swift iOS 中的實時音高變換

Question

我想實現一個 iOS 應用程序（快速），它可以改變手機麥克風輸入的音高，並在用戶以最小延遲（最多幾毫秒）說話時通過揚聲器播放修改后的語音。 到目前為止，我有以下代碼：

import UIKit
import AVFoundation

class ViewController: UIViewController {
    
    var player : AVAudioPlayerNode!
    var timePitch : AVAudioUnitTimePitch!
    var engine : AVAudioEngine!
    
    override func viewDidLoad() {
        super.viewDidLoad()
        self.timePitch = AVAudioUnitTimePitch()
        self.player = AVAudioPlayerNode()
        self.engine = AVAudioEngine()

        timePitch.pitch = -500
        timePitch.rate = 1.0
        
        engine.inputNode.installTap(onBus: 0, bufferSize: 4410, format: engine.inputNode.outputFormat(forBus: 0), block: {
            (buffer: AVAudioPCMBuffer, time: AVAudioTime) in
            self.engine.attach(self.player)
            self.engine.attach(self.timePitch)
            self.engine.connect(self.player, to: self.timePitch, format: buffer.format)
            self.engine.connect(self.timePitch, to: self.engine.mainMixerNode, format: buffer.format)
            self.player.scheduleBuffer(buffer, at: nil, options: AVAudioPlayerNodeBufferOptions.loops, completionHandler: nil)
            self.player.play()
        })
        engine.prepare()
        do {
            try engine.start()
        } catch _ {
            print("Failed to start engine!")
        }
    }
}

但是，一旦我運行該應用程序，我就會收到以下錯誤：

2020-07-27 01:06:03.972753+0430 Pitch Shifter[37745:5251379] [plugin] AddInstanceForFactory: No factory registered for id <CFUUID 0x6000031f40e0> F8BB1C28-BAE8-11D6-9C31-00039315CD46
2020-07-27 01:06:04.152148+0430 Pitch Shifter[37745:5251392] *** Terminating app due to uncaught exception 'com.apple.coreaudio.avfaudio', reason: 'player started when in a disconnected state'
*** First throw call stack:
(
    0   CoreFoundation                      0x00007fff23c7127e __exceptionPreprocess + 350
    1   libobjc.A.dylib                     0x00007fff513fbb20 objc_exception_throw + 48
    2   CoreFoundation                      0x00007fff23c70ff8 +[NSException raise:format:arguments:] + 88
    3   AVFAudio                            0x00007fff20a7ff67 _Z19AVAE_RaiseExceptionP8NSStringz + 156
    4   AVFAudio                            0x00007fff20b13c57 _ZN21AVAudioPlayerNodeImpl9StartImplEP11AVAudioTime + 453
    5   AVFAudio                            0x00007fff20b116cc -[AVAudioPlayerNode play] + 60
    6   Pitch Shifter                       0x000000010c06a25d $s13Pitch_Shifter14ViewControllerC11viewDidLoadyyFySo16AVAudioPCMBufferC_So0H4TimeCtcfU_ + 3005
    7   Pitch Shifter                       0x000000010c06a32f $sSo16AVAudioPCMBufferCSo0A4TimeCIeggg_AbDIeyByy_TR + 95
    8   AVFAudio                            0x00007fff20aaee1b _ZN14AVAudioNodeTap10TapMessage25RealtimeMessenger_PerformEv + 1325
    9   AVFAudio                            0x00007fff20b21e4b _ZN17RealtimeMessenger23_PerformPendingMessagesEv + 59
    10  AVFAudio                            0x00007fff20b21df2 ___ZN17RealtimeMessengerC2EN10applesauce8dispatch2v15queueE_block_invoke + 97
    11  libdispatch.dylib                   0x000000010c397d48 _dispatch_client_callout + 8
    12  libdispatch.dylib                   0x000000010c39a6ba _dispatch_continuation_pop + 552
    13  libdispatch.dylib                   0x000000010c3ada0f _dispatch_source_invoke + 2205
    14  libdispatch.dylib                   0x000000010c39e40e _dispatch_lane_serial_drain + 307
    15  libdispatch.dylib                   0x000000010c39f1b5 _dispatch_lane_invoke + 476
    16  libdispatch.dylib                   0x000000010c3a928c _dispatch_root_queue_drain + 351
    17  libdispatch.dylib                   0x000000010c3a907f _dispatch_worker_thread + 278
    18  libsystem_pthread.dylib             0x00007fff52466109 _pthread_start + 148
    19  libsystem_pthread.dylib             0x00007fff52461b8b thread_start + 15
)
libc++abi.dylib: terminating with uncaught exception of type NSException

任何解決此問題的幫助表示贊賞。

編輯：

我認為問題在於installTap回調 function 從未被調用，因此鏈被破壞。

如果我使用 AVFoundation 的時間效果來處理實時麥克風輸入的方法是正確的，如何解決這個錯誤？

或者，如果我的方法方向錯誤，如何以最小延遲（最多延遲幾毫秒）實時更改設備麥克風的輸入音高？

Answer 1

我找不到上述問題的正確答案，如果有人能回答我將不勝感激，但現在我發現AudioKit是一個很棒的聲音處理庫，並且可以完美地完成工作。

如果將來有人需要，這是我項目源代碼的鏈接。

import UIKit
import AudioKit
import AudioKitUI

class ViewController: UIViewController {

    @IBOutlet weak var slider: UISlider!
    @IBOutlet weak var label: UILabel!
    @IBOutlet var audioInputPlot: AKNodeOutputPlot!
    
    var micBooster: AKBooster?
    var pitchShifter: AKPitchShifter?
    var tracker: AKFrequencyTracker!
    let mic = AKMicrophone()
    
    override func viewDidLoad() {
        super.viewDidLoad()
        AKSettings.sampleRate = AudioKit.engine.inputNode.inputFormat(forBus: 0).sampleRate
        
        let micMixer = AKMixer(mic)
        tracker = AKFrequencyTracker.init(mic)
        micBooster = AKBooster(micMixer)

        pitchShifter = AKPitchShifter(micBooster, shift: 0)

        micBooster!.gain = 5

        AudioKit.output = pitchShifter
        
        do{
            try AudioKit.start()
        } catch {
            print("error occured")
        }
    }
}