Final cut keeps crashing

Start by deleting preferences, and repeat the procedure whenever the application crashes.

To delete preferences, hold down command and option while starting FCP X and click Delete Preferences.

You will then have to open your library, but none of your content is deleted, rest assured.

If deleting preferences does not fix things, please run the diagnostic tool Etrecheck and post its full report here.

Use the "additional text" button, as the report is too long to paste directly in the message area.

Do you use Chrome? Just saw an article on AppleInsider.com: Chrome causing Final Cut Pro X to slow down, freeze, and crash. Seems to be some proof to it -- tested Handbrake encode of H.264 with an open and idling Chrome browser... there was a 30% hit on the encoding.