On my new project, members are able to use my YouTube API and it will generate a tag like below for them to use it in whatever textarea they want:

<ymedia>http://www.youtube-nocookie.com/v/qQG0XfU-bFs</ymedia>

I want my PHP profile page to take the string between <ymedia></ymedia> and generate a similar code below using $ymstring for the string collected from the ymedia tag:

<?php
$u_agent = $_SERVER[''HTTP_USER_AGENT''];
if(preg_match(''/Opera/i'',$u_agent)){
<object width="320" height="240" data="".$ymstring."?fs=1&hl=en_US&rel=0"><param name="movie" value="".$ymstring."?fs=1&hl=en_US&rel=0" /><param name="allowFullScreen" value="true" /><param name="wmode" value="transparent" /><param name="bgColor" value="#ffffff" /><param name="flashvars" value="vu=".$ymstring."?fs=1&hl=en_US&rel=0" /></object>
} else {
<object width="320" height="240"><param name="movie" value="".$ymstring."?fs=1&hl=en_US&rel=0"></param><param name="allowFullScreen" value="true"></param><param name="allowscriptaccess" value="always"></param><embed src="".$ymstring."?fs=1&hl=en_US&rel=0" type="application/x-shockwave-flash" allowscriptaccess="always" allowfullscreen="true" width="320" height="240"></embed></object>
}
?>

Basically, I'm trying to find all the ymedia tags in a $string and replace them with my youtube coding above aimed at either Opera or the rest of other browsers.

This should work:

preg_match("/<ymedia>(.*?)<\/ymedia>/", $Input, $Matches);

Then, your result would be in $Matches[1] which you could pass as $ymstring.