AudioFileOpen not opening with read/write permissions - objective-c

Question

I am trying to programmatically optimize AAC files (.m4a) that were created by software other than iTunes or afconvert using AudioFileOptimize().
However, when I attempt to do an AudioFileOpen with read/write permission and it gives me an error. I can only open with read permissions even if I manually set the POSIX permissions to 0666 (r/w for everyone.)
I'm using the AudioFileOpenUrl method described here and get back 'prm?' (kAudioFilePermissionsError).
Here is the code that is throwing the error:
#import <Cocoa/Cocoa.h>
#import <CoreFoundation/CoreFoundation.h>
#import <AudioToolbox/AudioToolbox.h>
#import "CAXException.h"
int main(int argc, const char * argv[])
{
int result = 0;
try {
//optimize the output file:
AudioFileID outfile;
NSURL *outputFileURL = [NSURL fileURLWithPath:#"/DIR/PATH TO.m4a"];
OSStatus err = AudioFileOpenURL((__bridge CFURLRef)outputFileURL, kAudioFileReadWritePermission, 0, &outfile);
XThrowIfError(err, "AudioFileOpenURL");
err = AudioFileOptimize(outfile); //Optimize the file
XThrowIfError(err, "AudioFileOptimize");
err = AudioFileClose(outfile);
XThrowIfError(err, "AudioFileClose");
} catch (CAXException e) {
char str[32];
printf ("CAXException thrown from CoreAudioConverter.mm. : %s, %s\n", e.FormatError(str), e.mOperation);
result = 1;
} catch (...) {
result = 1;
}
return result;
}
This outputs:
CAXException thrown from CoreAudioConverter.mm. : 'prm?', AudioFileOpenURL
If anyone can help, that would be AWESOME!
Side-note, has anyone done any work programmatically adding streaming hints to aac files?
Thanks!

Answer 1

AudioFile Services will not allow Write access to certain files:
There is however a limitation when working with MPEG-4 file types which include; .mp4 (kAudioFileMPEG4Type), .m4a (kAudioFileM4AType), .3g2 (kAudioFile3GP2Type) and .3gp (kAudioFile3GPType).
AudioFile does not currently support writing to existing files of these types.
See:
http://developer.apple.com/library/mac/#qa/qa1676/_index.html