How do I download Youtube videos for offline viewing on an iOS device? I have just tried 28 different apps that claim to download youtube videos for offline viewing/listening, including Instapaper and Pocket.

None of them do it; they all expect there to be an internet connection.

Is there just .... 1 app .... that works?
YouTube currently offers this within their app if you pay the premium of $9.99 USD per month for what they call YouTube Red

Key Features according to their marketing is:


YouTube Music 
Ad free &amp; offline video
Orginal Shows