Load times: Yes, video files tend to be big, particularly if they’re in HD. The very first thing you have to do if you want attention is make sure your website loads quickly. A page that has to load a big video file is going to lose out, big time. Each second counts. But think again. How often are you going to need a video background in full HD? The goal is visual impact, not hyperrealism. High resolution video backgrounds will fight for attention with other content on the page. A 1280 or lower resolution file of a 10 second clip could achieve the effect you want and, with compression, be reduced to a load size of around 2Mb or less.
Hosting: In theory you can host the files for your video backgrounds with third party providers such as YouTube, Vimeo, Wistia or others. In practice, this is rarely ideal. No- and low-cost providers won’t give you full control over the appearance of your backgrounds. Even with a paid-for hosting service you’ll have to request the video stream from your third party supplier each time the page is visited, adding precious milliseconds to your load time. The alternative is to host your video backgrounds on your own server or via an appropriate Content Delivery Network (CDN). Given the likely size of the files, this is less of a problem than might appear and puts you in full control of the compression, performance and playout conditions.
Mobile: Provide a fall-back still image to display for backgrounds on mobile and for users with bandwidth limitations.
Audio: Video backgrounds load on autoplay, so make sure to mute the audio. The sudden shock of an unexpected soundtrack is pretty much a guaranteed backclick!