The plugin is called, Videopack (formerly Video Embed & Thumbnail Generator). It can be found at... https://wordpress.org/plugins/video-embed-thumbnail-generator/
As the name implies, the plugin uses FFMPEG to create a thumbnail in the form of a jpg file for any video file uploaded to the Wordpress media library.
The plugin requires classic editor, the Add Media button is necessary, in order to access the Wordpress media library.
Is there a way for wpForo with advanced attachments to use the classic editor?