/usr/lib/x86_64-linux-gnu/libQt5Multimedia.so is in qtmultimedia5-dev 5.2.1-0ubuntu5.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/lib/x86_64-linux-gnu/libQt5Multimedia.so.5.2.1
/usr/lib/x86_64-linux-gnu/libQt5Multimedia.so.5.2.1