Configuring Subtitles

I'm working on a site that requires Section 508 compliance and saw that the latest version of this module (Drupal 8) has support for VTT subtitles. Following the README file, I created a field using the File type and set it up for unlimited entries. I added the mp4 file for the first entry and the VTT file as the 2nd with EN in the description.

"## Subtitle tracks

To add subtitles to your video, upload a VTT file to the file field, or
link to a VTT file when using a Link field. Enter the language name or
two-letter code in the description field. Use the English or local language
name."

Unfortunately, I am still not seeing subtitles and have not been able to track down any further documentation about how to fix this. Any help would be greatly appreciated.