There's one key in Final Cut Pro that'll make your editing life so much easier, especially if you're just starting out or switching over from something like Premiere. It's the tilde key, that symbol that looks like a flowing wave. Quick heads up: if you're not on a US keyboard you might not have it, but stick around and I'll show you how to assign what it does to any key you want.
It overrides the magnetic timeline
Take a clip on your primary storyline with some sound effects and voiceover attached, plus B-roll and titles over the top. Because of Final Cut's magnetic timeline, if you try to delete just that primary clip, it drags everything attached to it along with it. The magnetic timeline is an awesome feature and incredibly useful, just not in a moment like this. So instead, hold the tilde key (you'll get this weird little orange icon) and then press delete. The attached clips stay exactly where they are on the timeline.
It works for slips and moves too
This key does more than delete. Say you want a slip edit: press T for the trim tool to change the start and end points of a clip, but when you scroll through it, everything moves with it. Hold tilde, scroll, and nothing else budges. Same when you want to move a clip but keep the B-roll and audio in place, without the key it's a no-go, but hold tilde and you take full control, overriding the magnetic timeline.
Don't have the key? Reassign it
If you don't see the tilde on your keyboard, here's how to map it. Press Option Command K, duplicate the default keyboard if you haven't already, and search Override Connections. You'll see it's assigned to the grave key right next to the tilde. Select it, press whatever key you want (say the = key), and hit reassign, just don't pick a key you actually need for something else. Then delete the default and hit save.
Edit faster with my custom shortcuts
Grab my free Final Cut Pro keyboard shortcuts cheat sheet. It's the exact custom setup I use to edit every video, and it'll shave time off every session.
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