Subtitles cannot be customized

@OmicronAG,

I'll add a bit to the response.

There are 2 ways to change the format. We often recommend right-clicking the caption track in the track header area, pick "track settings," and change to "subtitle."

However, that will keep the caption creation options used to make the captions. For 708 captions that is a maximum of 42 characters per line. Another alternative is to create a new caption track from the transcript. If you pick Subtitle there, you can increase the characters per line to 72.

Stan

Thank you for your feedback.

It looks like you create the subtitles in the 708 format which does not support additional styling as it is meant to be used for embedded captions that are displayed in a very specific way by the player devices.
If you want to be able to fully style your subtitles you need to select the "Subtitle" caption format which allows for a much wider selection of styles to be applied.

Best regards,
 Alexander