Retrieving the key name on AVMetadataItem for an AVAsset in iOS - iphone

Question

I am trying to identify the different metadata items on a video on the iPad. So far I was able to successfully use the AVAsset libraries to find the file, and generate an array of AVMetadataItems using metadataForFormat:. Only iTunes and Quicktime User data formats were found in the file. The issue is now that I have that information, I have no way of identifying what is what. I intended to load a dictionary with the information, indexed by the metadata key, but using the key property of AVMetadataItem appears not to work correctly as if returns a number (debugger says its an NSCFNumber). Here is some sample code of what I am doing:
ALAssetRepresentation *representation = [[valAsset defaultRepresentation] retain];
NSURL *url = [representation url];
AVURLAsset *aAsset = [[AVURLAsset URLAssetWithURL:url options:nil] retain];
metaDataDict = [[NSMutableDictionary dictionary] retain];
NSArray *fmtmetadata = [aAsset metadataForFormat:#"com.apple.itunes"];
for (AVMetadataItem* meta in fmtmetadata)
{
[metaDataDict setObject:[meta stringValue]
forKey:[meta key]];
NSLog(#"metadata: key = %#", [meta key]);
}
This yields the following output in the debugger console:
metadata: key = -1452383891
metadata: key = -1452841618
metadata: key = 1684370275
metadata: key = 1818518899
metadata: key = 1937009003
metadata: key = -1453101708
Incidentally, changing the NSLog line to read:
NSLog(#"metadata: %#", meta);
gives us output like:
metadata: keySpace=itsk, key=desc, commonKey=(null), locale=(null), value=This is the Description of the Video, time={INVALID}, duration={INVALID}, extras={
dataType = 1;
}
Any help is greatly appreciated!

Answer 1

Looks like these keys are encoded ID3 tags:
1684370275 = 0x64657363 = {'d', 'e', 's', 'c'}
1818518899 = 0x6C646573 = {'l', 'd', 'e', 's'}
1937009003 = 0x7374696B = {'s', 't', 'i', 'k'}
etc.

Answer 2

You can use following extensions:
extension AVMetadataItem {
var keyString: String {
if key is NSString { return key as! String}
else if key is NSNumber {
var keyValue = (key as? NSNumber)?.uint32Value ?? 0
keyValue = CFSwapInt32BigToHost(keyValue)
let array = withUnsafeBytes(of: &keyValue) { Array($0) }
let string = String(decoding: array, as: UTF8.self)
return String(string.map {$0 == "�" ? "#" : $0 })
} else {
return "Unknown"
}
}
}
It can return strings like this:
keyString
Description
#alb
Album
aART
Album Artist
#ART
Artist
#gen
Gener
#nam
Title
#cmt
Comment
To use:
let albumMetaData: [AVMetadataItem] = AVMetadataItem.metadataItems(from: asset.metadata, filteredByIdentifier: .iTunesMetadataAlbum)
print(albumMetaData.first?.keyString) // #alb
Credit goes to:
Learning AV Foundation: A Hands-on Guide to Mastering the AVFoundation Framework (McCune, Bob)