Preservica does have the ability to render SRT/WebVTT captioned video, however the caption file(s) and the video file need to be part of the same Multi-Part Asset in Preservica, I’m not sure how easy/possible that is with Starter as it is primarily an advanced functionality.

Preservica doesn’t render mp3 audio with captions, the only way to make that work would be to have your audio in an MP4 file that only had an audio stream.