1. .driver 插件

#include 头文件

static AudioServerPlugInDriverInterface gAudioServerPlugInDriverInterface = 静态函数struct， 返回一系列回调的函数指针

//开始io，代表有对象链接进来了，如果是第一个启动引擎， 创建circle buffer

static OSStatus xxx_StartIO(AudioServerPlugInDriverRef inDriver, AudioObjectID inDeviceObjectID, UInt32 inClientID)

//如果是最后一个的话，关闭引擎，销毁circle buffer

static OSStatus xxx_StopIO(AudioServerPlugInDriverRef inDriver, AudioObjectID inDeviceObjectID, UInt32 inClientID)

//真正的方法

static OSStatus CamStudioAudio_DoIOOperation(....)

里面真正执行任务，接收和发送都在这里完成。
  // virutal device -> Other Captured
    if(inOperationID == kAudioServerPlugInIOOperationReadInput)
    {
        return sendDataToOtherApp(inIOBufferFrameSize, inIOCycleInfo, ioMainBuffer);
    }
    
    // other app -> virutal device
    if(inOperationID == kAudioServerPlugInIOOperationWriteMix)
    {
        return getDataFromOtherApp(inIOBufferFrameSize, inIOCycleInfo, ioMainBuffer);
    }

//这个函数可以不管

static OSStatus xxx_EndIOOperation(...)

2. CoreAudio 驱动

//准备获取ID

    AudioObjectPropertyAddress address = makeOutputPropertyAddress(kAudioHardwarePropertyDevices);
    UInt32 devicesDataSize;
    //获取具体列表的内存大小
    OSStatus status = AudioObjectGetPropertyDataSize(kAudioObjectSystemObject,
      &address,
      0,
      NULL,
      &devicesDataSize);
    RETBOOL(status, "findMyAudioDevice-AudioObjectGetPropertyDataSize")
    //判断长度，并请求填充内存
    int count = devicesDataSize / sizeof(AudioDeviceID);
    AudioDeviceID deviceIDs[count];
    status = AudioObjectGetPropertyData(kAudioObjectSystemObject,
                                        &address,
                                        0,
                                        NULL,
                                        &devicesDataSize,
                                        deviceIDs);
    //轮询列表获取合适的id
    AudioObjectGetPropertyData(deviceID, &address, 0, NULL,  &size, &prop);
    
    //创建和析构监听
    AudioObjectAddPropertyListener(...kAudioDevicePropertyDeviceIsAlive)
    AudioObjectRemovePropertyListener(...kAudioDevicePropertyNominalSampleRate)

#import

#import

//绑定

OSStatus status = AudioDeviceCreateIOProcID(设备ID, deviceIOProcFunc/*回调函数*/, this, &mDeviceIOProcID/*创建的io句柄*/);

//开始

OSStatus status = AudioDeviceStart(mDevice.getNeedID(), mDeviceIOProcID);

//回调

。。。

//销毁

AudioDeviceDestroyIOProcID(mDevice.getNeedID(), mDeviceIOProcID);

3. AudioConvertRef 转码

头文件 #include

 //创建转换对象
    AudioConverterRef audioConverter;
    AudioConverterNew(&_inASBD, &_outASBD, &audioConverter);

//重新从 Audio Convert 获取被校正过的 ASBD数据

AudioConverterGetProperty(audioConverter, kAudioConverterCurrentInputStreamDescription, &size, &_inASBD);

//将获取的MagicCookie 设置到 converter 中

AudioConverterSetProperty(converter,kAudioConverterDecompressionMagicCookie,cookieDataSize,cookieData),

//计算输入缓冲区的大小，及缓冲区能容纳的packet 数量

_inBuffer = malloc(4096*8)

//vbr 需要从文件中读取。kAudioFilePropertyPacketSizeUpperBound是预估不是打开计算

AudioFileGetProperty(_inFile, kAudioFilePropertyPacketSizeUpperBound, &size, &inSizePerPacket)

//计算和开辟输出缓冲区

//vbr得到最大输入的每包最大输出大小

AudioConverterGetProperty(audioConverter, kAudioConverterPropertyMaximumOutputPacketSize, &size, outData);

//写入Magic cookie

status = AudioConverterGetProperty(converter, kAudioConverterDecompressionMagicCookie, &cookieDataSize, cookies);
status = AudioFileSetProperty(_outFile, kAudioFilePropertyMagicCookieData, cookieDataSize, cookies);

//死循环进行数据转换

AudioConverterFillComplexBuffer(....) //会在这里的回调里面填充input数据，内部进行转换，返回值之后，获取到的就是转换后的数据

AudioFileWritePackets 写入文件

outFilePacketOffset += ioOutDataPacketsPerOut;//下次输出文件的时候，需要增加这次输出的数量

AudioConverterDispose(audioConverter)//关闭和释放AudioConverter的资源

4. AudioQueue output 输出

//创建Audioqueue对象，并配置callback
  AudioQueueNewOutput(&inASBD,
                                          callback,
                                          UnsafeMutableRawPointer(Unmanaged.passUnretained(self).toOpaque()),
                                          nil,
                                          nil,
                                          0,
                                          &self.audioQueue)

//自定义输出设备，如果不想用默认的话
       var cuStr = "FC-E8-06-DB-74-1D:output" as CFString
       AudioQueueSetProperty(self.audioQueue!, kAudioQueueProperty_CurrentDevice, &cuStr, size)

//获取输出设备的 asbd， 方便后面转码
AudioQueueGetProperty(self.audioQueue!, kAudioQueueProperty_StreamDescription, &outADSB, &size)

//创建三个默认的Audioqueue队列。并塞入静音数据，手动调用一次callback
        for _ in 0..
            var buffer: AudioQueueBufferRef?
            AudioQueueAllocateBuffer(self.audioQueue!,
    self.byteSizeInBuffer,
    &buffer)
            //往buffer 中填充默认的静音数据
            let buf = UnsafeMutableRawPointer.allocate(byteCount: Int(self.byteSizeInBuffer), alignment: 1)
            memset(buf, 0, Int(self.byteSizeInBuffer))
            TPCircularBufferProduceBytes(&self.tpBuffer, buf, self.byteSizeInBuffer)
            buf.deallocate()
            
            callback(UnsafeMutableRawPointer(Unmanaged.passUnretained(self).toOpaque()), self.audioQueue!, buffer!)
        }

//正式开始
AudioQueueStart(self.audioQueue!, nil)

//开始后会自动回调callback
    private let callback: AudioQueueOutputCallback = {
        inUserData, queue,  bufferRef in
        
       .... //判断数据是否足够，从circle bufer拿出数据，进行转码
	
	   //将合适的格式大小的数据，塞入播放队列
       AudioQueueEnqueueBuffer(queue,
                                              bufferRef,
                                              0,
                                              nil)
    }

            //stop
            AudioQueueStop(self.audioQueue!, true)
            AudioQueueDispose(self.audioQueue!, true)

5. AudioQueue 采集

  //创建 queue
    JBAssertNoError(AudioQueueNewInput(&_mDataFormat,
                                       captureAudioDataCallback,
                                       (__bridge void *)(self),
                                       NULL,
                                       kCFRunLoopCommonModes,
                                       0,
                                       &_mQueue),
//获取asbd
  AudioQueueGetProperty(_mQueue,kAudioQueueProperty_StreamDescription,&_mDataFormat,&size),
  //内存分配，入队
    for (int i = 0; i != KNumberBuffers; i++ ){
        JBAssertNoError(AudioQueueAllocateBuffer(_mQueue, bufferByteSize, &_mBuffers[i]), @"AudioQueueAllocateBuffer");
        JBAssertNoError(AudioQueueEnqueueBuffer(_mQueue, _mBuffers[i], 0, NULL), @"AudioQueueEnqueueBuffer");
    }
    //启动audio queue , 第二个参数设置为NULL表示立即开始采集数据.
    JBAssertNoError(AudioQueueStart(_mQueue, NULL), @"AudioQueueStart");
static void captureAudioDataCallback(void *__nullable  inUserData,...) {
//写入和拷贝数据
...
//释放队列
	AudioQueueEnqueueBuffer(inAQ, inBuffer, 0, NULL),
}
//关闭
        JBAssertNoError(AudioQueueStop(_mQueue, true),@"AudioQueueStop");
        JBAssertNoError(AudioQueueDispose(_mQueue, true), @"AudioQueueDispose");

6. AudioUnit 采集