Advanced Search Widget is a WordPress post meta key and taxonomy searching plugin; compatible with all kind of post type and taxonomy from plugins and theme.
The default search engine of WordPress searches through all the post types title and content. This is not a big deal if you have a personal blog or a site with less than 200 post. But if you have an online store or a magazine sites with more than thousands of visits each day, then the database queries might be a big deal for you.
If your customers are on a category page that only lists the custom post types video, then they do not need to search through other post types like audio or images. So you can use this widget to let them only search for the post type video. This will reduce your database queries and serve the users need.