1) Log in to the Administrative Control Panel (ACP), and click the Posting tab.
2) Click Add new BBCode

3) In BBCode usage insert
Quote:
| [youtube]{TEXT}[/youtube] |
4) In HTML replacement insert
Quote:
| <embed src="http://www.youtube.com/v/{TEXT}" wmode="transparent" style="width:400px; height:326px;" id="VideoPlayback" type="application/x-shockwave-flash" flashvars=""> |
5) In the Help section put 'Use the ID of the Youtube video'.
6) Tick the box where it says 'Display on posting Page' then click on the Submit button

Now all you have to do to post the video in your forum is navigate to the posting screen, you will see a button called 'youtube'
Click the youtube button and put the ID of the video in between the tags for example:
Lets say your YouTube URL is - http://www.youtube.com/watch?v=xf69EEL3WBk
Then in between the youtube BBcode tags put 'xf69EEL3WBk' only.
As a result, the BBCode displayed would be
[youtube]xf69EEL3WBk[/youtube]

When you click Submit you will see your video displayed in the post like this:

7) Enjoy YouTube videos on your forum!
Guide written by SawanM, images added by Wild Cat