$re = '/(video.*?)%7bmatch%7d/';
$str = ' video://lots0fr@ndomcharact#Rsinbetweenof1nd1scrimin@length/%7bmatch%7d/lots0fr@ndomcharact#Rsinbetweenof1nd1scrimin@length
audio://lots0fr@ndomcharact#Rsinbetweenof1nd1scrimin@length/%7bmatch%7d/lots0fr@ndomcharact#Rsinbetweenof1nd1scrimin@length';
$subst = "$1REPLACEMENT_HERE";
$result = preg_replace($re, $subst, $str);
echo "The result of the substitution is ".$result;
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for PHP, please visit: http://php.net/manual/en/ref.pcre.php