AVAudioEngine 实现耳返功能

很简单，应该可以看懂吧

private var engine: AVAudioEngine?

extension PithyisCool {

    private func startEarReturn() {

        engine = AVAudioEngine()

        guard let engine = engine else { return }

        let playNode = AVAudioPlayerNode()

        engine.attach(playNode)

        let input = engine.inputNode

        let output = engine.outputNode

        engine.connect(input,to: output,format: input.inputFormat(forBus: 0))

        engine.prepare()

        do {

            try engine.start()

        } catch {

        }

    }

    private func stopEarReturn() {

        engine?.stop()

        engine?.inputNode.removeTap(onBus: 0)

        engine = nil

    }

}