Source: https://www.drmare.com/itunes-tips/play-itunes-m4v-movies-offline.html
Product: https://www.drmare.com/m4v-converter-for-win
Home: https://www.drmare.com/
iTunes purchases and rental movies are combined with the FairPlay. Even if you download the iTunes movies offline, you need Internet connection such as Wifi to authorize your rentals or purchases to play offline. This is not so convenient when you are on airplane.
But don’t worry, if you’d rather play iTunes movies offline without with wifi, you can follow this quick video tutorial to convert iTunes movies with the DRmare M4V Converter.
source