abczoujin your MIME type configuration in the extension settings seems to be incorrect. Each value must be a valid regular expression. If you need help with the regular expression, please share a copy or screenshot of your MIME types / adapter settings in the admin panel.
jacobgrillo you should be able to get video to work by using the "just URL" template together with the AutoVideo feature in FoF Formatting https://discuss.flarum.org/d/17770-friendsofflarum-formatting
A more advanced player could definitely be implemented but I'm not sure if we want to include that in the extension itself. Doing a video player properly is quite complex, as it would require encoding the video in different formats as well as different qualities for best results. Other extensions can add custom templates to FoF Upload, so alternate video players could be plugged in that way.
