In this video we’ll learn how to create an interstitial, or pre-roll, video that plays before the WiFi login form is shown.

Also, be sure to add these domains to your network walled garden to ensure that the network allows the video to play:

i.ytimg.com
jnn-pa.googleapis.com
fonts.gstatic.com
play.google.com
*.googlevideo.com
static.doubleclick.net
googleads.g.doubleclick.net
yt3.ggpht.com
www.youtube.com
youtube.com

For example in UniFi, you must add the domains here: