How does what work? The flash tag? Or the youtube tag?
the flash tag works like this:
[flash=width,height]content[/flash]
so if you have an embed query like this (flash from vimeo):
<div class="html" id="{CB}" style="font-family: monospace;"><ol><span style="color: #009900;">[url=http://december.com/html/4/element/iframe.html]<span style="color: #000000; font-weight: bold;"><iframe[/url] width="100%" height="166" scrolling="no" frameborder="no" src="http://w.soundcloud.com/player/?url=http%3A%2F%2Fapi.soundcloud.com%2Ftracks%2F19800055&show_artwork=true"<span style="color: #000000; font-weight: bold;">><span style="color: #009900;"><span style="color: #000000; font-weight: bold;"></iframe>
you can find the url that it's all about, in this case:
<div class="html" id="{CB}" style="font-family: monospace;"><ol>http://w.soundcloud.com/player/?url=http%3A%2F%2Fapi.soundcloud.com%2Ftracks%2F19800055<span style="color: #ddbb00;">&show_artwork=true
<span style="color: #ddbb00;">
<span style="color: #ddbb00;">
<span style="color: #ddbb00;"></span
so you put that in the 'content' area of the flash tags, and specify a width and height:
[flash=800,167]http://w.soundcloud.com/player/?url=http%3A%2F%2Fapi.soundcloud.com%2Ftracks%2F19800055&show_artwork=true[/flash]
and this is the result:
[flash=800,167]http://w.soundcloud.com/player/?url=http%3A%2F%2Fapi.soundcloud.com%2Ftracks%2F19800055&show_artwork=true[/flash]