One of the problems when using PowerPoint with video backgrounds is that if you move forward the slide then the video background will start over again and again. The smart guys behind PresenterMedia proposed here a simple solution to avoid this issue in PowerPoint and let you make professional PowerPoint presentations with a continuous looped video background. The solution is simple, instead of using slides use text shapes and animations with a single slide.
By watching the video on Youtube embedded on this article, you can learn how to use video backgrounds in your presentation and take advantage of the awesome video backgrounds that you can download from PresenterMedia.com
A list of useful presentation resources being offered online (free and paid) including presentation templates, video backgrounds, photos, clipart and animations.
Plenty of mind-numbing background music, but still worth checking further to see whether these "animated teaching videos for ESL and EFL learners" (About Us, ¶1, 2017.02.24 [JST]) might be suited to particular learners' needs