How can I embed a YouTube video in OneNote?
If you want to embed video for playback in the note itself, I don't believe that is possible, or I haven't figured out a way to do it.
I know if you add Windows media type files, OneNote will use an internal player for playback, but it opens the video in its own window. (It would be nice if you could add notes to the video at specific times/frames.)
The best I've done for YouTube is downloading the video and then dropping the .flv file in as a link. OneNote will use an external player when you click for the video. There are browser extensions that allow you to grab the video from a specific YouTube page. This does have the advantage of keeping the video for as long as you keep the note files.