实时音频处理

使用 AVAudioEngine 进行音频处理。 对音频格式进行二次处理，已满足数据处理音频格式要求

import AVFoundation
import Foundation

class MicrophoneAudioStream {
    private var audioEngine: AVAudioEngine!
    var audioInputNode: AVAudioInputNode!
    private var audioFile: AVAudioFile?

    // 定义处理音频缓冲区数据的闭包类型
    typealias AudioBufferHandler = (AVAudioPCMBuffer, AVAudioTime) -> Void
    init() {
        setupAudioEngine()
    }

    private func setupAudioEngine() {
        audioEngine = AVAudioEngine()
        audioInputNode = audioEngine.inputNode
        let audioFormat = audioInputNode.inputFormat(forBus: 0)

        guard let documentsDirectory = FileManager.default.urls(for: .documentDirectory, in: .userDomainMask).first else {
            return
        }
        let audioFileURL = documentsDirectory.appendingPathComponent("audio.wav")

        // 创建AVAudioFile对象
        do {
            audioFile = try AVAudioFile(forWriting: audioFileURL, settings: audioFormat.settings, commonFormat: audioFormat.commonFormat, interleaved: audioFormat.isInterleaved)
        } catch {
            print("Error creating audio file: \(error.localizedDescription)")
        }
    }

    func start() {
        // Start the audio engine
        do {
            try audioEngine.start()
        } catch {
            print("Error starting audio engine: \(error.localizedDescription)")
        }
    }

    // 提供外部方法，接收闭包作为参数
    func startAudioStream(withBufferHandler handler: @escaping AudioBufferHandler) {
        audioInputNode = audioEngine.inputNode

        // 在设置音频格式之前先停止音频引擎
        audioEngine.stop()
        audioInputNode.removeTap(onBus: 0)


        let inputNodeOutputFormat = audioInputNode.outputFormat(forBus: 0)
        let targetFormat = AVAudioFormat(commonFormat: .pcmFormatFloat32, sampleRate: Double(16000), channels: 1, interleaved: false)
        let formatConverter =  AVAudioConverter(from:inputNodeOutputFormat, to: targetFormat!)
        
        
        
        
        audioInputNode.installTap(onBus: 0, bufferSize: 1024, format: inputNodeOutputFormat) { (buffer, time) in
                let pcmBuffer = AVAudioPCMBuffer(pcmFormat: targetFormat!, frameCapacity: AVAudioFrameCount(targetFormat!.sampleRate) / 10)
                var error: NSError? = nil
            
                let inputBlock: AVAudioConverterInputBlock = { inNumPackets, outStatus in
                    outStatus.pointee = AVAudioConverterInputStatus.haveData
                    return buffer
                }
                formatConverter!.convert(to: pcmBuffer!, error: &error, withInputFrom: inputBlock)
             guard let pcmBuffer = pcmBuffer else {return}
             handler(pcmBuffer, time)

        }
        
        // 启动音频引擎
        do {
            audioEngine.prepare()
            try audioEngine.start()
        } catch {
            print("Error starting audio engine: \(error.localizedDescription)")
        }
    }
    

    func stopAudioEngine() {
        audioEngine.stop()
        audioInputNode.removeTap(onBus: 0)
    }

    private func writeAudioBuffer(_ audioBuffer: AVAudioPCMBuffer) {

        // 将音频数据写入文件
        if let audioFile = audioFile {
            do {
                try audioFile.write(from: audioBuffer)
            } catch {
                print("Error writing to audio file: \(error.localizedDescription)")
            }
        }
    }
}