Some news ! Reinstalled frei0r-plugins and as usually, bad behavior with kdenlive and shotcut. Then I manually removed all plugins that are not thread safe and now, both software are working as expected !! https://github.com/mltframework/mlt/blob/master/src/modules/frei0r/not_thread_safe.txt There's something here: https://github.com/mltframework/mlt/blob/master/src/modules/frei0r/factory.c At this point, untill a proper fix is found, I would split frei0r-plugins in 2 packages. One with all safe plugins and another with all "bad" plugins, so we can avoid them... What do you think ?