Totally bemused now
I rip the DVD to the hard disk, removing all menus, encryption and region coding. It works in all the media players.
I write it to a DVD - still no menus, encryption or region coding. It plays video in Totem but no sound. It doesn't play at all in other media players.
I think I'll give the KDE version a try. I can't see why it'd be any different but I have another hard drive I could use anyway.