AudioUnit随笔

作者: DontBB码一下 | 来源:发表于2019-04-02 15:22 被阅读0次

AudioUnit

该主要在MAC上的音频APP实现中并且需要最大限度的实时性能的情况下使用，大部分音频APP不需要使用该层的服务。而且，在iOS上也提供了具备较高实时性能的高层API达到你的需求。例如OpenAL，在游戏中具备与I/O直接调用的实时音频处理能力。

I/O Kit, 与硬件驱动交互

Audio HAL, 音频硬件抽象层，使API调用与实际硬件相分离，保持独立

Core MIDI, 为MIDI流和设备提供软件抽象工作层

Host Time Services, 访问电脑硬件时钟

1.2 Mid-Level

该层功能比较齐全，包括音频数据格式转换，音频文件读写，音频流解析，插件工作支持等。

Audio Convert Services 负责音频数据格式的转换

Audio File Services 负责音频数据的读写

Audio Unit Services 和 Audio Processing Graph Services 支持均衡器和混音器等数字信号处理的插件

Audio File Scream Services 负责流解析

Core Audio Clock Services 负责音频音频时钟同步

1.3 High-Level

是一组从低层接口组合起来的高层应用，基本上我们很多关于音频开发的工作在这一层就可以完成

Audio Queue Services 提供录制、播放、暂停、循环、和同步音频它自动采用必要的编解码器处理压缩的音频格式

AVAudioPlayer 是专为IOS平台提供的基于Objective-C接口的音频播放类，可以支持iOS所支持的所有音频的播放

Extended Audio File Services 由Audio File与Audio Converter组合而成，提供压缩及无压缩音频文件的读写能力

OpenAL 是CoreAudio对OpenAL标准的实现，可以播放3D混音效果

2.1 AudioUnit类型

I/O: Remote I/O、Voice-Processing I/O、Generic Output

Mixing: 3D Mixer、Mutichannel Mixer

Effect: iPod Equalizer

Format Conversion: Format Converter

每个AudioUnit都有Input, Output 和 Global 三个域。input输入域是音频流进入unit的入口，output输出域是音频流离开unit的出口，global全局域则代表整个unit。输入域和输出域都有若干个bus/element，比如说mixer unit有多个输入bus，只有一个输出bus；而splitter unit则有一个输入bus，有多个输出的bus。其中，I/O主要负责和设备打交道，比如采集和播放;Mixing负责将不同来源的音频数据进行混合;Effect是对音频数据进行音效处理（变声、混响）;Format Conversion主要是进行格式转换比如重采样等。这里有一个优化的点是音频格式转换 Multichannel Mixer 本身就能够实现格式转换的功能，输入和输出的音频数据格式可以不同，利用这一点可以节省一个格式转换unit。

2.2 AudioUnit创建方式

I/O Unit

先来了解一下第一种创建方式中要用的结构体类型

//此结构体用来描述Audio的基本信息
struct AudioStreamBasicDescription    
{
    Float64            mSampleRate;
    AudioFormatID      mFormatID;
    AudioFormatFlags    mFormatFlags;
    UInt32              mBytesPerPacket;
    UInt32              mFramesPerPacket;
    UInt32              mBytesPerFrame;
    UInt32              mChannelsPerFrame;
    UInt32              mBitsPerChannel;
    UInt32              mReserved;
};
//缓冲区Data
struct AudioBuffer
{
    UInt32              mNumberChannels;
    UInt32              mDataByteSize;
    void* __nullable    mData;
};
//缓冲区List
struct AudioBufferList
{
    UInt32      mNumberBuffers;
    AudioBuffer mBuffers[1]; // this is a variable length array of mNumberBuffers elements
    
#if defined(__cplusplus) && defined(CA_STRICT) && CA_STRICT
public:
    AudioBufferList() {}
private:
    //  Copying and assigning a variable length struct is problematic; generate a compile error.
    AudioBufferList(const AudioBufferList&);
    AudioBufferList&    operator=(const AudioBufferList&);
#endif

};
//Audio元素描述
typedef struct AudioComponentDescription {
    OSType              componentType;
    OSType              componentSubType;
    OSType              componentManufacturer;
    UInt32              componentFlags;
    UInt32              componentFlagsMask;
} AudioComponentDescription;

容易混淆的概念
kAudioUnitProperty_SetRenderCallback是audio unit需要数据，向Host请求数据；
kAudioOutputUnitProperty_SetInputCallback是audio unit通知Host数据已经就绪，可以通过AudioUnitRender拉取数据；
MaximumFramesPerSlice 表示的是每次回调送入或取出的音频数据的长度

下面就送上第一个实现的代码吧




// create IO Unit

    BOOL result = NO;

AudioComponentDescriptionoutputDescription = {0};

    outputDescription.componentType = kAudioUnitType_Output;

    outputDescription.componentSubType = kAudioUnitSubType_RemoteIO;

    outputDescription.componentManufacturer = kAudioUnitManufacturer_Apple;

    outputDescription.componentFlags = 0;

    outputDescription.componentFlagsMask = 0;

AudioComponent comp = AudioComponentFindNext(NULL, &outputDescription);

result = CheckOSStatus(AudioComponentInstanceNew(comp, &mVoipUnit), @"couldn't create a new instance of RemoteIO");

    if (!result) return result;



    // config IO Enable status

    UInt32 flag = 1;

result = CheckOSStatus(AudioUnitSetProperty(mVoipUnit, kAudioOutputUnitProperty_EnableIO, kAudioUnitScope_Output, kOutputBus, &flag, sizeof(flag)), @"could not enable output on RemoteIO");

    if (!result) return result;

   ///以下设置可以理解为设置element 1的input_scope的EnableIO的属性值是&flag

    result = CheckOSStatus(AudioUnitSetProperty(mVoipUnit, kAudioOutputUnitProperty_EnableIO, kAudioUnitScope_Input, kInputBus, &flag, sizeof(flag)),                  @"AudioUnitSetProperty EnableIO");

    if (!result) return result;



    // Config default format

    result = CheckOSStatus(AudioUnitSetProperty(mVoipUnit, kAudioUnitProperty_StreamFormat, kAudioUnitScope_Output, kInputBus, &inputAudioDescription, sizeof(inputAudioDescription)), @"couldn't set the input client format on RemoteIO");

    if (!result) return result;

    result = CheckOSStatus(AudioUnitSetProperty(mVoipUnit, kAudioUnitProperty_StreamFormat, kAudioUnitScope_Input, kOutputBus, &outputAudioDescription, sizeof(outputAudioDescription)), @"couldn't set the output client format on RemoteIO");

    if (!result) return result;

 // Set the MaximumFramesPerSlice property. This property is used to describe to an audio unit the maximum number

    // of samples it will be asked to produce on any single given call to AudioUnitRender

    UInt32 maxFramesPerSlice = 4096;

    result = CheckOSStatus(AudioUnitSetProperty(mVoipUnit, kAudioUnitProperty_MaximumFramesPerSlice, kAudioUnitScope_Global, 0, &maxFramesPerSlice, sizeof(UInt32)), @"couldn't set max frames per slice on RemoteIO");

    if (!result) return result;



    // Set the record callback

AURenderCallbackStructrecordCallback;

    recordCallback.inputProc = recordCallbackFunc;

    recordCallback.inputProcRefCon = (__bridge void * _Nullable)(self);

result = CheckOSStatus(AudioUnitSetProperty(mVoipUnit, kAudioOutputUnitProperty_SetInputCallback, kAudioUnitScope_Global, kInputBus, &recordCallback, sizeof(recordCallback)), @"couldn't set record callback on RemoteIO");

    if (!result) return result;



    // Set the playback callback

AURenderCallbackStructplaybackCallback;

    playbackCallback.inputProc = playbackCallbackFunc;

    playbackCallback.inputProcRefCon = (__bridge void * _Nullable)(self);

result = CheckOSStatus(AudioUnitSetProperty(mVoipUnit, kAudioUnitProperty_SetRenderCallback, kAudioUnitScope_Global, kOutputBus, &playbackCallback, sizeof(playbackCallback)), @"couldn't set playback callback on RemoteIO");

    if (!result) return result;



    // set buffer allocate

    flag = 0;

    result = CheckOSStatus(AudioUnitSetProperty(mVoipUnit,

                                                kAudioUnitProperty_ShouldAllocateBuffer,

                                                kAudioUnitScope_Output,

                                                kInputBus,

                                                &flag,

                                                sizeof(flag)), @"couldn't set property for ShouldAllocateBuffer");

    if (!result) return result;

 // Initialize the output IO instance

    result = CheckOSStatus(AudioUnitInitialize(mVoipUnit), @"couldn't initialize VoiceProcessingIO instance");

    if (!result) return result;



    return YES;

AUGraph

AUGraph实现流程如下：

1、初始化文件流和AVAudioSession，分配buffer；
2、新建AUGraph，并添加两个AUNode，一个是RemoteI/O Unit的节点，一个是Mixer Unit的节点。添加AUNode的节点有两个步骤，先通过AUGraphAddNode添加节点，再通过AUGraphNodeInfo获取节点对应的AudioUnit。
3、建立两个AUNode的联系，AUGraphConnectNodeInput通过把Mixer Unit的outputBus的输出作为RemoteI/O Unit的outputBus的输入；（这里需要注意，不是RemoteI/O的inputBus 的输入，因为RemoteI/O Unit的inputBus的输入是麦克风）同时设置好RemoteI/O Unit的输入和输出格式、Record的回调函数；
4、调用AUGraphInitialize初始化AUGraph，然后通过AUGraphStart开始整个AUGraph;在AUGraph开启后，麦克风收到录制数据后调kAudioOutputUnitProperty_SetInputCallback的回调，把麦克风的数据回调给APP；Mixer Unit kAudioUnitProperty_SetRenderCallback设置好的回调，要求APP填充两个inputBus的输入；在Mixer Unit处理好数据之后，会按照之前AUGraphConnectNodeInput设置的，把数据发送给Remote I/O Unit；Remote I/O Unit再把数据发送给扬声器。

// create AUGraph
    BOOL result = NO;
    result = CheckOSStatus(NewAUGraph (&processingGraph), @"couldn't create a new instance of AUGraph");
    if (!result) return result;
    
    // I/O unit
    AudioComponentDescription iOUnitDescription;
    iOUnitDescription.componentType          = kAudioUnitType_Output;
    iOUnitDescription.componentSubType       = kAudioUnitSubType_RemoteIO;
    iOUnitDescription.componentManufacturer  = kAudioUnitManufacturer_Apple;
    iOUnitDescription.componentFlags         = 0;
    iOUnitDescription.componentFlagsMask     = 0;
    
    // Multichannel mixer unit
    AudioComponentDescription MixerUnitDescription;
    MixerUnitDescription.componentType          = kAudioUnitType_Mixer;
    MixerUnitDescription.componentSubType       = kAudioUnitSubType_MultiChannelMixer;
    MixerUnitDescription.componentManufacturer  = kAudioUnitManufacturer_Apple;
    MixerUnitDescription.componentFlags         = 0;
    MixerUnitDescription.componentFlagsMask     = 0;
    
    AUNode   iONode;         // node for I/O unit
    AUNode   mixerNode;      // node for Multichannel Mixer unit
    
    result = CheckOSStatus(AUGraphAddNode (
                                           processingGraph,
                                           &iOUnitDescription,
                                           &iONode), @"couldn't add a node instance of kAudioUnitSubType_RemoteIO");
    if (!result) return result;
result = CheckOSStatus(AUGraphAddNode (
                                           processingGraph,
                                           &MixerUnitDescription,
                                           &mixerNode), @"couldn't add a node instance of mixer unit");
    if (!result) return result;
    
    // open the AUGraph
    result = CheckOSStatus(AUGraphOpen (processingGraph), @"couldn't get instance of mixer unit");
    if (!result) return result;
    
    // Obtain unit instance
    result = CheckOSStatus(AUGraphNodeInfo (
                                            processingGraph,
                                            mixerNode,
                                            NULL,
                                            &mMixerUnit
                                            ), @"couldn't get instance of mixer unit");
    if (!result) return result;
    
    result = CheckOSStatus(AUGraphNodeInfo (
                                            processingGraph,
                                            iONode,
                                            NULL,
                                            &mVoipUnit
                                            ), @"couldn't get a new instance of remoteio unit");
    if (!result) return result;
 UInt32 busCount   = 2;    // bus count for mixer unit input
    UInt32 guitarBus  = 0;    // mixer unit bus 0 will be stereo and will take the guitar sound
    UInt32 beatsBus   = 1;    // mixer unit bus 1 will be mono and will take the beats sound
    result = CheckOSStatus(AudioUnitSetProperty (
                                                 mMixerUnit,
                                                 kAudioUnitProperty_ElementCount,
                                                 kAudioUnitScope_Input,
                                                 0,
                                                 &busCount,
                                                 sizeof (busCount)
                                                 ), @"could not set mixer unit input bus count");
    if (!result) return result;
    
    UInt32 maximumFramesPerSlice = 4096;
    result = CheckOSStatus(AudioUnitSetProperty (
                                                 mMixerUnit,
                                                 kAudioUnitProperty_MaximumFramesPerSlice,
                                                 kAudioUnitScope_Global,
                                                 0,
                                                 &maximumFramesPerSlice,
                                                 sizeof (maximumFramesPerSlice)
                                                 ), @"could not set mixer unit maximum frame per slice");
    if (!result) return result;
    
     // Attach the input render callback and context to each input bus
    for (UInt16 busNumber = 0; busNumber < busCount; ++busNumber) {
        
        // Setup the struture that contains the input render callback
        AURenderCallbackStruct playbackCallback;
        playbackCallback.inputProc = playbackCallbackFunc;
        playbackCallback.inputProcRefCon = (__bridge void * _Nullable)(self);
        
        NSLog (@"Registering the render callback with mixer unit input bus %u", busNumber);
        // Set a callback for the specified node's specified input
        result = CheckOSStatus(AUGraphSetNodeInputCallback (
                                                            processingGraph,
                                                            mixerNode,
                                                            busNumber,
                                                            &playbackCallback
                                                            ), @"couldn't set playback callback on mixer unit");
        if (!result) return result;
    }
 // Config mixer unit input default format
    result = CheckOSStatus(AudioUnitSetProperty (
                                                 mMixerUnit,
                                                 kAudioUnitProperty_StreamFormat,
                                                 kAudioUnitScope_Input,
                                                 guitarBus,
                                                 &outputAudioDescription,
                                                 sizeof (outputAudioDescription)
                                                 ), @"couldn't set the input 0 client format on mixer unit");
    if (!result) return result;
    
    result = CheckOSStatus(AudioUnitSetProperty (
                                                 mMixerUnit,
                                                 kAudioUnitProperty_StreamFormat,
                                                 kAudioUnitScope_Input,
                                                 beatsBus,
                                                 &outputAudioDescription,
                                                 sizeof (outputAudioDescription)
                                                 ), @"couldn't set the input 1 client format on mixer unit");
    if (!result) return result;
 Float64 graphSampleRate = 44100.0;    // Hertz;
    result = CheckOSStatus(AudioUnitSetProperty (
                                                 mMixerUnit,
                                                 kAudioUnitProperty_SampleRate,
                                                 kAudioUnitScope_Output,
                                                 0,
                                                 &graphSampleRate,
                                                 sizeof (graphSampleRate)
                                                 ), @"couldn't set the output client format on mixer unit");
    if (!result) return result;
    
    ////////////////////////////////////////////////////////////////////////////////////////////
    
    // config void unit IO Enable status
    UInt32 flag = 1;
    result = CheckOSStatus(AudioUnitSetProperty(mVoipUnit,
                                                kAudioOutputUnitProperty_EnableIO,
                                                kAudioUnitScope_Output,
                                                kOutputBus,
                                                &flag,
                                                sizeof(flag)
                                                ), @"could not enable output on kAudioUnitSubType_RemoteIO");
    if (!result) return result;
 result = CheckOSStatus(AudioUnitSetProperty(mVoipUnit,
                                                kAudioOutputUnitProperty_EnableIO,
                                                kAudioUnitScope_Input,
                                                kInputBus,
                                                &flag,
                                                sizeof(flag)
                                                ), @"could not enable input on kAudioUnitSubType_RemoteIO");
    if (!result) return result;
    
    // config voip unit default format
    result = CheckOSStatus(AudioUnitSetProperty(mVoipUnit,
                                                kAudioUnitProperty_StreamFormat,
                                                kAudioUnitScope_Output,
                                                kInputBus,
                                                &inputAudioDescription,
                                                sizeof(inputAudioDescription)
                                                ), @"couldn't set the input client format on kAudioUnitSubType_RemoteIO");
    if (!result) return result;
 UInt32 maxFramesPerSlice = 4096;
    result = CheckOSStatus(AudioUnitSetProperty(mVoipUnit,
                                                kAudioUnitProperty_MaximumFramesPerSlice,
                                                kAudioUnitScope_Global,
                                                0,
                                                &maxFramesPerSlice,
                                                sizeof(UInt32)
                                                ), @"couldn't set max frames per slice on kAudioUnitSubType_RemoteIO");
    if (!result) return result;
    
    // Set the record callback
    AURenderCallbackStruct recordCallback;
    recordCallback.inputProc = recordCallbackFunc;
    recordCallback.inputProcRefCon = (__bridge void * _Nullable)(self);
    result = CheckOSStatus(AudioUnitSetProperty(mVoipUnit,
                                                kAudioOutputUnitProperty_SetInputCallback,
                                                kAudioUnitScope_Global,
                                                kInputBus,
                                                &recordCallback,
                                                sizeof(recordCallback)
                                                ), @"couldn't set record callback on kAudioUnitSubType_RemoteIO");
    if (!result) return result;
 // set buffer allocate
    flag = 0;
    result = CheckOSStatus(AudioUnitSetProperty(mVoipUnit,
                                                kAudioUnitProperty_ShouldAllocateBuffer,
                                                kAudioUnitScope_Output,
                                                kInputBus,
                                                &flag,
                                                sizeof(flag)), @"couldn't set property for ShouldAllocateBuffer");
    if (!result) return result;
    
    /////////////////////////////////////////////////////////////////////////////////////////////
    // Initialize the output IO instance
    result = CheckOSStatus(AUGraphConnectNodeInput (
                                                    processingGraph,
                                                    mixerNode,         // source node
                                                    0,                 // source node output bus number
                                                    iONode,            // destination node
                                                    0                  // desintation node input bus number
                                                    ), @"couldn't connect ionode to mixernode");
    if (!result) return result;
    
    result = CheckOSStatus(AUGraphInitialize (processingGraph), @"AUGraphInitialize failed");
    if (!result) return result;

    return YES;

AudioUnit随笔

目录

1.1 Low-Level

1.2 Mid-Level

1.3 High-Level

2.1 AudioUnit类型

2.2 AudioUnit创建方式

AUGraph实现流程如下：

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