For anyone looking for this kind of tool, I recommend checking out ViDL for downloading video content from websites on to your computer.
ViDL for Mac - Download Web Videos Easily:
ViDL is a free Mac app that allows you to easily download videos from YouTube and hundreds of other websites for offline viewing.
It is based on the popular youtube-dlcommand line tool, but much easier to use, especially with videos/playlists that require a login (like your personal "Watch Later" list).