The YouTube app Go will allow you to save the videos
Google released the YouTube app Go, which is intended for residents of the regions with slow access to the Internet.
At the moment the app is in the beta testing stage, it provides users the ability to save videos for future viewing without Network access.
Yet, users have two permissions (Basic Quality and Standard Quality 144p — 360p) to high definition videos are not available.
Downloaded videos can be share via Bluetooth, the app is not available in all regions.