Text Transcript - REQUIRED.
For most media, such as recordings of speeches, you only need to make and post a transcript to provide basic accessibility.
Required only for relevant visuals not already covered in what's said. Audio description says what's in the visuals, so it's available to people who are blind. Most videos won't need audio description and you do not need an audio description is the video is only dialog between two people, however if those people are showing you something, then you will need to describe everything they are doing. For instance, if you are enrolling into student health insurance and the video shows the mouse clicking in the top right corner of the screen, then the audio description needs to tell you that the user is clicking in the top right corner of the screen. You will need audio description of things like charts and diagrams to describe what is actually happening in the chart, for users who cannot see the chart themselves.
Nice to have for most media, required for some. Captions are essentially transcripts synchronized with the video or audio. Media, such as audio-only recordings, will not require captions. Captions provide essential access for many students with hearing loss and can be a beneficial learning tool for others. There are many avenues to obtain or create captioned media and ensure that instructional materials are accessible. Even with videos that are only talking heads, it's good to have captions so that a person who is deaf or hard of hearing can see facial expressions. Some people will even appreciate captions for audio-only media, for example, if they are hard of hearing or non-native speakers and would like to listen yet also have the text to fill in what they can't hear or understand.
Including captions in a video is more complicated than a simple transcript. There are a variety of softwares or tools provided with online services such as: