It only takes a few easy steps to download videos from the YouTube app. Open a video, tap the download button (see screenshot), select the resolution of the downloaded video and it will start to be obtained on your device. There is a new “Offline” section in the YouTube app, the place where you’ll find a list of all the movies that may currently be in the download queue or accessible to watch offline.
That said, there are obvious specific limitations. One, not all videos available on the YouTube website are available for purchase. Offline mode is generally disabled for music videos and in-app movies.
In addition, downloaded videos can only be watched on the YouTube app. I researched it on Android and it looks like YouTube saves movies in smaller pieces as .exo information, a format that is not supported on different media players.
However, there are no restrictions on the variety of movies you can take offline with the YouTube app; you may be limited only by the free storage available on your iPhone or Android phone.