Perian was an indispensable open-source component that let QuickTime Player 7 and earlier versions of QuickTime X play virtually any video format: AVI, MKV, FLV, WMV, DivX, XviD, and many more. It added subtitle support and an enhanced audio matrix.
If you’ve been using macOS since the Snow Leopard or Lion days, you probably remember – “The Swiss Army Knife for QuickTime.”
Here’s a properly structured post for (the now-discontinued Mac video codec pack). I’ve written it as if you’re sharing a retrospective or troubleshooting tip on a forum, blog, or social media. Title: Perian for Mac: A Retrospective & Modern Setup Guide