如何使用音频文件服务获取音频文件的原始数据？

Question

I'm trying to use the Audio File Services from the AudioToolBox framework to get the raw data from a wav file. Specifically, I'm using AudioFileReadBytes() call to get the bytes. Here is the relevant code I have:

NSString *audioFilePath = [[NSString stringWithCString:argv[1]
                                              encoding:NSUTF8StringEncoding]
                           stringByExpandingTildeInPath];          
NSURL *audioURL = [NSURL fileURLWithPath:audioFilePath];               

AudioFileID audioFile;                                               
OSStatus theErr = noErr;
UInt64 fileDataSize = 0;
AudioStreamBasicDescription theFileFormat;
UInt32 thePropertySize = sizeof(theFileFormat);
theErr = AudioFileOpenURL((CFURLRef)audioURL, kAudioFileReadPermission, 0, &audioFile); 

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

//Read data into buffer
UInt32 dataSize = fileDataSize;
void* theData = malloc(dataSize);
if (theData) {
    AudioFileReadBytes(audioFile, false, 0, &dataSize, theData);
            // create an NSData object to hold the buffer data
    NSData* nsdata = [NSData dataWithBytesNoCopy:theData length:dataSize]; //?
}

Now the question is: after I create the NSData object (nsdata), how do I get the numbered values from it (like if I do 'wavread' in Matlab it will give me an array of floats) so that I can manipulate the values(eg to pass through some filter)?

Any input is greatly appreciated!

Answer 1

I'm not sure why you need the NSData object at all.

Using AudioFileGetProperty with kAudioFilePropertyDataFormat, you should be able to determine the type of audio data (eg array of floats) etc, and therefore how to interpret "theData".