In YouTube developers polices in G.2.a said "Selling an API Client"(https://developers.google.com/youtube/terms/developer-policies#g.-distribution-and-commercial-use), that mean a developer can make an app that using YouTube videos and sell the app / sell a monthly subscription to app users. my question is, if that doesn't violate copyright? It doesn't seem logical to me that YouTube wrote something illegal, that's clear, the question is how does it gets along with the fact that the owners of the videos have copyright
I googled it and tried to contact YouTube, but nothing.