The original post only supports URL in the form "www.youtube.com". However, if you change to another form, like "youtube.com" or "tw.youtube.com", it will not work. So, we need to modify the original bb_config.xml as follows:
<!-- YouTube -->
<match name="youtube">
<regex>
(?i)\[youtube\]http\:\/\/(.*?)youtube.com\/watch\?v\=(.*?)\[/youtube\]
</regex>
<replace>
<![CDATA[
<object width="450" height="370">
<param name="movie" value="http://$1youtube.com/v/$2"></param>
<param name="wmode" value="transparent"></param>
<embed src="http://$1youtube.com/v/$2" type="application/x-shockwave-flash" wmode="transparent" width="450" height="370"></embed>
</object>
]]>
</replace>
</match>
Now, the new form of URL works.
See:
http://www.jforum.net/posts/list/4269.page