I've downloaded Apple's sample code AVFoundationExporter (available from the Apple dev site). The title of the project is "AVFoundationExporter: Exporting and Transcoding Movies", but I'm trying to use it to change an AIFF file to an AAC (M4A) file.
On the desktop, I have a file "testfile.aiff". I invoke it with the command...
AVFoundationExporter "/Users/rbell/Desktop/testfile.aiff" "/Users/rbell/Desktop/testfile.m4a" -preset AVAssetExportPresetAppleM4A -f public.mpeg-4-audio"
(or just [AVFoundationExporter "/Users/rbell/Desktop/testfile.aiff" "/Users/rbell/Desktop/testfile.m4a"])
... I do indeed get a file called "testfile.m4a" on my desktop. And I can indeed play it using Finder's spacebar preview, or using QuickTime.
However, I cannot open it with or import it into iTunes. It simply won't go. I can open the .aiff file just fine, and it plays happily. But when I try to force the .m4a file to "Open in... iTunes", iTunes opens and nothing happens. The .m4a file does not appear in iTunes anywhere.
I tried changing the line
var destinationFileType = AVFileTypeQuickTimeMovie
to
var destinationFileType = AVFileTypeAppleM4A
And it now fails with
error: Operation Stopped: The operation is not supported for this media.. Program ended with exit code: 1
I've fiddled a lot of settings, and nothing seems to work. The -inject-metadata flag doesn't make any difference. Neither does using a -preset. -fileType com.apple.m4a-audio doesn't help. The strange thing is that I really do get the file I want. It just doesn't work properly. If I open my "testfile.m4a" file in QuickTime and export it again, then I end up with an .m4a file with a different bitrate, but this one does open in iTunes.
The file type public.mpeg-4-audio (from kUTTypeMPEG4Audio?) is wrong. You need com.apple.m4a-audio (which corresponds to AVFileTypeAppleM4A).
Don't forget to remove the existing m4a file first!
So your command should be
rm -f out.m4a # AVFoundation doesn't like overwriting existing files.
AVFoundationExporter in.aiff out.m4a -preset AVAssetExportPresetAppleM4A -f public.mpeg-4-audio