My video background isn't playing on mobile

In Elementor, video backgrounds do not play on mobile. This is how the creators of Elementor intend for it to work which we imagine is because:

a) mobile phones don't have the same processing power as computers
b) they generally don't have as fast of internet 
c) they often are on cellular data which gets eaten up by large videos

However if you also add a background fallback image, then that will show on mobile instead of the video. That's our general recommendation and is how we have it setup on our demos. Example:

If you do want it to play on all devices instead of an image for mobile, you can try using Master Slider instead. There is a setting there that you can enable to make video backgrounds in the sliders play on all devices (though you'll see a note where the creators of Master Slider say they also don't recommend it). Personally we find Elementor is much easier to use and more intuitive than Master Slider, but it's certainly an option if you want it that way.

*Note - this information only applies to video backgrounds; standard video embeds will already play on all devices.