The Americans with Disabilities Act (ADA)  of 1990 requires that public programs and services be accessible to people with disabilities. For example, with captions, the content of a videotape shown in a course might be made accessible to a student who is deaf. If the product is not captioned, access to the content would need to be provided in another way, perhaps with a sign language interpreter. Similarly, if a student who is blind is enrolled in a course, the essential content that is presented visually could be spoken by the narrator, other speakers, or the instructor, or audio description could be provided as part of the product.
The Television Decoder Circuitry Act of 1990  requires that all television sets with screens 13 inches or larger manufactured for sale in the United States must have built-in closed-caption decoders. This Act has made it possible for millions of people to display closed-captioned televised materials in their homes, the workplace, and schools.
Section 713 of the Telecommunication Act of 1996  resulted in many changes in the broadcast and cable television industries. Among other things, it charged the Federal Communications Commission (FCC) to create mandates to increase the percentage of television programming that is captioned. It has published rules and set guidelines for increasing the number of captioned programs.
Section 508 of the Rehabilitation Act of 1973  requires that the federal government develop, procure, maintain, and use electronic and informational technology that is accessible to people with disabilities. In the 508 guidelines that were developed by the Access Board and became effective in 2001, all training and informational video productions that impart an agency's mission must contain captions for speech or other audio information necessary for the comprehension of the content, and critical visual content must be audio-described. Although the standards were developed for the federal government, additional legislation and voluntary compliance have extended their impact beyond federal agencies.
For more information, consult Creating Video and Multimedia Products That Are Accessible to People with Sensory Impairments. 
-  Americans with Disabilities Act (ADA)
-  Television Decoder Circuitry Act of 1990
-  Telecommunication Act of 1996
-  Section 508 of the Rehabilitation Act of 1973
-  Creating Video and Multimedia Products That Are Accessible to People with Sensory Impairments.