Is 8MB the largest upload size you offer with the WordPress portfolio grid gallery? I tried to add a video file but the video was way too large.
8MB is a limit from your web server.
You need to change the web server PHP configuration file to change the limit. If you are using a shared web hosting, you need to contact your web hosting provider and ask them to make the change.
Or you can upload the video file to your web server via FTP client software, then add the video URL link directly to the plugin.