Rights-Free and Rights-Light Media & Content: Licensing Video
Adding a Creative Commons License to YouTube Videos
To attach a Creative Commons license (YouTube only supports basic Attribution CC BY) to your YouTube video, go into the "Edit" view, and then select the Creative Commons option from the "License and rights ownership" menu. This will indicate to others that they may remix your video by making the "Remix this video!" button visible underneath of your video player. Read full insructions here.
Creative Commons licensed video by Flickr user Colleen Greene.