This started happening with some change to Qt, maybe by... 5.12? where having "phonon4qt5" in the QT += line stopped generating the Makefile correctly.
The workaround, assuming they don't re-enable that behavior in Qt, is to add the line: LIBS += -lphonon4qt5 somewhere in Auralquiz.pro; right after the other LIBS line, or at the end, would work. -- Development blog: https://jancoding.wordpress.com