Frank,
Here's the error file generated by totem after I entered 'totem /dev/cdrom' and hit the movie's 'PLAY' button on the screen.
julianloui
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libdvdread: Attempting to use device /dev/sr0 mounted on /media/jul/NEVER_AGAIN for CSS authentication
libdvdnav: Using dvdnav version 4.2.1
libdvdread: Attempting to use device /dev/sr0 mounted on /media/jul/NEVER_AGAIN for CSS authentication
libdvdnav: Can't read name block. Probably not a DVD-ROM device.
libdvdnav: Unable to find map file '/home/jul/.dvdnav/.map'
libdvdnav: DVD disk reports itself with Region mask 0x00fe0000. Regions: 1
libdvdread: Attempting to retrieve all CSS keys
libdvdread: This can take a _long_ time, please be patient
libdvdread: Get key for /VIDEO_TS/VIDEO_TS.VOB at 0x00000129
libdvdread: Elapsed time 0
libdvdread: Get key for /VIDEO_TS/VTS_01_0.VOB at 0x00000447
libdvdread: Elapsed time 0
libdvdread: Get key for /VIDEO_TS/VTS_01_1.VOB at 0x00000731
libdvdread: Elapsed time 0
libdvdread: Get key for /VIDEO_TS/VTS_02_0.VOB at 0x001fee1b
libdvdread: Elapsed time 0
libdvdread: Get key for /VIDEO_TS/VTS_02_1.VOB at 0x001fefc1
libdvdread: Elapsed time 0
libdvdread: Get key for /VIDEO_TS/VTS_03_1.VOB at 0x002016b7
libdvdread: Elapsed time 0
libdvdread: Found 3 VTS's
libdvdread: Elapsed time 0
(totem:2275): Gtk-WARNING **: Calling Inhibit failed: GDBus.Error
rg.freedesktop.DBus.Error.ServiceUnknown: The name org.gnome.SessionManager was not provided by any .service files