As a web dev I always have this in mind but the challenge is convincing your client who wants a video background. Maybe we need a media query that detects internet speed.
I find video backgrounds ridiculous most of the time (though they can be done really well), but that's not the real problem here - the real problem is including 200-800kb javascript code that does nothing but track your user, and often enough doesn't do it for you! (Hi Facebook!)
The real problem is using massive js frameworks for the sake of adding dynamic functionality to your site that, often enough, isn't actually worth it.
The real problem is that very often, these "features" are only as necessary as the marketing team says they are... the people who have the ability to ask "why?" and the ability to understand "why not" don't have the voice (or guts...) to do so.
The marketing team was surprised to learn how big the file was since the outsourced team "ensured" them that the new website would be lightweight. Oh well... Now the video has been reduced to a 16MB at 720p, which is still ludicrous to me, but they just really like having the video on the home page more than they want a truly lightweight page.
And to be fair, the video does not load when viewed on a mobile device, so at least there's that.