In reply to Yerliteknoloji.

It’s true they are out of fashion and have accessibility issues and yes they will slow down your site especially if it’s above the fold and not lazy loaded.

Here’s a snippet from another blog:

As minimalist design and speedy sites are in overwhelming demand, video backgrounds are, thankfully, becoming a thing of the past in favor of fast-loading word-only hero areas and bold text.

Video backgrounds were a pain; not only did they demolish site speeds, they were often not compliant with WCAG 2.2.2 success criterion. They were distracting and would often change backgrounds making any text on top unreadable. We say good riddance to video backgrounds!