Garrels.be

Up to an update performed earlier this year (2011, don't know which update ruined my system), I was able to play (officially acquired!) DVDs. Actually, I never tried more than one: the (belgian) Hopla DVD for my son. Myself, I'm more of a commandline person, so there was no need to experiment.
Then, I bought a UK DVD, Meg and Mog, which did not play on my system. I first tried with the standard Ubuntu movie player, which is Totem with gstreamer. It said:

Totem:

"Totem was not able to play the disc: no reason"

"Movie player could not read from resource"

An access problem, user permissions and such? No, because I was still able to play my first DVD.

After Googling a bit, it seemed that I did not have the necessary codecs installed. So I installed them (w32codecs, and some other stuff from medibuntu): same problem. Googled some more, try with VLC, say some people:

"VLC could not read the file"

The files, btw, were simple mpeg2 files. Should not pose a problem, or should it?

The single most useful advise that I found is this: you're doing it wrong. In VLC, you should use the interface and say "Play disc" instead of using the file manager and right-clicking to open the individual .VOB files. I suppose everybody else knows this, and that it is in the man page, but for me, it cost me another hour of my life, not being a gui-person.

So the thingie really having to do with the update was that the first user who logged into the system got the monopoly of the sound device. After switching to another user, before, I also had this problem, but it could be worked around by opening the sound preferences and muting and unmuting the device for output. Now, this was no use. All users belong to the audio group, the permissions on the audio devices were not changed, but no use. Because the users who logged in after the first one also could not access the CD and DVD drives, I also checked the advanced user settings to verify that user privileges were ok. In User Privileges I gave all users permission to "Use audio devices". Turns out this was the problem. In the new Ubuntu (lucid) this means "use audio devices exclusively". Just unchecking this user privilege for all users solved my problem, as access to the actual audio device is ruled by some ACLs elsewhere. Another hour of my life gone... At least I hope these explications can be useful for others, as I went through heaps of nonsense that had nothing to do with my actual problem.