If your video is not embedding, see if your link starts with "http:" - if it does, change it to "https:" and it will work.

If a video isn't embedded you should assume it may be inappropriate for some people.

How do I embed a Youtube video?
Simply post the YouTube URL.
Alternately (actually, this may no longer work):
Click the "youtube" button on the second row on the furthermost left side.
You will now have the words: [youtube][/youtube] in your editor.
Now, copy and paste the youtube video id (youtube.com/watch?v=oHg5SJYRHA0&x=y) in between the middle brackets in order for it to look like this:
    [youtube]oHg5SJYRHA0[/youtube]
and leave out this part of the link: "http://www.youtube.com/watch?v="

Or you can paste the YouTube link, highlight it, and then click on the "YouTube" button. This will encase the link in the youtube tags,
Now just click "post" and you're done!


How can I search if a video has been posted here before?
This is not foolproof, but it's a good start.
Search for the youtube ID (youtube.com/watch?v=oHg5SJYRHA0)