Transcripts are text alternatives to watching and listening to audio and video content. They should include both transcribed audio content and descriptions of sounds or noises that are important for context, as well as descriptions of any visual information.
Captions and subtitles are a text-version of audio content, synchronized to the audio and/or video and typically displayed in the media player used to access the content. They offer greater accessibility to people who cannot hear audio or who process written information better than audio, and can also be applied for spoken audio translated into another language.