After uploading your video to YouTube, you are brought to a page where you can fill in the information about your video. There is a box on the right hand side that is titled "Privacy Settings." Under this drop down select "Unlisted" to allow only those whom you provide the URL to the ablily to watch your video.
If Uploading to Vimeo
As your video is uploading, the following tool bar appears. Under "Privacy Settings," select "Only people with a password" and set the password to "TEDx" (lowercase "x").
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