URL structure — a user

http://www.youtube.com/user/dansavage

To link to the page that lists all of an author's videos, do this:

URL structure — a video

Short URLs for a specific video:

To hyperlink to a specific place in a video:

You can cause a video to loop by adding &loop=1&autoplay=1 to the end of the URL

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To have a video play full-screen, use a link like this: http://www.youtube.com/v/AkyIfwFfAyM

URL structure — an embedded video

official documentation

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Search query syntax

For all search terms, see this page.