Background videos on mobile
Splash background videos are visually appealing, but can be complicated to deal with on mobile devices
By default if you're using a YouTube video background, when your clients view on a mobile device it will fall back to the YouTube thumbnail image. As long as you control the video, you'll want to make sure a thumbnail is set up.
If you have admin rights to the video, you will be able to set or change the thumbnail image via video settings on Youtube's side.