As used by Khan Academy…

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Also see:

 

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 Addendum on 6/20/12:

  • Why and how to caption? — from Luis Perez
    The Collaborative for Communication Access via Captioning has created an excellent video showing how real people are impacted by the lack of captioning. The title of the video says it all: “Don’t Leave Me Out”.

 Addendums on 6/21/12:

Addendum on 7/2/12: