在iOS上Audio Unit是比较底层的接口，可以理解为其是对音频硬件驱动的封装。用来进行低延迟的音频采集和播放功能如实时语音、VoIP的场景。
iOS提供了2中创建AudioUnit。一种直接创建AudioUnit、一种通过AUGraph创建AudioUnit.
一般我们再开发过程中多数会用到AUGraph创建AudioUnit，减少在特性需求下的工作量。
1、AVAudioSession 设置上下文信息
在设置session中如果设置采样率，那么在不同的录音设备20ms录制的字节数都为恒定值，项目中未设置，根据设备动态配置录音的字节。
- (Boolean)setupAuidoSession {
NSError *error = nil;
AVAudioSession *session = [AVAudioSession sharedInstance];
[session setCategory:AVAudioSessionCategoryPlayAndRecord withOptions:AVAudioSessionCategoryOptionAllowBluetooth error:&error];
if (error != nil) {
NSLog(@"setupAudioSession : Error set AVAudioSessionCategoryOptionAllowBluetooth(%@).", error.localizedDescription);
return false;
}
float aBufferLength = 0.02;
[session setPreferredIOBufferDuration:aBufferLength error:&error];
//在audioSession中设置首选采样率，那么无论什么设备采样率是一致的，不会根据设备而变化。如果不设置那么在录制回调中inNumberFrames值会不同，意味着在此需要使用循环处理数据
[session setPreferredSampleRate:kSampleRate error:nil];
if (error != nil) {
NSLog (@"setupAudioSession : Error setPreferredIOBufferDuration(%@).", error.localizedDescription);
return false;
}
//增加中断监听
[[NSNotificationCenter defaultCenter] addObserver:self
selector:@selector(handleInterruption:)
name:AVAudioSessionInterruptionNotification
object:session];
[session setActive:YES withOptions:AVAudioSessionSetActiveOptionNotifyOthersOnDeactivation error: &error];
if (nil != error) {
NSLog(@"AudioSession setActive error:%@", error.localizedDescription);
return false;
}
return true;
}
2、设置AudioUnit
- (Boolean)setupAudioUnit {
//生成AudioComponentInstance实例
AudioComponentDescription audioDes;
audioDes.componentType = kAudioUnitType_Output;
audioDes.componentSubType = kAudioUnitSubType_RemoteIO;
audioDes.componentManufacturer = kAudioUnitManufacturer_Apple;
audioDes.componentFlags = 0;
audioDes.componentFlagsMask = 0;
AudioComponent inputComponent = AudioComponentFindNext(NULL, &audioDes);
CheckOSStatus(AudioComponentInstanceNew(inputComponent, &ioUnit), "New ComponentInstance Fail");
//创建录制buffer
UInt32 flag = 0;
CheckOSStatus(AudioUnitSetProperty(ioUnit,
kAudioUnitProperty_ShouldAllocateBuffer,
kAudioUnitScope_Output,
1,
&flag,
sizeof(flag)), "could not set StreamFormat");
self->recordAudioBufferList = malloc(sizeof(AudioBufferList));
self->recordAudioBufferList->mNumberBuffers = 1;
self->recordAudioBufferList->mBuffers[0].mNumberChannels = 1;
self->recordAudioBufferList->mBuffers[0].mDataByteSize = 4096;
self->recordAudioBufferList->mBuffers[0].mData = malloc(4096);
//设置音频流格式
AudioStreamBasicDescription audioFormat;
audioFormat.mSampleRate = kSampleRate;
audioFormat.mFormatID = kAudioFormatLinearPCM;
audioFormat.mFormatFlags = kLinearPCMFormatFlagIsSignedInteger | kLinearPCMFormatFlagIsPacked;
audioFormat.mFramesPerPacket = 1;
audioFormat.mChannelsPerFrame = 1;
audioFormat.mBitsPerChannel = 16;
audioFormat.mBytesPerFrame = (audioFormat.mChannelsPerFrame * audioFormat.mBitsPerChannel) / 8;
audioFormat.mBytesPerPacket = audioFormat.mBytesPerFrame * audioFormat.mFramesPerPacket;
CheckOSStatus(AudioUnitSetProperty(ioUnit,
kAudioUnitProperty_StreamFormat,
kAudioUnitScope_Output,
1,
&audioFormat,
sizeof(audioFormat)), "could not set Output StreamFormat");
CheckOSStatus(AudioUnitSetProperty(ioUnit,
kAudioUnitProperty_StreamFormat,
kAudioUnitScope_Input,
0,
&audioFormat,
sizeof(audioFormat)), "could not set Input StreamFormat");
//设置录制回调
AURenderCallbackStruct recordCallback;
recordCallback.inputProc = recordCallbackFunc;
recordCallback.inputProcRefCon = (__bridge void *)self;
CheckOSStatus(AudioUnitSetProperty(ioUnit,
kAudioOutputUnitProperty_SetInputCallback,
kAudioUnitScope_Global,
1,
&recordCallback,
sizeof(recordCallback)), "recordCallback failure");
//打开录音设备
flag = 1;
CheckOSStatus(AudioUnitSetProperty(ioUnit,
kAudioOutputUnitProperty_EnableIO,
kAudioUnitScope_Input,
1,
&flag,
sizeof(flag)), "enable input failure");
return true;
}
3、录音回调
- (AudioBufferList)getBufferList:(UInt32)inNumberFrames {
AudioBuffer buffer;
buffer.mDataByteSize = inNumberFrames * 2;
buffer.mNumberChannels = 1;
buffer.mData = malloc( inNumberFrames * 2 );
AudioBufferList bufferList;
bufferList.mNumberBuffers = 1;
bufferList.mBuffers[0] = buffer;
return bufferList;
}
static OSStatus recordCallbackFunc(void *inRefCon,
AudioUnitRenderActionFlags *ioActionFlags,
const AudioTimeStamp *inTimeStamp,
UInt32 inBusNumber,
UInt32 inNumberFrames,
AudioBufferList *ioData){
YYAudioRecordManager *this = (__bridge YYAudioRecordManager *)inRefCon;
OSStatus err = noErr;
if (this.isRecording){
@autoreleasepool {
AudioBufferList bufList = [this getBufferList:inNumberFrames];
err = AudioUnitRender(this->ioUnit, ioActionFlags, inTimeStamp, inBusNumber, inNumberFrames, &bufList);
if (err) {
printf("AudioUnitRender error code = %d", err);
} else {
AudioBuffer buffer = bufList.mBuffers[0];
this.levels = computeLevel(buffer.mData, buffer.mDataByteSize);
NSData *pcmBlock = [NSData dataWithBytes:buffer.mData length:buffer.mDataByteSize];
[this processAudioData:pcmBlock];
free(buffer.mData);
}
}
}
return err;
}
4、检查组件状态
static bool CheckOSStatus(OSStatus result, const char *operation) {
if (result == noErr) {
return true;
}
char errorString[20];
*(UInt32 *)(errorString + 1) = CFSwapInt32HostToBig(result);
if (isprint(errorString[1]) &&
isprint(errorString[2]) &&
isprint(errorString[3]) &&
isprint(errorString[4])) {
errorString[0] = errorString[5] = '\'';
errorString[6] = '\0';
} else {
sprintf(errorString,"%d",(int)result);
}
fprintf(stderr, "Error: %s (%s)\n", operation, errorString);
return false;
}
5、开始录制
BOOL status = [self setupAuidoSession];
if (status == false) {
return;
}
[self setupAudioUnit];
int result = CheckOSStatus(AudioUnitInitialize(ioUnit), "init unit failure");
if (result < 0) {
return;
}
result = CheckOSStatus(AudioOutputUnitStart(ioUnit), "start unit failure");
if (result < 0) {
return;
}
6、停止录制
AudioOutputUnitStop(ioUnit)
AudioComponentInstanceDispose(ioUnit)
7、暂停录制
AudioOutputUnitStop(ioUnit)
8、继续录制
AudioOutputUnitStart(ioUnit)
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