Making Your Clips Offline In Final Cut Pro
You can purposely sever the connection between clips in your project and their associated media files on disk for the sake of Offline-Online editing. Make your clips offline so you can delete and recapture the media files at a higher data rate.

Making Clips Offline
1 Within the Browser, select the sequence or clip you want to take offline.
2 Go to Modify > Make offline.
3 Make a selection in the Make Offline dialog box, then choose OK. Your options here are to Leave Them on the Disk (clips are disconnected but still left on disk), Move Them to the Trash (Clips are disconnected and the media files are moved to the trash), and Delete Them from the Disk (clips are disconnected and ,you guessed it, deleted from the disk).
Some tips on managing media in Final Cut Pro.
