Editing metatags of mp4 / m4a files

Question

I want to edit the Title and the Author tag on a mp4 / m4a file with ObjC for iOS.

Is this possible?

Answer 1

There's probably more than one way, but AVAssetExportSession is simple and works.

N.B. This creates a new file. AVFoundation doesn't really do in place modifications.

#import <AVFoundation/AVFoundation.h>
#import <CoreMedia/CoreMedia.h>

// ...

NSURL *outputURL = [NSURL fileURLWithPath:[NSString stringWithFormat:@"%@/output.m4a", [NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES) firstObject]]];
[[NSFileManager defaultManager] removeItemAtURL:outputURL error:nil];

NSURL *inputURL = [[NSBundle mainBundle] URLForResource:@"foo" withExtension:@"m4a"];
AVAsset *asset = [AVAsset assetWithURL:inputURL];

AVAssetExportSession *session = [[AVAssetExportSession alloc] initWithAsset:asset presetName:AVAssetExportPresetPassthrough];
session.outputURL = outputURL;
session.outputFileType = AVFileTypeAppleM4A;

AVMutableMetadataItem *metaTitle = [[AVMutableMetadataItem alloc] init];

metaTitle.identifier = AVMetadataCommonIdentifierTitle;                     // more in AVMetadataIdentifiers.h
metaTitle.dataType = (__bridge NSString *)kCMMetadataBaseDataType_UTF8;     // more in CoreMedia/CMMetadata.h
metaTitle.value = @"Choon!";

AVMutableMetadataItem *metaArtist = [[AVMutableMetadataItem alloc] init];
metaArtist.identifier = AVMetadataCommonIdentifierArtist;
metaArtist.dataType = (__bridge NSString *)kCMMetadataBaseDataType_UTF8;
metaArtist.value = @"Me, of course";

session.metadata = @[metaTitle, metaArtist];

[session exportAsynchronouslyWithCompletionHandler:^{
    if (session.status == AVAssetExportSessionStatusCompleted) {
        // hurray
    }
}];

This example is for m4a files, you'll need to change the file extensions to mp4 and outputFileType to AVFileTypeMPEG4.