Can't get key value as String from metadata - swift3

Question

I'm grabbing metadata from an MPMediaItem like this:
let url = item.value(forProperty:MPMediaItemPropertyAssetURL) as? NSURL
let asset = AVURLAsset(url: url! as URL, options: nil)
let metaArray = asset.metadata
for metadata in metaArray{
print("-----metadata:\(metadata)")
print("-----metadata.key:\(String(describing: metadata.key))")
}
However, when I get a block of metadata printed the "key" is printed as a numeric value instead of "pcst" as shown in the printout:
-----metadata:<AVMetadataItem: 0x1740153f0, identifier=itsk/pcst, keySpace=itsk, key class = __NSCFNumber, key=pcst, commonKey=(null), extendedLanguageTag=(null), dataType=com.apple.metadata.datatype.int8, time={INVALID}, duration={INVALID}, startDate=(null), extras={
dataLength = 1;
dataType = 21;
dataTypeNamespace = "com.apple.itunes";
}, value=1>
-----metadata.key:Optional(1885565812)
This is happening for all of the metadata/keys (there are 29 in this particular media item).
Also note that this line of code:
let realString = NSString(string: metadata.key! as! String)
causes this error:
Could not cast value of type '__NSCFNumber' (0x1b80dcdf0) to 'NSString' (0x1b80edae8).
How can I get the string value for the key ("pcst") ?

Answer 1

May be what you are looking for is identifier property of AVMetadataItem.
for metadata in metaArray{
print(metadata.identifier ?? "DefaultValue")
}

Answer 2

In case others want to see the code I'm using:
func returnKeyString(_ inVal: String)->String{
// expecting the metadata for "identifier" as input - returns key value
// eg "itsk/ldes" -> "ldes"
// or "id3/%00WFD" etc. -> "wfd"
var sFinal:String = ""
if (inVal.contains("/")){
sFinal = (inVal.components(separatedBy: "/")[1])
}
if sFinal.contains("%"){
sFinal = sFinal.components(separatedBy: "%")[1]
let index1 = sFinal.index(sFinal.startIndex, offsetBy: 2)
sFinal = sFinal.substring(from: index1)
}
return sFinal.lowercased()
}