What does your Video SEO plugin actually do?
It goes through a series of steps, as soon as you update a post that you put a Video in:
It recognises the Video and, depending on whether it's a self-hosted Video or hosted on a site like Vimeo, determines what to do;
If it's for instance hosted on Vimeo, it'll retrieve the Video details from the Vimeo API;
It'll determine which thumbnail to attach to the Video and what the duration of the Video is;
It then saves all this metadata so that you get a Video snippet in the snippet preview AND a Video XML Video entry is generated for the post / page.
It does all that on the fly, as soon as the plugin is activated you only have to add a Video to a post and it'll automatically recognize it and go through those steps for you.