QuizXpress installs an open source CODEC pack named LAV CODEC pack that is available here: https://github.com/Nevcairiel/LAVFilters/releases. It has support for many of the commonly used multimedia formats.
However these CODEC's are shared between applications on Windows and sometimes installing another program messes up the CODEC's used in QuizXpress and you will receive a message like: "System.Exception: Unable to connect audio renderer to source." or it could also be a message like: "System.Exception: Unable to perform first rendering".
You can easily fix this by reinstalling the CODEC pack by downloading and installing the latest LAV CODEC pack version from here: https://github.com/Nevcairiel/LAVFilters/releases