The following example should do the trick, it will replace the content in src and href with the new url.
https://animalfarmxyz.com/iframe/?url=(monkey.aspx)
https://animalfarmxyz.com/iframe/?url=(abc.jpg)
https://animalfarmxyz.com/iframe/?url=(http://www.monkey.com/a2.aspx)
https://animalfarmxyz.com/iframe/?url=(../xxx.jpg)
<?php
$text = '<a href="/KB/answers/monkey.aspx" </a> abcd
<img src="abc.jpg" other="fssdf" /> ya di ya
di ya bold<a href="http://www.monkey.com/a.aspx" </a> abcd
<img src="../xxx.jpg" other="fssdf" /> ya di ya
di ya bold';
$check_hash = preg_match_all("/(?:href|src)=[\"|']?(.*?)[\"|'|>]+/", $text, $hashtweet);
foreach ($hashtweet[1] as $ht){
$newUrl = 'https://animalfarmxyz.com/iframe/?url=(' . $ht . ')';
echo $newUrl . '<br/>';
$text = str_replace($ht,$newUrl,$text);
}
echo $text;
?>