ios - AudioKit iOS : how can an input node be dynamically connected to mixer in active chain?

Question

输入节点如何动态连接到 AudioKit iOS 事件链中的混音器？

环境:AudioKit 4.3、Swift 4.1、Xcode 9.4.1、iOS 11.4。

问题

我正在构建一个应用程序，其中包含由一系列 AKNode 对象组成的动态模块。这些模块根据请求动态连接到正在运行的 AudioKit 引擎的专用 AKMixer 节点或从中分离。这很好用，除非尝试连接任何包含输入节点(例如 AKMicrophone 或 AKStereoInput)的模块，这会导致崩溃:

2018-06-14 10:13:33.696384-0700 MyApp[3440:2578936] [mcmx] 338: input bus 0 sample rate is 0 2018-06-14 10:13:33.696749-0700 MyApp[3440:2578936] [avae] AVAEInternal.h:103:_AVAE_CheckNoErr: [AVAudioEngineGraph.mm:3632:UpdateGraphAfterReconfig: (AUGraphParser::InitializeActiveNodesInOutputChain(ThisGraph, kOutputChainFullTraversal, *conn.srcNode, isChainActive)): error -10875 2018-06-14 10:13:33.700474-0700 DynamicMic[3440:2578936] *** Terminating app due to uncaught exception 'com.apple.coreaudio.avfaudio', reason: 'error -10875'

或者，调用 AudioKit.stop()，然后执行有问题的连接，然后调用 AudioKit.start() 无法启动 AudioKit，但它避免了崩溃:

AKMicrophone.swift:init():45:Mixer inputs 8 2018-06-14 10:16:09.532277-0700 MyApp[3443:2580588] [mcmx] 338: input bus 0 sample rate is 0 2018-06-14 10:16:09.532603-0700 MyApp[3443:2580588] [avae] AVAEInternal.h:103:_AVAE_CheckNoErr: [AVAudioEngineGraph.mm:1265:Initialize: (err = AUGraphParser::InitializeActiveNodesInOutputChain(ThisGraph, kOutputChainOptimizedTraversal, *GetOutputNode(), isOutputChainActive)): error -10875 2018-06-14 10:16:09.532654-0700 MyApp[3443:2580588] [avae] AVAudioEngine.mm:149:-[AVAudioEngine prepare]: Engine@0x1c0008010: could not initialize, error = -10875 2018-06-14 10:16:09.651495-0700 MyApp[3443:2580588] [mcmx] 338: input bus 0 sample rate is 0 2018-06-14 10:16:09.651549-0700 MyApp[3443:2580588] [avae] AVAEInternal.h:103:_AVAE_CheckNoErr: [AVAudioEngineGraph.mm:1265:Initialize: (err = AUGraphParser::InitializeActiveNodesInOutputChain(ThisGraph, kOutputChainOptimizedTraversal, *GetOutputNode(), isOutputChainActive)): error -10875

唯一可行的方法是以静态方式制作整个音频节点图，包括 AKMicrophone 节点，设置输出节点，然后仅启动 AudioKit 一次。然而，这种方法无法满足我的应用程序所需的动态音频节点图的要求。

代码

这是托管 AudioKit 类的精简版。理想情况下，在 AppDelegate didFinishLaunchingWithOptions 方法等入口点调用 AudioEngine.start()。

import Foundation
import AudioKit

class AudioEngine {

    private static var _mainMixer: AKMixer = AKMixer()

    // Connected main mixer input nodes.
    private static var _mainMixerNodes = [AKNode]()

    private static var _isInited = false
    private static var _isStarted = false

    static func start() {
        if !_isInited {
            // Clean tempFiles !
            AKAudioFile.cleanTempDirectory()

            // Session settings
            AKSettings.bufferLength = .medium

            do {
                try AKSettings.setSession(category: .playAndRecord, with: .allowBluetoothA2DP)
            } catch {
                AKLog("Could not set session category.")
            }

            AKSettings.defaultToSpeaker = true
            _isInited = true
        }
        if !_isStarted {
            AudioKit.output = _mainMixer
            print("AudioEngine start: just set output to global mixer")
            do {
                try AudioKit.start()
                AKLog("AudioEngine: AudioKit started")
                _isStarted = true
            } catch {
                AKLog("AudioEngine: AudioKit could not start")
            }
        }
    }

    static func stop() {
        if _isStarted {
            AudioKit.output = nil
            do {
                try AudioKit.stop()
                AKLog("AudioEngine: AudioKit stopped")
                _isStarted = false
            } catch {
                AKLog("AudioEngine: AudioKit could not stop")
            }
        }
    }

    static func connect(_ node: AKNode) {
        if !_mainMixerNodes.contains(node) {
            _mainMixer.connect(input: node)
            _mainMixerNodes.append(node)
        }
    }

    static func disconnect(_ node: AKNode) {
        if let nodeIndex = _mainMixerNodes.index(of: node) {
            node.detach()
            _mainMixerNodes.remove(at: nodeIndex)
        }
    }

}

稍后在应用程序流程中，将打开一个自定义 View ，该 View 通过输入节点 (AKMicrophone) 使用麦克风。这就是问题发生的地方。这是一个精简版:

import UIKit

import AudioKit

class MicViewController: UIViewController {

    let mic = AKMicrophone()

    override func viewDidLoad() {
        super.viewDidLoad()

        // Approach 1: Causes a crash.
        AudioEngine.connect(mic)

        // Approach 2: Stop engine, connect, start engine again. Does not work.
        // AudioEngine.stop()
        // AudioEngine.connect(mic)
        // AudioEngine.start()
    }

}

Answer 1

在 disconnect 中，detach 将从底层 AVAudioEngine 中分离节点。 AKMicrophone 的底层节点是 AVAudioEngine 的属性，因此最好断开它。

let disconnect = node is AKMicrophone ? disconnectOutput : detach
node.disconnect()

但静音更容易。

mic.volume = 0