libdvdread provides the functionality that is required to access many DVDs. It parses IFO files, reads NAV-blocks, and performs CSS authentication and descrambling. . libdvdread probes for libdvdcss at runtime and if found, will use it to decrypt sections of the DVD as necessary. libdvdcss needs to be installed from third-party repositories (see README.Debian), it's not included in Debian.