AVMutableMetadataItem.swift

struct Video {
  
  let title: String
  let description: String?
  let category: String
  let thumbnailUrl: URL?
  let …
    
}

fileprivate extension Player {
  
  // MARK: External metadata
  
  func metadata(fromVideo video: Video, completion: @escaping (_ items: [AVMetadataItem]) -> Void) {
    var items = stringItems(fromVideo: video)
    if let url = video.thumbnailUrl {
      metadataArtworkItem(url) { item in
        defer {
          completion(items)
        }
        guard let item = item else { return }
        items.append(item)
      }
    } else {
      completion(items)
    }
  }
  
  func stringItems(fromVideo video: Video) -> [AVMetadataItem] {
    var allItems: [AVMetadataItem] = []
    allItems.append(metadataItem(AVMetadataCommonIdentifierTitle, value: video.title))
    allItems.append(metadataItem(AVMetadataCommonIdentifierDescription, value: video.description?))
    allItems.append(metadataItem(AVMetadataIdentifierQuickTimeMetadataGenre, value: video.category))
    return allItems
  }
  
  func metadataItem(_ identifier: String, value: String?) -> AVMetadataItem {
    let item = AVMutableMetadataItem()
    item.identifier = identifier
    if let value = value {
      item.value = value as NSString
    }
    item.extendedLanguageTag = "und"
    return item.copy() as! AVMetadataItem
  }
  
  func metadataArtworkItem(_ imageUrl: URL, completion: @escaping (_ item: AVMetadataItem?) -> Void) {
    let task = URLSession.shared.dataTask(with: imageUrl) { data, _, error in
      guard let data = data, let image = UIImage(data: data), error == nil else {
        completion(nil)
        return
      }
      let item = AVMutableMetadataItem()
      if let data = UIImagePNGRepresentation(image) {
        item.value = data as NSData
      }
      item.dataType = kCMMetadataBaseDataType_PNG as String
      item.identifier = AVMetadataCommonIdentifierArtwork
      item.extendedLanguageTag = "und"
      completion(item as AVMetadataItem)
    }
    task.resume()
  }

}