Ask HN: Legal to stream copyrighted material from Dropbox?

A user has A video file that they want to watch on any platform with a browser. They put the file into a folder in their Dropbox and the video is encoded and stored in a place it can be streamed. Optionally, the video is uploaded to YouTube and Vimeo also. Does anyone do this? Would it be legal with copyrighted videos (without the YouTube option, of course)?