AudioUnit 用法

1、描述音频单元

AudioComponentDescription desc;
desc.componentType = kAudioUnitType_Output;
desc.componentSubType = kAudioUnitSubType_RemoteIO;
desc.componentFlags = 0;
desc.componentFlagsMask = 0;
desc.componentManufacturer = kAudioUnitManufacturer_Apple;

2、查找音频单元

AudioComponent inputComponent = AudioComponentFindNext(NULL, &desc);

3、获取音频单元实例

status = AudioComponentInstanceNew(inputComponent, &audioUnit);

4、启用录制功能、启用播放功能

UInt32 flag = 1;
status = AudioUnitSetProperty(audioUnit,
                                 kAudioOutputUnitProperty_EnableIO,
                                  kAudioUnitScope_Input,
                                  kInputBus,
                                  &flag,
                                  sizeof(flag));

status = AudioUnitSetProperty(audioUnit,
                                 kAudioOutputUnitProperty_EnableIO,
                                  kAudioUnitScope_Output,
                                  kOutputBus,
                                  &flag,
                                  sizeof(flag));

5、音频流描述

AudioStreamBasicDescription audioFormat;
audioFormat.mSampleRate = 44100.00;
audioFormat.mFormatID = kAudioFormatLinearPCM;
audioFormat.mFormatFlags = kAudioFormatFlagIsSignedInteger | kAudioFormatFlagIsPacked;
audioFormat.mFramesPerPacket = 1;
audioFormat.mChannelsPerFrame = 1;
audioFormat.mBitsPerChannel = 16;
audioFormat.mBytesPerPacket = 2;
audioFormat.mBytesPerFrame = 2;

6、应用录制和播放的音频流描述

status = AudioUnitSetProperty(audioUnit,
                                 kAudioUnitProperty_StreamFormat,
                                  kAudioUnitScope_Output,
                                  kInputBus,
                                  &audioFormat,
                                  sizeof(audioFormat));

status = AudioUnitSetProperty(audioUnit,
                                  kAudioUnitProperty_StreamFormat,
                                  kAudioUnitScope_Input,
                                  kOutputBus,
                                  &audioFormat,
                                  sizeof(audioFormat));

7、设置回调

AURenderCallbackStruct callbackStruct;
callbackStruct.inputProc = recordingCallback;
callbackStruct.inputProcRefCon = self;
status = AudioUnitSetProperty(audioUnit,
                                kAudioOutputUnitProperty_SetInputCallback,
                                kAudioUnitScope_Global,
                                kInputBus,
                                &callbackStruct,
                                sizeof(callbackStruct));

callbackStruct.inputProc = playbackCallback;
callbackStruct.inputProcRefCon = self;
status = AudioUnitSetProperty(audioUnit,
                                kAudioUnitProperty_SetRenderCallback,
                                kAudioUnitScope_Global,
                                kOutputBus,
                                &callbackStruct,
                                sizeof(callbackStruct));

8、回调方法

static OSStatus recordingCallback(void *inRefCon,
                                  AudioUnitRenderActionFlags*ioActionFlags,
                                  const AudioTimeStamp*inTimeStamp,
                                  UInt32 inBusNumber,
                                  UInt32 inNumberFrames,
                                  AudioBufferList *ioData) {

    AudioBufferList *bufferList;     

    OSStatus status = AudioUnitRender([(shockmanViewController*)inRefCon audioUnit],  ioActionFlags, inTimeStamp, inBusNumber, inNumberFrames, bufferList);

    return noErr;

}

static OSStatus playbackCallback(void *inRefCon,
                                 AudioUnitRenderActionFlags*ioActionFlags,
                                 const AudioTimeStamp*inTimeStamp,
                                 UInt32 inBusNumber,
                                 UInt32 inNumberFrames,
                                 AudioBufferList *ioData) {
    // This is a mono tone generator so we only need the first buffer
    UInt16 *buffer = (SAMPLE *)ioData->mBuffers[0].mData;
    // Generate the samples
    for (UInt32 frame = 0; frame < inNumberFrames; frame++)
    {
        if(THIS->isPlaying) {
　　　　// 通过修改buffer数组的值，输出自己的音频数据
            buffer[frame] = audioProtocol.getEncode()[THIS->qIndex++];
            if(THIS->qIndex >= THIS->qSize) {
                //[THIS stopToPlay];
                [THIS performSelectorOnMainThread:@selector(stopToPlay) withObject:nil waitUntilDone:NO];
                break;
            }
        }
    }

    return noErr;

}