Captions/subtitles are not automatically "on" when you export your final edit from FCPX. You could use our latest export option, FCPXML Titles, which will be "on" in the exported file. Or to use FCPXML Captions and have them burn in, follow the instructions below.
The option to export your FCPX projects with burnt-in subtitles became available form FCPX 10.4.4. Here's how to take advantage of this feature.
After transcribing your project in Simon Says, export to Captions and import that into your FCPX project.
Then follow the steps below:
Click Export in the file and choose the Roles tab
Click on the Captions icon under Video Track
Choose Burn in captions from the popup and select your subtitle
Your file is now exported with burnt-in subtitles
Instructions and images, with thanks, from the Idustrial Revolution blog
Related Help Articles:
Auto-sync timecode and frame rate
Best Practices for importing Multicam and Sync clips with the SS FCP X Extension
Can I translate my subtitles within the FCP Extension?
Features of the Simon Says Mac app (a visual guide)
How can I use the transcript editor?
How to caption YouTube videos
How to import into Final Cut Pro X
How-to: Caption & Title FCP Projects
How-to: getting started with the FCP X Extension (video)
Optimizing your FCP X Ranges XML
Supported Imports (FCP X Ext/Mac app)
Visual Subtitle Editor