Keeping the folder from filling up

Delete by age, by total size, or both. Mark clips Keep to protect them.

Two independent limits, either of which can be switched off:

Age — anything older than the set number of days is removed.
Total size — when the folder exceeds the limit, the oldest clips are deleted until it's back under.

A clip currently being written is never deleted, however tight the limits are.

To protect something permanently, tag it "Keep" in the Finder or make it read-only. Protected clips still count toward the size total but are never removed — which does mean a folder full of protected clips can exceed the limit, and nothing can be done about that automatically.