I was ask why use closed captions on videos if you already have a description on the video. Well, we did a Hot Blog Tips Google Plus Hangouts on Air to answer the question.
As you will hear, you must do a description, but there is also a huge benefit to using Closed Caption when you can. As Brian D. Hawkins points out, there is more to closed captions than just putting text on a doc and uploading it.
Watch on youtube.com
We also have a blog post that you can checkout with links to How To Do Closed Captions For YouTube - see Can Search Engines Read Closed Captions And Descriptions On YouTube
Closed Captions on video is just being discovered by some people, get in ahead of your competition.