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As the title says, I need to route audio data from the phone's microphone out to AirPods or other connected headphones with AVAudioEngine. I've been able to get a version of this working where input is taken from the AirPods mic, but when I set the preferred input source of the AVAudioSession to the built in iPhone mic, I get no output.

Some relevant snippets of my code:

try AVAudioSession.sharedInstance().setCategory(.playAndRecord, options: [.allowBluetooth])
try AVAudioSession.sharedInstance().setMode(.voiceChat)

if let phoneMicIndex = AVAudioSession.sharedInstance().availableInputs?.firstIndex(where: { $0.portType == .builtInMic }) {
    try AVAudioSession.sharedInstance().setPreferredInput(AVAudioSession.sharedInstance().availableInputs?[phoneMicIndex])
}

self.audioEngine.connect(self.audioEngine.inputNode, to: drc, format: self.audioEngine.inputNode.outputFormat(forBus: Config.bus))
self.audioEngine.connect(drc, to: self.audioEngine.mainMixerNode, format: self.audioEngine.outputNode.outputFormat(forBus: Config.bus))

// drc is just an audio unit...

self.audioEngine.inputNode.installTap(onBus: Config.bus, bufferSize: AVAudioFrameCount(Config.bufferSize), format: self.audioEngine.inputNode.inputFormat(forBus: Config.bus), block: { (buffer: AVAudioPCMBuffer, time: AVAudioTime) in
    // I get audio data here, it just isn't played out via the AirPods...
})
tallen11
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  • I've been struggling with this for many hours too. Have you found a solution? – Sam Jul 02 '21 at 02:06
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    @Sam unfortunately not. I ended up writing it all in C using CoreAudio. Not the prettiest thing ever but it was the only thing I could get to work. – tallen11 Jul 02 '21 at 03:51

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