将多个 AVAudioMixerNode 连接到 AVAudioEngine

Question

当我尝试将两个

AVAudioMixerNodes

连接到

AVAudioEngine

的麦克风输入时，出现崩溃。 我在网上找不到如何管理两个或多个节点到同一输入的文档。

处理多个节点监听麦克风的情况的正确方法是什么？

我在后台线程上调用这三个方法：

    private func setupSession() {
        let session = AVAudioSession.sharedInstance()
        do {
            try session.setCategory(.playAndRecord, options: [.mixWithOthers])
            if session.isInputGainSettable {
                try session.setInputGain(0.2)
            }
            try session.setActive(true, options: .notifyOthersOnDeactivation)
        } catch let error as NSError {
            LoggerManager.shared.error(error: error, message: "Error while setting up AVAudioSession Category/Active status")
        }
    }

    private func setupMixerNodes() {
        analyzerNode = AVAudioMixerNode()
        analyzerNode.volume = 0

        volumeNode = AVAudioMixerNode()
        volumeNode.volume = 0

        engine.attach(analyzerNode)
        engine.attach(volumeNode)
    }

    private func makeConnections() {
        /* input microphone */
        let inputNode = engine.inputNode

        let inputFormat = inputNode.outputFormat(forBus: 0)
        let analyzerConnectionPoint = AVAudioConnectionPoint(node: analyzerNode, bus: 0)
        let volumeConnectionPoint = AVAudioConnectionPoint(node: volumeNode, bus: 0)
        engine.connect(inputNode, to: [analyzerConnectionPoint, volumeConnectionPoint], fromBus: 0, format: inputFormat)

        let mainMixerNode = engine.mainMixerNode
        let mixerFormat = AVAudioFormat(commonFormat: .pcmFormatFloat32, sampleRate: inputFormat.sampleRate, channels: 1, interleaved: false)

        engine.connect(analyzerNode, to: mainMixerNode, fromBus: 0, toBus: 0, format: mixerFormat)
        engine.connect(volumeNode, to: mainMixerNode, fromBus: 0, toBus: 1, format: mixerFormat)
    }

我遇到了这个崩溃：

 AURemoteIO.cpp:1128  failed: -10851 (enable 1, outf< 2 ch,      0 Hz, Float32, deinterleaved> inf< 2 ch,      0 Hz, Float32, deinterleaved>)
2022-03-08 12:59:57.950612-0500 SnoreLabo[2914:456147] [avae]            AVAEInternal.h:76    required condition is false: [AVAudioEngineGraph.mm:2401:ConnectMultipleOutputs: (IsFormatSampleRateAndChannelCountValid(format))]
2022-03-08 12:59:58.030789-0500 SnoreLabo[2914:456147] *** Terminating app due to uncaught exception 'com.apple.coreaudio.avfaudio', reason: 'required condition is false: IsFormatSampleRateAndChannelCountValid(format)'
*** First throw call stack:
(0x18273ed3c 0x199aa36a8 0x1828085bc 0x1ddf44eac 0x1ddf9b020 0x1de01bfa0 0x1de018328 0x104d4db1c 0x104d4e1f8 0x104ed4f6c 0x104bcdbe8 0x10dc00718 0x10dc01f94 0x10dc13edc 0x10dc146fc 0x1dcc4ae48 0x1dcc4a9f0)
libc++abi: terminating with uncaught exception of type NSException
dyld4 config: DYLD_LIBRARY_PATH=/usr/lib/system/introspection DYLD_INSERT_LIBRARIES=/Developer/usr/lib/libBacktraceRecording.dylib:/Developer/usr/lib/libMainThreadChecker.dylib:/Developer/Library/PrivateFrameworks/DTDDISupport.framework/libViewDebuggerSupport.dylib
*** Terminating app due to uncaught exception 'com.apple.coreaudio.avfaudio', reason: 'required condition is false: IsFormatSampleRateAndChannelCountValid(format)'
terminating with uncaught exception of type NSException

编辑

我最终使用了这个：

print("Current category: \(AVAudioSession.sharedInstance().category)")
engine.connect(inputNode, to: [analyzerConnectionPoint, volumeConnectionPoint], fromBus: 0, format: inputFormat)

但是我仍然时不时地遇到同样的崩溃...并且当崩溃时类别被正确设置为

.playAndRecord

，所以这不是问题...

Answer 1

文档指出连接可以是一对一、一对多，但绝不能是多对一。

如果要将输出连接到单个输入，则需要使用 AVAudioMixerNode。这就是混音器的用途 - 它将多个信号流混合（组合）为单个流。