.FCPBUNDLE File Extension
What is an FCPBUNDLE file?
Library created and used by Final Cut Pro X (FCPX), a professional video editor; contains files that make up a library in FCPX, which includes a .FLEXOLIBRARY file, .FCPEVENT files describing events, and a .PLIST file that contains backup metadata.
The FCPBUNDLE file is located in the following directory:
MacHD/Library/Users/[username]/Movies/Final Cut Backups