Why not use youtube-dl? ( https://github.com/ytdl-org/youtube-dl )
The "po" youtube URL modification is clever, but I don't know how long you will be able to keep this running.
whether this is a good or a bad converter API for youtube I think this is an unfair usage of github. I was interested in seeing the source code for such a product (github is a development platform). Instead your github project is just a page to describe a product hosted somewhere else. Not good.