[WordPress General] カスタムヘッダーを利用してスライドショー画像を入れ替えできるようにする

$custom_header_defaults = array(
    'default-image' => get_template_directory_uri().'/img/frontpage_slide.jpg',
    'width'         => 1200,
    'height'        => 800,
    'header-text'   => false, //画像にテキストをかぶせるか
);
add_theme_support( 'custom-header', $custom_header_defaults );

function frontpage_slides() {
    $header_images = get_uploaded_header_images();
    if ($header_images) {
        $str = NULL;
        foreach ($header_images as $key => $value) {
            $str .= '{image: "' . $value['url']  . '"},';
        }
        $data = rtrim($str, ',');
    } else {
        $data = '{image: "' . get_template_directory_uri() . '/img/frontpage_slide.jpg"}';
    }
    return $data;
}

<script type="text/javascript">
  $(document).ready(function(){
    'use strict';
    $.supersized({
      slide_interval: 10000,
      transition: 1,
      transition_speed: 3000,
      slides: [<?php echo frontpage_slides(); ?>]
    });
  });
</script>