A client wants the subtitles out of the way of the video, so they want it underneath the video. We are using vtt files for our captions. Can this be done in CSS? Maybe some settings in the vtt file?
short answer... no.
longer answer... you could parse the vtt and manually display the captions outside the <video> tag, there are a few JS libraries out there to do this (eg Mozilla have a very thorough implementation, though depending on your captions you may be able to get away with something a lot more lightweight)