This old issue is only reported by CrossOver 19 and older. See the current Missing GStreamer 1.0 Base plugins page for more details.
See the current Missing GStreamer 1.0 Base plugins page for how to install this set of GStreamer plugins.
However note that because of a bug in CrossOver 19 and older it may not recognize the plugins on Fedora, openSUSE, and the related distributions. The workaround is to delete $HOME/.cache/gstreamer-1.0/registry.i686.bin and immediately run the Windows application that needs these plugins.