You may think about an online course on the edX platform may as a framework containing several resources. Some of them like text content in HTML format and reference reading material in PDF format are stored on the edX server.
Other resources like still images and videos may better be stored elsewhere. That reduces the load on the course server and simplifies maintenance.
- Still images may be published for free on the web through Flickr or Imgur
- Videos may be published for free on the web through YouTube or Vimeo.
Presentation files may be published for free through SlideShare or Google Docs. Academic institutions may also offer suitable publication facilities. Better still is to use a full-fledged online repository and distribution system where you can store, curate/modify and fetch still images, videos and other files.
- Cloudinary is an easy-to-use solution that is free of charge for personal (and fully functional but limited) use. The free version is well suited for the PISA Global course.