When Apple added captions to FCPX, the most regular question about them posted on forums was ‘How do I burn them in on export?' You couldn't then, but now you can with Caption Burner, a new plugin from FxFactory.
The implementation of captions in Final Cut Pro X follows Apple's normal path of making a dull and tedious job into one that can be completed quickly and efficiently. A lot of time goes into the design of the GUI and workflow. Take a look at Jason's comments below.
After Adobe Premiere - Captioning in FCP X is like stumbling out of a Djinn infested sandstorm into a palm fringed oasis of mineral water. No. Really. #FCPX— Jason Cumming (@BK2K) July 31, 2018
But there is one feature that is missing and the question of how to burn the captions in on export seems to be regularly posted on social media.
Now Caption Burner, a $99 plugin from Fxfactory has solved that problem. (Usual price $129)
Caption Burner lets you import captions from various formats, customize the appearance through an intuitive UI and then burn them into your video. Caption Burner is super fast as it uses Apple’s Metal graphics acceleration. The plugin lets you work with multiple languages simultaneously, select the language to be burned into the video frame via a simple menu selection.
Supported Formats for captions and subtitles: iTunes Timed Text (iTT), WebVTT (VTT), SubRip (SRT), SubViewer (SUB), Adobe Encore Script and Adobe Premiere Pro Markers (CSV).
Now, you could say that Apple should have provided this feature from the start, but it is good to see a third party addressing the problem quickly.
Also have a look at Caption Converter an app which you can use to convert, edit and translate captions and subtitles of various formats.