从麦克风播放音频

Question

目标：将音频/视频从一台设备流式传输到另一台设备。

问题：我设法获得了音频和视频，但音频无法在另一边播放。

---

详情：

我创建了一个应用程序，可以通过网络将 A/V 数据从一台设备传输到另一台设备。为了不涉及太多细节，我将向您展示我卡在哪里。我设法听取了输出委托，在那里我提取了音频信息，将其转换为数据并将其传递给我创建的委托。

func captureOutput(_ captureOutput: AVCaptureOutput!, didOutputSampleBuffer sampleBuffer: CMSampleBuffer!, from connection: AVCaptureConnection!) {
    // VIDEO | code excluded for simplicity of this question as this part works

    // AUDIO | only deliver the frames if you are allowed to
    if self.produceAudioFrames == true {
        // process the audio buffer
        let _audioFrame = self.audioFromSampleBuffer(sampleBuffer)
        // process in async
        DispatchQueue.main.async {
            // pass the audio frame to the delegate
            self.delegate?.audioFrame(data: _audioFrame)
        }
    }
}

转换 SampleBuffer 的辅助函数（不是我的代码，找不到源代码。我知道在 SO 上找到它）：

func audioFromSampleBuffer(_ sampleBuffer: CMSampleBuffer) -> Data {

    var audioBufferList = AudioBufferList()
    var data = Data()
    var blockBuffer : CMBlockBuffer?

    CMSampleBufferGetAudioBufferListWithRetainedBlockBuffer(sampleBuffer, 
                                                            nil,
                                                            &audioBufferList, 
                                                            MemoryLayout<AudioBufferList>.size, 
                                                            nil, 
                                                            nil, 
                                                            0, 
                                                            &blockBuffer)

    let buffers = UnsafeBufferPointer<AudioBuffer>(start: &audioBufferList.mBuffers, 
                                                   count: Int(audioBufferList.mNumberBuffers))
    for audioBuffer in buffers {
        let frame = audioBuffer.mData?.assumingMemoryBound(to: UInt8.self)
        data.append(frame!, count: Int(audioBuffer.mDataByteSize))
    }
    // dev
    //print("audio buffer count: \(buffers.count)") | this returns 2048
    // give the raw data back to the caller
    return data
}

注意：在通过网络发送之前，我将 helper func 返回的数据转换为：let payload = Array(data)

那是主人的一面。

在客户端，我以[UInt8] 的形式接收有效负载，这就是我卡住的地方。我尝试了多种方法，但都没有奏效。

func processIncomingAudioPayloadFromFrame(_ ID: String, _ _Data: [UInt8]) {
    let readableData = Data(bytes: _Data) // back from array to the data before we sent it over the network.
    print(readableData.count) // still 2048 even after recieving from network, So I am guessing data is still intact

    let x = self.bytesToAudioBuffer(_Data) // option two convert into a AVAudioPCMBuffer
    print(x) // prints | <AVAudioPCMBuffer@0x600000201e80: 2048/2048 bytes> | I am guessing it works

    // option one | play using AVAudioPlayer
    do {
        let player = try AVAudioPlayer(data: readableData)
        try AVAudioSession.sharedInstance().setCategory(AVAudioSessionCategoryPlayback)
        try AVAudioSession.sharedInstance().setActive(true)
        player.prepareToPlay()
        player.play()
        print(player.volume) // doing this to see if this is reached
    }catch{
        print(error) // gets error | Error Domain=NSOSStatusErrorDomain Code=1954115647 "(null)"
    }
}

这是将[UInt8] 转换为AVAudioPCMBuffer 的辅助函数：

func bytesToAudioBuffer(_ buf: [UInt8]) -> AVAudioPCMBuffer {
    // format assumption! make this part of your protocol?
    let fmt = AVAudioFormat(commonFormat: .pcmFormatFloat32, sampleRate: 44100, 
                            channels: 1, interleaved: true)
    let frameLength = UInt32(buf.count) / fmt.streamDescription.pointee.mBytesPerFrame

    let audioBuffer = AVAudioPCMBuffer(pcmFormat: fmt, frameCapacity: frameLength)
    audioBuffer.frameLength = frameLength

    let dstLeft = audioBuffer.floatChannelData![0]
    // for stereo
    // let dstRight = audioBuffer.floatChannelData![1]

    buf.withUnsafeBufferPointer {
        let src = UnsafeRawPointer($0.baseAddress!).
            bindMemory(to: Float.self, capacity: Int(frameLength))
        dstLeft.initialize(from: src, count: Int(frameLength))
    }
    return audioBuffer
}

问题：

1. 是否可以直接从[UInt8] 播放？
2. 如何使用 AudioEngine 播放 AVAudioPCMBuffer 负载？ 有可能吗？
3. 如何在客户端播放音频。

脚注：代码中的 cmets 应该会给你一些我希望的输出提示。此外，我不想保存到文件或任何相关文件，因为我只想放大麦克风以进行实时收听，我对保存数据没有兴趣。

Answer 1

我使用相同的代码在运营商通话中播放音频文件。

请尝试让我知道结果：

目标代码：

NSString *soundFilePath = [[NSBundle mainBundle] 
pathForResource:self.bgAudioFileName ofType: @"mp3"];    

NSURL *fileURL = [[NSURL alloc] initFileURLWithPath:soundFilePath ];

myAudioPlayer = [[AVAudioPlayer alloc] initWithContentsOfURL:fileURL 
error:nil];

myAudioPlayer.numberOfLoops = -1;

NSError *sessionError = nil;

// Change the default output audio route
AVAudioSession *audioSession = [AVAudioSession sharedInstance];

 // get your audio session somehow
[audioSession setCategory:AVAudioSessionCategoryMultiRoute 
 error:&sessionError];

BOOL success= [audioSession         
overrideOutputAudioPort:AVAudioSessionPortOverrideNone 
error:&sessionError];

 [audioSession setActive:YES error:&sessionError];
 if(!success)
 {
     NSLog(@"error doing outputaudioportoverride - %@", [sessionError    
     localizedDescription]);
}
 [myAudioPlayer setVolume:1.0f];
 [myAudioPlayer play];

斯威夫特版本：

 var soundFilePath: String? = Bundle.main.path(forResource: 
 bgAudioFileName, ofType: "mp3")
 var fileURL = URL(fileURLWithPath: soundFilePath ?? "")
 myAudioPlayer = try? AVAudioPlayer(contentsOf: fileURL)
 myAudioPlayer.numberOfLoops = -1
 var sessionError: Error? = nil
// Change the default output audio route
 var audioSession = AVAudioSession.sharedInstance()
 // get your audio session somehow
 try? audioSession.setCategory(AVAudioSessionCategoryMultiRoute)
 var success: Bool? = try? 
 audioSession.overrideOutputAudioPort(AVAudioSessionPortOverrideNone 
 as? AVAudioSessionPortOverride ?? AVAudioSessionPortOverride())
 try? audioSession.setActive(true)
 if !(success ?? false) {
   print("error doing outputaudioportoverride - \
      (sessionError?.localizedDescription)")
   }
  myAudioPlayer.volume = 1.0
  myAudioPlayer.play()