Move supporting files such as multimedia, fonts, JavaScript, and CSS, local to the publication or inside the application used for publishing. This helps ensure the vital components of the work can be easily packaged together, reduces ongoing maintenance, and helps ensure exports contain all necessary resources.
If this is impractical in the live environment, other guidelines may be relevant:
15. Develop a strategy to capture any external media content
16. Captions for non-text features add meaningful context
20. Ensure all core intellectual components of a work are reflected in the export package
29. Consider a preservation-specific EPUB in your workflow
51. Host media files local to the website