModeMeasurement)

            try audioSession.setPreferredSampleRate(Double(sampleRate))

            // NB: This is considered a 'hint' and more often than not is just ignored.

            // number of seconds to record -> voglio 1024 samples
            try audioSession.setPreferredIOBufferDuration(0.05)

            audioSession.requestRecordPermission { (granted) -> Void in
                if !granted {
                    print("*** record permission denied")
                }
            }
        } catch {
            print("*** audioSession error: \(error)")
        }
    }

    private func setupAudioUnit() {

        var componentDesc:AudioComponentDescription = AudioComponentDescription(
            componentType: OSType(kAudioUnitType_Output),
            componentSubType: OSType(kAudioUnitSubType_RemoteIO), // Always this for iOS.
            componentManufacturer: OSType(kAudioUnitManufacturer_Apple),
            componentFlags: 0,
            componentFlagsMask: 0)

        var osErr: OSStatus = 0

        // Get an audio component matching our description.
        let component: AudioComponent! = AudioComponentFindNext(nil, &componentDesc)
        assert(component != nil, "Couldn't find a default component")

        // Create an instance of the AudioUnit
        var tempAudioUnit: AudioUnit?
        osErr = AudioComponentInstanceNew(component, &tempAudioUnit)
        self.audioUnit = tempAudioUnit

        assert(osErr == noErr, "*** AudioComponentInstanceNew err \(osErr)")

        // Enable I/O for input.
        var one:UInt32 = 1

        osErr = AudioUnitSetProperty(audioUnit,
                                     kAudioOutputUnitProperty_EnableIO,
                                     kAudioUnitScope_Input,
                                     inputBus,
                                     &one,
                                     UInt32(MemoryLayout<UInt32>.size))
        assert(osErr == noErr, "*** AudioUnitSetProperty err \(osErr)")


        osErr = AudioUnitSetProperty(audioUnit,
                                     kAudioOutputUnitProperty_EnableIO,
                                     kAudioUnitScope_Output,
                                     outputBus,
                                     &one,
                                     UInt32(MemoryLayout<UInt32>.size))
        assert(osErr == noErr, "*** AudioUnitSetProperty err \(osErr)")


        // Set format to 32 bit, floating point, linear PCM
        var streamFormatDesc:AudioStreamBasicDescription = AudioStreamBasicDescription(
            mSampleRate:        Double(sampleRate),
            mFormatID:          kAudioFormatLinearPCM,
            mFormatFlags:       kAudioFormatFlagsNativeFloatPacked | kAudioFormatFlagIsNonInterleaved, // floating point data - docs say this is fastest
            mBytesPerPacket:    4,
            mFramesPerPacket:   1,
            mBytesPerFrame:     4,
            mChannelsPerFrame:  UInt32(self.numberOfChannels),
            mBitsPerChannel:    4 * 8,
            mReserved: 0
        )

        // Set format for input and output busses

        osErr = AudioUnitSetProperty(audioUnit,
                                     kAudioUnitProperty_StreamFormat,
                                     kAudioUnitScope_Input, outputBus,
                                     &streamFormatDesc,
                                     UInt32(MemoryLayout<AudioStreamBasicDescription>.size))
        assert(osErr == noErr, "*** AudioUnitSetProperty err \(osErr)")


        osErr = AudioUnitSetProperty(audioUnit,
                                     kAudioUnitProperty_StreamFormat,
                                     kAudioUnitScope_Output,
                                     inputBus,
                                     &streamFormatDesc,
                                     UInt32(MemoryLayout<AudioStreamBasicDescription>.size))
        assert(osErr == noErr, "*** AudioUnitSetProperty err \(osErr)")

        // Set up our callback.
        var inputCallbackStruct = AURenderCallbackStruct(inputProc: recordingCallback, inputProcRefCon: UnsafeMutableRawPointer(Unmanaged.passUnretained(self).toOpaque()))
        osErr = AudioUnitSetProperty(audioUnit,
                                     AudioUnitPropertyID(kAudioOutputUnitProperty_SetInputCallback),
                                     AudioUnitScope(kAudioUnitScope_Global),
                                     inputBus,
                                     &inputCallbackStruct,
                                     UInt32(MemoryLayout<AURenderCallbackStruct>.size))
        assert(osErr == noErr, "*** AudioUnitSetProperty err \(osErr)")

        // Ask CoreAudio to allocate buffers for us on render. (This is true by default but just to be explicit about it...)
        osErr = AudioUnitSetProperty(audioUnit,
                                     AudioUnitPropertyID(kAudioUnitProperty_ShouldAllocateBuffer),
                                     AudioUnitScope(kAudioUnitScope_Output),
                                     inputBus,
                                     &one,
                                     UInt32(MemoryLayout<UInt32>.size))
        assert(osErr == noErr, "*** AudioUnitSetProperty err \(osErr)")
    }
}

private func DCRejectionFilterProcessInPlace(_ audioData: inout [Float], count: Int) {

    let defaultPoleDist: Float = 0.975
    var mX1: Float = 0
    var mY1: Float = 0

    for i in 0..<count {
        let xCurr: Float = audioData[i]
        audioData[i] = audioData[i] - mX1 + (defaultPoleDist * mY1)
        mX1 = xCurr
        mY1 = audioData[i]
    }
}

这是输出类:

private func initPlayer(){
        do{

            /*
            let audioSession : AVAudioSession = AVAudioSession.sharedInstance()
            //try audioSession.setActive(false)
            try audioSession.setCategory(AVAudioSessionCategoryPlayback)
*/            

            // http://audiokit.io/playgrounds/Playback/Reading%20and%20Writing%20Audio%20Files/
            let file = try AKAudioFile(readFileName: self.soundPath,
                                       baseDir: .resources)

            self.player = try AKAudioPlayer(file: file)

            //player options
            self.player!.looping = true




            AKSettings.playbackWhileMuted = true
            try AKSettings.setSession(category: .playback)
AudioKit.output = self.player



        }catch{
            print("Unresolved error \(error)")
        }

    }


public func stopMaskingSound(){

            if(player!.isPlaying){
                self.player!.stop()
            }

            if audioKitIsStarted == true{

                AudioKit.stop()            

                self.audioKitIsStarted = false
            }



        }

如您所见，音频输入和输出由 2 个不同的类管理。

我遇到的问题是，如果我执行以下步骤: 1)初始化播放器和记录 -> 停止它 2) 播放输出 -> 停止 3) 重新初始化播放器

在第 3 步我有这个异常(exception):

[central] 54:   ERROR:    [0x16dfc3000] >avae> AVAudioIONodeImpl.mm:365: _GetHWFormat: required condition is false: hwFormat
*** Terminating app due to uncaught exception 'com.apple.coreaudio.avfaudio', reason: 'required condition is false: hwFormat'

有人知道它与什么有关吗？ AudioKit <-> Core Audio 是否存在任何生命周期问题？

最佳答案

停止和重新启动音频单元可能会出现问题，因为音频进程的某些部分确实在另一个或多个线程中停止。一种可能的解决方法是在停止和重新启动之间允许大约 1 秒的延迟，以允许 RemoteIO 在尝试重新初始化它之前有时间异步停止。

关于iOS 核心音频生命周期 - AVAudioIONodeImpl.mm :365 -required condition is false: hwFormat，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/42282929/