Author here! You need QuickTime 10.2 (Mountain Lion) or older to use third party codecs like Perian or my updated FFusion. I managed to patch QuickTime 10.2 to

Author here! You need QuickTime 10.2 (Mountain Lion) or older to use third party codecs like Perian or my updated FFusion. I managed to patch QuickTime 10.2 to work on Mavericks (on the website), but I would not expect it to work on High Sierra. You can use QuickTime 7 on High Sierra with third party codecs. I am not a fan of QuickTime 7.