Forced subtitles: subtitles that disc player should always play in same language as active audio language.
  Forced or 'Forced-only' subtitles are mostly used to translate text burnt in original movie.
ISO image file: ISO file (extension .iso) is an image of every bit of a physical disc (CD, DVD, Blu-ray) stored in a unique file. ISO images are convenient for data and movie backup or for disc image library to share in local network from a file server.
  On Windows 8, just double-click an ISO file and the image is mounted as a virtual drive.
  On other Windows version (XP, Vista, 7), Microsoft offers a free utility: Virtual CD-ROM Control Panel.