To play a DVD on Ubuntu 16.04, you will need to install the Libdvdcss library to enable encrypted DVD playback. This is very simple.
Firstly, download the required library: https://download.videolan.org/libdvdcss/1.2.12/libdvdcss-1.2.12.tar.bz2.
Then move to the Downloads directory and extract the tarball.
[email protected]:~$ tar -xvf libdvdcss-1.2.12.tar.bz2
Then move to the directory to compile the code.
[email protected]:~$ cd libdvdcss-1.2.12/
Then run the configuration script.
[email protected]:~/libdvdcss-1.2.12$ ./configure --prefix=/usr/local
Once completed with no errors, compile the code.
[email protected]:~/libdvdcss-1.2.12$ make
Then install the compiled libraries.
[email protected]:~/libdvdcss-1.2.12$ sudo make install
Once this is completed, open a DVD in Smplayer and it should open with no errors. This is what I did on Ubuntu to play a DVD as this was easier than getting the Videos application to play a DVD.