Caveat: I’m JUST beginning to learn Final Cut Pro X, and these instructions may NOT be the best way to do this
- FIRST, make a copy of the Library folder that holds everything (Library, Media, Events, Projects), and re-name both the Folder and the Library file (don’t want to lose the original 16:9 layout version).
- Open Final Cut Pro X and locate the copied re-named Library: File > Open Library > Other > Locate > Folder > Library file (pick the Library file, not the Folder)
- Window > Project Properties > (Inspector > Modify) > Change Video: “1080p HD 1920×1080” to “Custom: 1080×1080”
- (To keep 16:9 clip with black top/bottom bars): Click on clip > Video Inspector > Spacial Conform > Type > Fit setting
- (To force 16:9 clip to fill the new 1:1 layout, and cut off left/right sides of the 16:9 video) Click on clip > Video Inspector > Spacial Conform > Type > Fill setting
- EXPORT: Share > Master File > Settings > Format: Computer (to get a MP4 file) > Resolution: 1080×1080