How to add html elements to a video online

I need to be able to edit a video with online technologies (Javascript or with some Backend code) and overlay on the original video whatever html elements (maybe even animated elements with css) and download the new video edited.

What is the best way to do it?

I've read about CCapture.js that captures videos from a canvas, but I can't get it to work and I'm not sure it's what I'm looking for. I've read about some FFMPEG plugins to make it work on the server and use it with some backend languages but I don't know if it would get the work done as I need it.

For clarity, you know how Instagram can edit your video after you take it adding text or images? I need to be able to edit a video like that, adding html elements on it.

Thanks in advance for helping.