Detailed steps which must be run in the Debian 8 template VM.
A good idea might be to clone the existing Debian 8 template and create an own debian-8-multimedia template from whoch you can then create an App-VM.
You need to make sure that you allow networking to the internet during installation, as you need to download some data which are not from the default repositories.
To play DVDs within Qubes I have used my new multimedia App VM (which can also play Spotify and Netflix, see post from yesterday).
The multimedia App-VM is based on the Debian 8 Template in Qubes 3.2
Some suggested to install the whole desktop within the Debian Image, I don't want to install everything but only the stuff, that is really needed.
As such I have looked at the Debian documentation
1) Launch Debian 8 Template VM and install the Qubes Proxy Tools, so that you can pass your (external?) DVD-Drive via sys-usb to the multimedia App-VM. Strangely the qubes-usb-proxy seems to be installed within the fedora template but not in the debian template.
In Debian Template VM:
sudo apt-get install qubes-usb-proxy
2) Install libdbdread4 from the default repositories:
In Debian Template VM:
apt-get install libdvdread4
3) Install libdvdcss for the decryption of CSS protected-DVDs.
Because of license restrictions in various countries this can't be done from the Debian repositories but needs to be installed manually.
(not that hard :-)).
Download the packaged .deb from: http://www.deb-multimedia.org/dists/stable/main/binary-amd64/package/libdvdcss2