I now have another kind of hybrid source. 29.97fps, some sections need tfm().tdecimate(), other sections need QTGMC(), so this would be a hybrid of some parts in 23.976fps and some parts in 59.94fps. Is there some way to achieve this automatically? And if not, what's the best manual way to do it?
EDIT: a better forum search led me to
https://forum.doom9.org/showthread.php?p=1713315 or
https://forum.doom9.org/showthread.php?t=173147, will dig into that.....
EDIT, some time later: Damn, is it really that hard?