Can't figure out with character encoding in PHP

I have put together little utility for reading youtube video tags. http://ift.tt/1Kg80CS

<?php
header("Content-Type: application/json");
error_reporting(E_ERROR | E_PARSE);
$_POST['fn']='http://ift.tt/1Kg80CU';
if(isset($_POST['fn']) && $_POST['fn'] != ''){
    $url = htmlentities($_POST['fn']);
    $page_content = file_get_contents('http://ift.tt/1Kg80CU');


    $dom_obj = new DOMDocument();
    if($dom_obj->loadHTML($page_content)){

        $dom_obj->loadHTML($page_content);
        $meta_val = '';

        foreach($dom_obj->getElementsByTagName('meta') as $meta) {

            if($meta->getAttribute('property')=='og:video:tag'){ 

                $meta_val = $meta_val.','.$meta->getAttribute('content');
            }
        }
        echo substr($meta_val,1);
    }
    else{
        echo "Invalid Url!";
    }
}
else{
    echo "Empty Url!";
}
?>

It works for ASCI characters but UTF characters show unreadable. I can't find the problem.