Provides an authoritative voice and/or makes a course more understandable for the learner. Learners prefer the narration to be a friendly human voice rather than a machine voice.
Sound effects can be used to give the content a certain feel. Sounds can enhance the mood.
Times when audio is essential; Pronunciation of languages to hear how a native speaker pronounces the words and stresses the phrases.
Audio is great for accessibility. It provides options for users that have reading or learning difficulties.
Images tell a story. They can enhance pieces of text or show visually what the text or audio is saying.
Images can be used for decorative purposes to bring a page to life and create visual interest.
Images can break up text to give breathing space in the course or used as section markers within the content.
The choice is wide and varied, generic images can be used, as well as content-specific images like screenshots or diagrams.
Videos are great at showing users how to do something - for example, walkthroughs and software explainers. Learning by doing/viewing is one of the most effective learning methods. Videos can explain complex concepts more effectively than standalone text.
Video can be used decoratively allowing the page to come to life by adding movement.