OOTB Sitecore doesn’t have support for any CDN integration. This module will help Media Manager to upload their media to Amazon S3 directly.
Most of the page load time is generally consumed by images and videos of that page. Instead of keeping all the resources on one server, you can put some resources such as heavy images and videos on another server.This other server will be treated as CDN server and this technique is called CDN.
So instead of storing all the media items in the Sitecore Media Library or the server database (which adds more load onto the server), we can store them in a CDN cloud. Sitecore provides a CDN connector which allows developers to route all media requests (dynamic and static) through a proxy CDN which allows for run-time, rule based rewriting of dynamic and static media URLs in your site renderings.It is designed to be plug-n-play requiring no additional development effort other than configuration.
Platform: Sitecore WCM