Where apps hide your files
iMovie quietly duplicates your footage into a library package, and the copies are what fill the disk.
~/Movies/iMovie Library.imovielibraryA package. Inside: one folder per event, holding Original Media (copies of everything you imported) and Render Files (previews and transcodes iMovie generates while you edit).
Importing copies footage in by default, so every clip exists twice — the original wherever it was, and the library's copy. Render files then add more, often rivalling the originals.
Inside iMovie: File → Delete Rejected Clips, and for finished projects, delete the project and its events from within the app so the database stays consistent.
Render files can be purged per library: select the library in iMovie's sidebar → File → Delete Generated Library Files. They regenerate if needed.
Quit iMovie, copy the .imovielibrary package to the drive (APFS or Mac OS Extended — it will refuse or misbehave on exFAT), then double-click the copied library to open from there. Once verified, delete the internal one.
Original Media inside the package contains your untouched imports — right-click the library → Show Package Contents → the event folder → Original Media. Copy out; do not reorganise in place.
The finished movie is different: File → Share → File exports the actual video. People routinely lose "the video" because it only ever existed as a project — export finished work, every time.
It contains copies of all imported footage plus render files. Deleting generated files and rejected clips reclaims much of it.
Yes, on APFS or Mac OS Extended drives. Copy the package over, open it from there, then remove the internal copy.
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