iOS audio manipulation - play local .caf file backwards

Question

I\'m wanting to load a local .caf audio file and reverse the audio (play it backwards). I\'ve gathered that I basically need to flip an array of buffer data from posts like

Answer 1

I have worked on a sample app, which records what user says and plays them backwards. I have used CoreAudio to achieve this. Link to app code.

As each sample is 16-bits in size(2 bytes)(mono channel). You can load each sample at a time by copying it into a different buffer by starting at the end of the recording and reading backwards. When you get to the start of the data you have reversed the data and playing will be reversed.

// set up output file
AudioFileID outputAudioFile;

AudioStreamBasicDescription myPCMFormat;
myPCMFormat.mSampleRate = 16000.00;
myPCMFormat.mFormatID = kAudioFormatLinearPCM ;
myPCMFormat.mFormatFlags =  kAudioFormatFlagsCanonical; 
myPCMFormat.mChannelsPerFrame = 1;
myPCMFormat.mFramesPerPacket = 1;
myPCMFormat.mBitsPerChannel = 16;
myPCMFormat.mBytesPerPacket = 2;
myPCMFormat.mBytesPerFrame = 2;


AudioFileCreateWithURL((__bridge CFURLRef)self.flippedAudioUrl,
                   kAudioFileCAFType,
                   &myPCMFormat,
                   kAudioFileFlags_EraseFile,
                   &outputAudioFile);
// set up input file
AudioFileID inputAudioFile;
OSStatus theErr = noErr;
UInt64 fileDataSize = 0;

AudioStreamBasicDescription theFileFormat;
UInt32 thePropertySize = sizeof(theFileFormat);

theErr = AudioFileOpenURL((__bridge CFURLRef)self.recordedAudioUrl,kAudioFileReadPermission, 0, &inputAudioFile);

thePropertySize = sizeof(fileDataSize);
theErr = AudioFileGetProperty(inputAudioFile, kAudioFilePropertyAudioDataByteCount, &thePropertySize, &fileDataSize);

UInt32 dataSize = fileDataSize;
void* theData = malloc(dataSize);

//Read data into buffer
UInt32 readPoint  = dataSize;
UInt32 writePoint = 0;
while( readPoint > 0 )
{
   UInt32 bytesToRead = 2;

AudioFileReadBytes( inputAudioFile, false, readPoint, &bytesToRead, theData );
AudioFileWriteBytes( outputAudioFile, false, writePoint, &bytesToRead, theData );

writePoint += 2;
readPoint -= 2;
}

free(theData);
AudioFileClose(inputAudioFile);
AudioFileClose(outputAudioFile);