This will only work on iPods,iPhones,and iPads :) And you can Download the videos using your device :)
Download the app "PlayTube"
To make sure it works,search for something random.
Click on the + beside of the video you want to download. Then on the bottom it says "Cache" and a red 1. That means it is downloading.
When you click "Cache" there would be all the videos that you have downloaded.
Now even if you don't have Wifi you can still watch these videos! Thanks for watching! Follow me and I will follow back!
The creator of this guide has not included tools