String to YouTube Embedding and Hyperlinks (HTML SAFE!!!)

Given a string $body, the functino string_to_links_and_embedded() will return a string where all youtube video links are converted to embedded objects and links such as 'google.com' are converted to click-able hyperlinks. The rest of the $body is htmlspecialchars() so it is safe for displaying on a website.

<?php
function link_array_sort($a, $b){
    if($a[1] == $b[1]){
        return 0;
    }
    return ($a[1] < $b[1]) ? -1 : 1;
}

function string_to_links_and_embedded($body){
    $pattern[0] = '#(http:\/\/)?(www\.)?youtube\.com/watch\?((&?v=([a-zA-Z0-9_-]+))|(&?[a-zA-Z0-9_-]+=[a-zA-Z0-9_-]+))*#';
    $pattern[1] = '#((?!.*com\/embed\/.*)(?!.*com\/watch?.*)(http:\/\/)?(www\.)?[a-zA-Z0-9_-]+\.[a-zA-Z]+(\/[a-zA-Z0-9]*)*(\/?\?[a-zA-Z0-9]+=[a-zA-Z0-9_-]+(&[a-zA-Z0-9]+=[a-zA-Z0-9_-]+)*)*)#';

    $replacement[0] = '<iframe width="560" height="315" src="http://www.youtube.com/embed/$5" frameborder="0" allowfullscreen></iframe>';
    $replacement[1] = '<a href="$1" target="_blank">$1</a>';

    preg_match_all($pattern[0], $body, $youtube, PREG_OFFSET_CAPTURE);
    preg_match_all($pattern[1], $body, $hyperlinks, PREG_OFFSET_CAPTURE);

    $links = array_merge($youtube[0], $hyperlinks[1]);

    usort($links, link_array_sort);

    print_r($links);

    $output = "";
    if(!empty($links)){
        $match_array_length = count($links);
        $start = 0;
        foreach($links as $key => $value){
            $match_start = $value[1];

            $output .= htmlspecialchars(substr($body, $start, $match_start - $start));

            if($value[0] == preg_replace($pattern[1], $replacement[1], $value[0])){
                $output .= preg_replace($pattern[0], $replacement[0], $value[0]);
            }else{
                if(preg_match("/https?/", $value[0]) == 0) {
                    $subject = 'http://'.$value[0];
                }else{
                    $subject = $value[0];
                }
                $output .= preg_replace($pattern[1], $replacement[1], $subject);
            }

            $start = $match_start + strlen($value[0]);

            if(($match_array_length - $key) == 1){
                $output .= substr($body, $start);
            }
        }
        return $output;
    }else{
        return htmlspecialchars($body);
    }
}