public override void Read(BoxReader reader)
 {
     using (new SizeChecker(this, reader))
       {
     long startpos = reader.BaseStream.Position;
     base.Read(reader);
     UserType = reader.ReadExtendedBoxType();
     int contentSize = (int)((long)base.Size - (reader.BaseStream.Position - startpos));
     if (contentSize > 0)
     {
       Contents = new byte[contentSize];
       reader.Read(Contents, 0, contentSize);
     }
       }
 }