Readme says it can be run standalone. That might still be true, but don't count on it. A year ago I migrated to python 3 and added support for playlists that I am not sure got exposed. None of that matters for this project.
It is meant to be used as part of a bigger system that iterates over the list of videos/metadata and has a place to store the resulting URL, or at least mark each one as being uploaded:
https://github.com/CarlFK/veyepar/blob/master/dj/scripts/post_yt.py#L162-L212
I wold be delighted if someone would try to call lib/youtube_v3_uploader.py from some other data source. It would prove (or disprove) isolation of... concerns? something.