There are hundreds of apps on Google Play which claim to download youtube videos. However most of them are either fake or not functional. Youtube recently added a feature using which it is possible to download youtube videos. But it stores it only for two days.
We all know that youtube-dl provides us a 100% effective way to download videos from youtube. In this post I will show you how to do this:
Install python. See this Installing python on Android.
Download and transfer youtube-dl to your phone (you can do this directly on your phone if you don't have adb)
Then open terminal on your android device and do this: