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.css), it's not included in Debian.