My 4K videos stuttered in VLC until I turned off one setting.
So I gave up trying to track down codecs for Quicktime and just accepted that I will be using VLC to play my video files. Well I mount my network share that contains my video files (Windows machine) ...
I morphed this thread into a new question while searching for an app that will easily let me sort organize and search thousands of pictures AND video clips. iPhoto sort of works... but the emphasis is ...