Definition(en): Multimedia Viewer Book is a format developed by Microsoft and used by programs such as Encarta to provide interactive, browsable multimedia. The format is very similar to the Microsoft Help .hlp format fmt/474, and a decompiler for the file format, helpdeco is available under a GNU license: https://github.com/pmachapman/helpdeco. The .hlp format this is based on was deprecated with Windows Vista.