My GNOME desktop's setup is configured so that DVDs aren't auto-played when inserted. Inserted media aren't auto-mounted either. Instead I'm using the Drivemount applet to mount, open, start play, when I wish so, by using its menus.
However, I've been annoyed for a while by the fact that when I had mounted a DVD's disc, and I started "Play DVD" from drivemount-applet's menu, totem would start, but it wouldn't play the DVD, complaining that "Totem could not play 'dvd://'. The source seems encrypted, and can't be read. Are you trying to play an encrypted DVD without libdvdcss?" :(
It seems that changing the DVD auto-play command in Gnome settings' Removable drives & Media Preferences configuration dialog from 'totem dvd://' to 'totem dvd://%m' helped achieve what I needed.
Now totem is started with something like 'totem dvd:///media/DVD_MOVIE', and plays the film as expected.
This post helped me figure out how to achieve that : http://people.debian.org.tw/~chihchun/2007/06/20/fix-the-vcd-auto-play-command-in-gnome/
