在硬件上运行时没有可用的audioEngine输入通道

Question

我正在尝试在我的audioEngine的inputNode上设置一个水龙头，以进行语音识别。以下代码可在模拟器中找到，但当我在运行iOS 13.1.2的iPhone X上运行该代码时找不到。

这里是相关代码：

if (audioEngine == nil || (!audioEngine!.isRunning)) {
    print("Setting up audioEngine")
    if audioEngine == nil {
        audioEngine = AVAudioEngine.init()
    }

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

    let recognitionFormat = audioEngine!.inputNode.inputFormat(forBus: 0)
    audioEngine!.inputNode.installTap(onBus: 0, bufferSize: 1024, format: recognitionFormat) {
        (buffer: AVAudioPCMBuffer, when: AVAudioTime) in
        self.recognitionRequest?.append(buffer)
    }
    audioEngine?.prepare()
    try audioEngine?.start()
}

在模拟器中运行时，我没有收到错误，语音识别工作正常。但是，运行我的手机，我得到以下信息：

Setting up audioEngine
[aurioc] AURemoteIO.cpp:1086:Initialize: failed: -10851 (enable 1, outf< 2 ch,      0 Hz, Float32, non-inter> inf< 2 ch,      0 Hz, Float32, non-inter>)
[aurioc] AURemoteIO.cpp:1086:Initialize: failed: -10851 (enable 1, outf< 2 ch,      0 Hz, Float32, non-inter> inf< 2 ch,      0 Hz, Float32, non-inter>)
Not enough available inputs!

如果我在channelCount == 0之后没有返回，则该应用程序将崩溃，并显示：

[avae]            AVAEInternal.h:76    required condition is false: [AVAEGraphNode.mm:823:CreateRecordingTap: (IsFormatSampleRateAndChannelCountValid(format))]
*** Terminating app due to uncaught exception 'com.apple.coreaudio.avfaudio', reason: 'required condition is false: IsFormatSampleRateAndChannelCountValid(format)'

我的音频会话的设置如下：

try audioSession.setCategory(.playAndRecord, options: [.defaultToSpeaker])
try audioSession.setActive(true)

并检查可用输入的结果：

LIST OF INPUTS: [<AVAudioSessionPortDescription: 0x280eac6b0, type = MicrophoneBuiltIn; name = iPhone Microphone; UID = Built-In Microphone; selectedDataSource = Bottom>]

我很困惑。有帮助吗？

Answer 1

我想出了问题。问题与Flutter有关（此应用程序正在使用，但我认为不相关。）事实证明这是相关的。显然FlutterAppDelegate@application方法不在主队列上运行，这是我启动AudioSession的地方。当我像这样启动我的AudioSession时，我的问题就消失了：

DispatchQueue.main.async {
    let audioSession = AVAudioSession.sharedInstance()
    do {
        try audioSession.setCategory(.playAndRecord, mode: .spokenAudio, options: .defaultToSpeaker)
        try audioSession.setActive(true, options: .notifyOthersOnDeactivation)
    } catch {
        print("Failed to setup audio session")
    }
}