Are the subtitles too small after adding the VTT file? You can change the subtitle font size making it easier to read for viewers.
See Add Subtitles to a Video, if you need help adding subtitles.
To change the font size insert a small line of code to either a new CSS file or add it directly to the Theme.liquid file.
We recommend making a backup before making any changes to your site.
Navigate to Customization > Advanced > Code Editor > Theme.liquid.
Add the code below just before the closing style tag.
Then Save. You should be all set!