I am making some software that will need to play back mp4 videos (a small part of the application). The software has a mechanism built in so that I can unlock features after payment . The mechanism works in house and contacts no servers, the user simply puts in a key that is generated server side on a website after they put in their unique code.
My question is how can I hide my protection method (so people can’t make their own key gens) whilst still being “open source” and complying with the free FFMPEG licence?