Including accessibility features when a product is being developed is much easier than providing accommodations to viewers with sensory impairments once they need to access the media. Building in accessibility features for all instructional products is in keeping with principles of universal design.
Universal design is defined by the Center for Universal Design at North Carolina State University as "the design of products and environments to be usable by all people to the greatest extent possible, without the need for adaptation or specialized design" (http://www.design.ncsu.edu/cud/).
DVDs, streaming video on the web, and films are engaging instructional tools. Everyone benefits from dynamic visual displays and dialog. Well, not everyone. Viewers who are deaf miss all audio content that is not also presented in a visual form.
Those who are blind can access only the visual content that is also presented in spoken form. It is usually not difficult to make video and multimedia products accessible to viewers with sensory impairments, but special considerations should be made at the design phase to ensure complete access to everyone.