MongoDB是专为可扩展性，高性能和高可用性而设计的数据库。它可以从单服务器部署扩展到大型、复杂的多数据中心架构 ...

This tutorial explains how to download private videos & playlists, or rather: videos you need to be logged in for. I can't guarantee this will work for every service out there, but it for sure works ...