Collaboration can be used in multiple ways to help increase accessibility of educational resources. This fits with concepts of Universal Design for Learning that make educational information as accessible as possible for others.
In the article Making Videos Accessible with Universal Subtitles, George Williams explains how the website Universal Subtitles is encouraging people to collaborate to write subtitles through posting and editing transcripts of posted videos. You can upload a video to ask for subtitling and you can volunteer to subtitle.
I’m going to try something similar in my classes (although students will not be volunteers, but will probably get some sort of credit for it). I’m going to ask students to develop transcripts of narrated PowerPoints and videos that I develop or use for the class. I’ll let you know in a future post how (or whether) that works when I implement it in the Spring 2011 semester.
Ida's Blog 
I have used Universal Subtitles and have found it very user friendly. Good luck.