dosent work with uploaded video in website

No, it doesn’t – you’re right.

The plugin does not create thumbnails itself so much as automatically download the thumbnails created by YouTube, Vimeo, etc.

To create a thumbnail from a video you have uploaded to your site you will need some server side software installed like FFMPEG, which most hosts do not offer.

Why not just upload your video to YouTube (for public) or Vimeo (for private) anyway? They will likely give a better viewing experience as their servers are specifically setup for the job.