QLibraryInfo::location(QLibraryInfo::PluginsPath) only returns the
plugin path for the Qt installation.  However, the encoder plugins
may have been installed elsewhere and located using the QT_PLUGIN_PATH
environment variable, in addition to as the Qt installation location.
Any plugins located elsewhere will not be found, resulting in an
assert in encoderFromExtension() when the AudioCDProtocol is constructed.

Look for plugins in all possible locations returned by
QCoreApplication::libraryPaths() instead.