And again, when watching DVDs does not work on Ubuntu 15.04, you must install the restricted codecs (ubuntu-restricted-extras). After that you must install libdvdcss2 which is not in the repositories (for some strange reason). Even though I installed it in 14.10, after the upgrade it was not installed anymore. You have to run the following command on a terminal:
$ sudo /usr/share/doc/libdvdread4/install-css.sh
This fixed Handbrake for me once again.
Brain/Drain/Pain 