Sometimes I need to download game video walkthrough from Youtube to watch them later offline.
Also if you Youtuber this will be interest for you too.
I make two builds of chromium based browsers – they have functions to download video/audio from YouTube and other streaming services.
In Cenbrowser place mouse over video on Youtube and you will see download button (arrow to down) and you will be redirected to the service which allow you to select quality of media and download it.
SRWare Iron Youtuber version – have build in extension – it place button under video canvas and you can select what to download (video, only video, only sound from video).