Your package mkvtoolnix failed to build from source in current rawhide. https://koji.fedoraproject.org/koji/taskinfo?taskID=17738846 For details on mass rebuild see https://fedoraproject.org/wiki/Fedora_26_Mass_Rebuild
Created attachment 1253175 [details] build.log
Created attachment 1253176 [details] root.log
Created attachment 1253177 [details] state.log
Not really FTBFS. It just needed to be rebuilt after libebml due to changes in symbol mangling. Simple rebuild succeeded: https://koji.fedoraproject.org/koji/taskinfo?taskID=17968645 .