QuickTime-Fixer
Mountain Lion QuickTime supports third party codecs. This means you can install Perian and play all sorts of videos! I wanted to use this version of QuickTime on Mavericks!
I got it 95% working just by relinking frameworks via install_name_tool, but for the last 5%, I had to inject the code in this repo. It's heavily commented, so feel free to take a look: https://github.com/Wowfunhappy/QuickTime-Fixer/blob/master/QuickTimeFixer/main.m
Or, if you're running Mac OS X 10.9 Mavericks, just download the app from: https://jonathanalland.com/old-osx-projects.html
Note, while this is designed to replace the system QuickTime, please do make sure to keep a backup of the original!
P.S. I also made this version of Quicktime save and restore your current position in a file. If you don't like this for some reason, delete userFileClosedScript.scpt and userFileOpenedScript.scpt from Contents/Resources/. Or, feel free to edit those scripts to do something else when you open and close a file!