It can take some time to produce quality web video that can be used across browsers, devices, and disability categories. Ultimately, though, making the decisions necessary to select a standard format, such as MPEG-4 or H.264, or to go with a server that outputs in many formats, will leave you in a solid position as web video continues its rapid evolution.
Likewise, captioning has benefits that affect a large cross-section of the Web. According to the National Institutes of Health, 12% of all Americans—a staggering 36.4 million—have some kind of hearing trouble. And that’s before we add in situational disabilities, such as noisy environments, office PCs that come without speakers, or people who simply don’t like being distracted by audio. Caption files and transcripts are also plain text, which makes them searchable, and while search engines still struggle to find a strategy to index audio and video content, this also works to your advantage.
For an example of a video search engine, check out the DO-IT Video Search at http://www.washington.edu/doit/Video/Search/.
Audio descriptions aren’t as universally beneficial, but for the group of people who need them, they are indispensable. Still, it’s best to keep in mind the need for spoken confirmation of what’s going on as you produce video content, so that the amount you need to describe in order to be reasonably accessible is minimal.