People who are blind cannot access the visual content of a video production unless the content is available in audio format as well. Being aware of this access issue during the design phase of a product can result in speakers or narrators voicing enough of the content to allow a person who is blind to follow along. This is particularly important for educational programming and products used with large audiences where it is generally unknown what visual impairments audience members may have. Producers can listen to their video product without viewing the screen to help determine how accessible it might be to a person who is blind.
Once a video product is complete, specially trained professionals can add audio content to the production. When pauses occur in the original production, the voice reads titles and speaker names and describes scenery, objects, and other visual information. Credits and contact information at the end of the production can also be voiced. Most video producers use outside services for audio description. Because this additional audio content is not of value to other audiences and can be distracting, audio description is usually not included with the standard product but is provided as an optional format. Providing this option is particularly important for educational products.
For more information, consult Creating Video and Multimedia Products That Are Accessible to People with Sensory Impairments. 
-  Creating Video and Multimedia Products That Are Accessible to People with Sensory Impairments.