In some situations when Final Cut Pro X is installed (such as on mass, in a group install environment) the “Download additional content…” option in the FCPX menu doesn’t work as expected. I’ve seen people posting online asking how to otherwise get this content. Here’s the links you need.

Additional Content for Final Cut Pro X

Final Cut Pro X Content v1.0
Download from here

Pro Codecs for Final Cut Pro X and Quicktime

Pro Video Formats 2.0.1
Download from here