使用ExtAudioFileWrite for iOS将音频样本的缓冲区写入aac文件

好吧，经过一番探索，我已经弄明白了。我把它包装成一个函数，将随机噪声写入文件。具体来说，它可以：

• 写入.wav或.m4a文件
• 以任一格式编写单声道或立体声
• 将文件写入指定的路径

函数参数为：

• 要创建的音频文件的路径
• 通道数量(最多2个)
• boolean：使用m4a压缩(如果为false，则使用pcm)

对于立体声M4A文件，函数应调用为：

writeNoiseToAudioFile("/path/to/my/audiofile.m4a",2,true);

函数的来源如下。我试着尽可能多地评论它——我希望它是正确的，它当然对我有效，但如果我错过了什么，请说"亚当，你做错了一点"。祝你好运这是代码：

void writeNoiseToAudioFile(char *fName,int mChannels,bool compress_with_m4a)
{
OSStatus err; // to record errors from ExtAudioFile API functions
// create file path as CStringRef
CFStringRef fPath;
fPath = CFStringCreateWithCString(kCFAllocatorDefault,
fName,
kCFStringEncodingMacRoman);

// specify total number of samples per channel
UInt32 totalFramesInFile = 100000;      
/////////////////////////////////////////////////////////////////////////////
////////////// Set up Audio Buffer List For Interleaved Audio ///////////////
/////////////////////////////////////////////////////////////////////////////
AudioBufferList outputData; 
outputData.mNumberBuffers = 1;
outputData.mBuffers[0].mNumberChannels = mChannels;    
outputData.mBuffers[0].mDataByteSize = sizeof(AudioUnitSampleType)*totalFramesInFile*mChannels;

/////////////////////////////////////////////////////////////////////////////
//////// Synthesise Noise and Put It In The AudioBufferList /////////////////
/////////////////////////////////////////////////////////////////////////////
// create an array to hold our audio
AudioUnitSampleType audioFile[totalFramesInFile*mChannels];
// fill the array with random numbers (white noise)
for (int i = 0;i < totalFramesInFile*mChannels;i++)
{
audioFile[i] = ((AudioUnitSampleType)(rand() % 100))/100.0;
audioFile[i] = audioFile[i]*0.2;
// (yes, I know this noise has a DC offset, bad)
}
// set the AudioBuffer to point to the array containing the noise
outputData.mBuffers[0].mData = &audioFile;

/////////////////////////////////////////////////////////////////////////////
////////////////// Specify The Output Audio File Format /////////////////////
/////////////////////////////////////////////////////////////////////////////

// the client format will describe the output audio file
AudioStreamBasicDescription clientFormat;
// the file type identifier tells the ExtAudioFile API what kind of file we want created
AudioFileTypeID fileType;
// if compress_with_m4a is tru then set up for m4a file format
if (compress_with_m4a)
{
// the file type identifier tells the ExtAudioFile API what kind of file we want created
// this creates a m4a file type
fileType = kAudioFileM4AType;
// Here we specify the M4A format
clientFormat.mSampleRate         = 44100.0;
clientFormat.mFormatID           = kAudioFormatMPEG4AAC;
clientFormat.mFormatFlags        = kMPEG4Object_AAC_Main;
clientFormat.mChannelsPerFrame   = mChannels;
clientFormat.mBytesPerPacket     = 0;
clientFormat.mBytesPerFrame      = 0;
clientFormat.mFramesPerPacket    = 1024;
clientFormat.mBitsPerChannel     = 0;
clientFormat.mReserved           = 0;
}
else // else encode as PCM
{
// this creates a wav file type
fileType = kAudioFileWAVEType;
// This function audiomatically generates the audio format according to certain arguments
FillOutASBDForLPCM(clientFormat,44100.0,mChannels,32,32,true,false,false);
}

/////////////////////////////////////////////////////////////////////////////
///////////////// Specify The Format of Our Audio Samples ///////////////////
/////////////////////////////////////////////////////////////////////////////
// the local format describes the format the samples we will give to the ExtAudioFile API
AudioStreamBasicDescription localFormat;
FillOutASBDForLPCM (localFormat,44100.0,mChannels,32,32,true,false,false);

/////////////////////////////////////////////////////////////////////////////
///////////////// Create the Audio File and Open It /////////////////////////
/////////////////////////////////////////////////////////////////////////////
// create the audio file reference
ExtAudioFileRef audiofileRef;
// create a fileURL from our path
CFURLRef fileURL = CFURLCreateWithFileSystemPath(kCFAllocatorDefault,fPath,kCFURLPOSIXPathStyle,false);
// open the file for writing
err = ExtAudioFileCreateWithURL((CFURLRef)fileURL, fileType, &clientFormat, NULL, kAudioFileFlags_EraseFile, &audiofileRef);
if (err != noErr)
{
cout << "Problem when creating audio file: " << err << "n";
}

/////////////////////////////////////////////////////////////////////////////
///// Tell the ExtAudioFile API what format we'll be sending samples in /////
/////////////////////////////////////////////////////////////////////////////
// Tell the ExtAudioFile API what format we'll be sending samples in 
err = ExtAudioFileSetProperty(audiofileRef, kExtAudioFileProperty_ClientDataFormat, sizeof(localFormat), &localFormat);
if (err != noErr)
{
cout << "Problem setting audio format: " << err << "n";
}
/////////////////////////////////////////////////////////////////////////////
///////// Write the Contents of the AudioBufferList to the AudioFile ////////
/////////////////////////////////////////////////////////////////////////////
UInt32 rFrames = (UInt32)totalFramesInFile;
// write the data
err = ExtAudioFileWrite(audiofileRef, rFrames, &outputData);
if (err != noErr)
{
cout << "Problem writing audio file: " << err << "n";
}

/////////////////////////////////////////////////////////////////////////////
////////////// Close the Audio File and Get Rid Of The Reference ////////////
/////////////////////////////////////////////////////////////////////////////
// close the file
ExtAudioFileDispose(audiofileRef);

NSLog(@"Done!");
}

不要忘记导入AudioToolbox框架并包含头文件：

#import <AudioToolbox/AudioToolbox.h>