Vocaleyes: Guidelines for Digital Accessibility
Guidelines for Digital Accessibility (including Audio Description on film):
http://vocaleyes.co.uk/services/museums-galleries-and-heritage/resources/guidelines-for-digital-accessibility-film/
See also Stagetext guidelines for adding captions to increase further access: https://www.musedcn.org.uk/2017/11/19/captioning-your-films-and-videos-stagetext/