CapScribe is an open-source application to help you add captions and/or audio description to audio and video files. Here's their explanations of what captions and video descriptions are:
Captions provide viewers with text-based, verbatim dialog, background sounds, and sound effects, key for deaf and hard of hearing viewers, and beneficial for hearing viewers as well.
Video descriptions provide verbal descriptions of what is happening visually in the video. Description makes it possible for people with vision disabilities to more fully comprehension the video. Sighted people may find video description benficial as well!
It's great to see an application like this available for free - captioning and video description programs can often run to hundreds of dollars, well out of the reach of casual or non-professional users.
- Ricky Buchanan