private function getInvalidMetadata(FileUpload $song) : array
 {
     $invalidMetadata = [];
     $songReader = new \SongReader($song->getTemporaryFile());
     if (!$songReader->getDuration()) {
         $invalidMetadata[] = 'playtime_string';
     }
     if (!$songReader->getAuthor()) {
         $invalidMetadata[] = 'artist';
     }
     if (!$songReader->getTitle()) {
         $invalidMetadata[] = 'title';
     }
     if (!$songReader->getAlbum()) {
         $invalidMetadata[] = 'album';
     }
     return $invalidMetadata;
 }
 public function loadMetadata(\SongReader $songReader)
 {
     $songReader->getTitle() ? $this->title = $songReader->getTitle() : null;
     $songReader->getAuthor() ? $this->artist = $songReader->getAuthor() : null;
     $songReader->getDuration() ? $this->duration = $songReader->getDuration() : null;
 }