Does the extra loading time that a background video has, affect SEO? Or that does not really affect it because the HTML already loaded and the video is just streaming after?
Does it make a difference (in terms of SEO) if the video is embedded using the
Yes a video background does effect your SEO see https://support.google.com/adsense/answer/6196932?hl=en and http://searchengineland.com/mobilegeddon-beginning-not-ending-220512
The slower your site loads the farther Google pushes you down the SERPs. The biggest concern for Google is mobile devices.
So what should you do instead of adding a video background? Research Sales Copywriting, customers care about your website solving their problem more than anything else. It's hard for a video that's a background to solve any problem unless that customer is looking for flash.
- Maybe, but the main goal of your site should be to create something users love. Your website could look terrible and very plain and outdated however if users find it valuable you'll get backlinks and organic traffic. See http://craigslist.org for a shining example.
Google measures the speed of your page using Googlebot. If the page load event doesn't happen for 10 seconds, Google may directly penalize your page.
Google pays attention to user experience. If users turn back to Google too look for something else, Google notices. If your video is loading so slowly that it makes your site appear to load slower to users, then users will turn back. In my experience, three seconds appears to be the magic number. If your page can load in under three seconds, users won't turn back to Google enough to affect your rankings.
So for background video, make sure that your page is useable and that the page load event can happen even before the video loads. If you do so, an unloaded video shouldn't change the user experience or SEO.
The technology you use for embedding the video doesn't matter unless some of them make it harder to allow the rest of the page to be useable when the video is loading.