I don't think either of those subscription services are unicorns or making billionaires. If anything I'm happy to see indie developers able to maintain a decent income making useful (but often niche) tools that other people can use. Of all the SaaS services I pay for, it's one like these that I'm the least apprehensive spending money on.

Video codecs are hard. PDFs are a labyrinth of a file format with traps everywhere. I bet whatever open source equivalent you'd find of these services either require some serious additional tooling to get what you want or are too outdated to be useful anymore because the maintainer moved on from the project.