Trying to create a video that pops up on every player's hud on trigger activation

[Brattl12345 0]

Hey everyone! I've looked around almost everywhere about this but I haven't had any luck with any of it. I want to have an overlay video or gif pop up on screen while the players are being transported to the frontline just like how RubixRaptor does in his video "Mankind Against Impossible Odds" at 0:58. Another example is in another RubixRaptor video, "A Really Bad Day at Installation 04 at 7:15. Is there a function or anything like that i can use as a trigger for players to activate when they walk through it?