<?php
    $cont = '<div class="video-image">
        <a href="video/TI - No+Matter+What/_CHheEQe9M8/" title="23">
            <img src="http://i.ytimg.com/vi/_CHheEQe9M8/3.jpg" alt="TI" width="130" height="78"/>
        </a>
        <span class="video-title"><a href="video/TI - No+Matter+What/_CHheEQe9M8/" title="sdg">No Matter What</a></span>
        <span class="video-artist"><a href="video/TI - No+Matter+What/_CHheEQe9M8/" title="ss" class="ellipsis">TI</a></span>
    </div>';

    if (preg_match_all('#<a href="([^>]*)"#iU', $cont, $arr))
    {
        foreach ($arr[1] as $value)
        {
            var_dump($value);
            $cont = preg_replace('#' . preg_quote($value, '#') . '#iU', 'http://site.com/' . $value, $cont);
        }
    }

    echo $cont;

Döndürdü: http://site.com/http://site.com/http://site.com/video/TI - No+Matter+What/_CHheEQe9M8/

Why? I want : http://site.com/video/TI - No+Matter+What/_CHheEQe9M8/ How to do it? sorry for bad english

EDIT

$dom = new DOMDocument;
    $dom->loadHTML($cont);
    foreach( $dom->getElementsByTagName('a') as $node )
    {
        $cont = preg_replace('#' . preg_quote($node->getAttribute('href'), '#') . '#', "http://site.com/" . $node->getAttribute('href'), $cont);
    }    
    echo $cont;

De bu kod döndürür http://site.com/http://site.com/http://site.com/video/TI - No+Matter+What/_CHheEQe9M8/ ...