Download tubemate, then from youtube press share, select tubemate and you can download either audio or video, been using it for years and it's very reliable. The app is not found in the playstore so u have to search for it on google by typing tubemate apk file download, once done run the file so it installs.
before 2 years I was using tubemate but when I discovere I can download from internet explorer it's was very good even I download a video before 3 days but when I updated my phone I can't use the option of download
