Here are a set of tools to try to identify and count the number of movies in the Internet Movie Database it is legal to distribute on the internet, either because they are no longer copyright protected (aka public domain) or because they are licenced using a license allowing such distribution (for example with a Creative Commons license).
At a glance I don’t see indication of specific license that would allow for creating a libre-only dataset, but nonetheless this is an exciting project.
It would be great for improving the accuracy of this measurement, if the various sources added IMDB title ID to their metadata. I have tried to reach the people behind the various sources to ask if they are interested in doing this, without any replies so far. Perhaps you can help me get in touch with the people behind VODO, Public Domain Torrents, Public Domain Movies and Public Domain Review to try to convince them to add more metadata to their movie entries?
Another way you could help is by adding pages to Wikipedia about movies that are legal to distribute on the Internet. If such page exist and include a link to both IMDB and The Internet Archive, the script used to generate free-movies-archive-org-wikidata.json should pick up the mapping as soon as wikidata is updates.