来自麦克风的 iPhone 核心音频数据为 NaN

Question

当我通过核心音频从麦克风接收数据时，有时缓冲区内只有一个样本，有时有 20 个样本。有时样本的值为 0.00000，有时它们的值为 NaN，有时，它们是您所期望的。

问题是什么？

这是我的代码：

-(void)startListeningWithFrequency:(float)frequency;
{
OSStatus status;
//AudioComponentInstance audioUnit;
AudioComponentDescription desc;
desc.componentType = kAudioUnitType_Output;
desc.componentSubType = kAudioUnitSubType_RemoteIO;
desc.componentFlags = 0;
desc.componentFlagsMask = 0;
desc.componentManufacturer = kAudioUnitManufacturer_Apple;

AudioComponent inputComponent = AudioComponentFindNext(NULL, &desc);
status = AudioComponentInstanceNew( inputComponent, &audioUnit);
checkStatus(status);

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

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

status = AudioUnitSetProperty(audioUnit,
                              kAudioUnitProperty_StreamFormat,
                              kAudioUnitScope_Output,
                              kInputBus,
                              &audioFormat, 
                              sizeof(audioFormat));
checkStatus(status);
//status = AudioUnitSetProperty(audioUnit, 
//                            kAudioUnitProperty_StreamFormat, 
//                            kAudioUnitScope_Input, 
//                            kOutputBus, 
//                            &audioFormat, 
//                            sizeof(audioFormat));
checkStatus(status);
AURenderCallbackStruct callbackStruct;
callbackStruct.inputProc = recordingCallback;
callbackStruct.inputProcRefCon = self;
status = AudioUnitSetProperty(audioUnit, 
                              kAudioOutputUnitProperty_SetInputCallback,
                              kAudioUnitScope_Global,
                              kInputBus, &callbackStruct, sizeof(callbackStruct));
checkStatus(status);
/*  UInt32 shouldAllocateBuffer = 1;
AudioUnitSetProperty(audioUnit, kAudioUnitProperty_ShouldAllocateBuffer, kAudioUnitScope_Global, 1, &shouldAllocateBuffer, sizeof(shouldAllocateBuffer));
*/
//float bufferLength = 0.005;
//AudioSessionSetProperty(kAudioSessionProperty_PreferredHardwareIOBufferDuration, sizeof(bufferLength), &bufferLength);
status = AudioOutputUnitStart(audioUnit);

}

和回调：

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

buffer.mNumberChannels = 1;
buffer.mDataByteSize = inNumberFrames * 2;
NSLog(@"%d",inNumberFrames);
buffer.mData = malloc( inNumberFrames * 2 );

// Put buffer in a AudioBufferList
AudioBufferList bufferList;
bufferList.mNumberBuffers = 1;
bufferList.mBuffers[0] = buffer;



OSStatus status;
status = AudioUnitRender(audioUnit, 
                         ioActionFlags, 
                         inTimeStamp, 
                         inBusNumber, 
                         inNumberFrames, 
                         &bufferList);  
checkStatus(status);
double *q = (double *)(&bufferList)->mBuffers[0].mData;
for(int i=0; i < strlen((const char *)(&bufferList)->mBuffers[0].mData); i++)
{
    //i sometimes doesn't get past 0, sometimes goes into 20s
    NSLog(@"%f",q[i]);//returns NaN, 0.00, or some times actual data
}
}

任何帮助将不胜感激， 谢谢你， 诺诺诺

Answer 1

由于您传递的是流格式的 kAudioFormatFlagIsSignedInteger 标志，因此您的样本就是：16 位有符号整数 (int16_t) 而不是浮点数。您需要以这种方式处理样本，或者使用 kAudioFormatFlagIsFloat 标志（并且您需要使用 float 而不是 double 作为数据类型， AFAIK）。