Why no artwork in iTunesLibrary Framework?

Maybe this can help someone in the future as I am sure you've already worked this out after 5 years.

I use this to get album artwork that is embedded in the MP3 file (all my music in my library is MP3 music).

      let playerItem = AVPlayerItem(url: mp3URL)
      let mp3Details = playerItem.asset.metadata
      for item in mp3Details {
        guard let key = item.key?.description, let value = item.value else {
          continue
        }
        /*
         TPE1 = Album artist
         TPE2 = Artist
         USLT = Lyrics
         COMM = Comments
         TCON = Genre
         TRCK = Track of tracks
         TCOM = Composer
         TSSE = Encoder
         TPOS = Disk of Disks
         TDRC = Year released
         TALB = Album Name
         TBPM = Beats per minute
         */
        switch key {
        case "***2": mp3Info["title"] = value as? String ?? nil
        case "TPE1": mp3Info["artist"] = value as? String ?? nil
        case "APIC" where value is NSData : mp3Info["artwork"] = NSImage(data: (value as! NSData) as Data) ?? nil
        case "TALB": mp3Info["album"] = value as? String ?? nil
        case "USLT": mp3Info["lyrics"] = value as? String ?? nil
        case "TBPM": mp3Info["bpm"] = value as? Int ?? nil
        default: continue
        }
      }

Of course, this will probably not work on downloaded artwork, since that is an Apple product/service. But if you have MP3 files and you add artwork manually, like I do for my music, then this should work for retrieval.