Audio Processing Graphs 管理 Audio Units

以下是一个使用Audio Unit Framework处理音频的简单示例。这个例子展示了如何设置和连接一个Remote I/O Audio Unit，它是一个常用于实时音频处理的Audio Unit。

import AudioUnit
import AudioToolbox
 
func setupAndRenderAudio() {
    var audioUnit: AudioUnit?
    
    // 设置Audio Component
    let audioComponentDescription = AudioComponentDescription(
        componentType: kAudioUnitType_Generator,
        componentSubType: kAudioUnitSubType_RemoteIORender,
        componentManufacturer: kAudioUnitManufacturer_Apple,
        componentFlags: 0,
        componentFlagsMask: 0)
    
    // 获取Audio Unit
    let status = AudioComponentInstanceNew(audioComponentDescription, &audioUnit)
    
    guard status == noErr else {
        print("无法获取Audio Unit")
        return
    }
    
    // 初始化Audio Unit
    status = AudioUnitInitialize(audioUnit!)
    
    guard status == noErr else {
        print("无法初始化Audio Unit")
        return
    }
    
    // 设置音频格式（例如，这里设置为32位浮点非整数PCM）
    var audioFormat = AudioStreamBasicDescription(
        mSampleRate: 44100,
        mFormatID: kAudioFormatLinearPCM,
        mFormatFlags: kAudioFormatFlagIsFloat | kAudioFormatFlagIsNonInterleaved,
        mBytesPerPacket: 8,
        mFramesPerPacket: 1,
        mBytesPerFrame: 4,
        mChannelsPerFrame: 2,
        mBitsPerChannel: 32,
        mReserved: 0)
    
    // 设置音频格式
    var propertySize: UInt32 = UInt32(MemoryLayout<AudioStreamBasicDescription>.size)
    status = AudioUnitSetProperty(audioUnit!,
                                  kAudioUnitProperty_StreamFormat,
                                  kAudioUnitScope_Input,
                                  0,
                                  &audioFormat,
                                  propertySize)
    
    guard status == noErr else {
        print("无法设置音频格式")
        return
    }
    
    // 准备Audio Unit进行音频渲染
    status = AudioUnitRender(audioUnit!,
                             AudioUnitRenderActionFlags(kAudioUnitRenderAction_Render),
                             &timeStamp,
                             busNumber,
                             audioBufferList)
    
    guard status == noErr else {
        print("无法渲染音频")
        return
    }