从网站播放youtube链接

Question

我有以下PHP代码，我不知道为什么在Android手机和Mac上它下载Youtube视频文件而不是播放视频。

<?php

$feedURL = 'http://gdata.youtube.com/feeds/api/users/UCfLFTP1uTuIizynWsZq2nkQ/uploads?max-results=1';
$sxml = simplexml_load_file($feedURL);
$i = 0;
foreach ($sxml->entry as $entry) {
    $media = $entry->children('media', true);
    $watch = (string) $media->group->player->attributes()->url;
    $thumbnail = (string) $media->group->content[0]->attributes()->url;
    ?>
    <iframe width="330" border="0" height="220" style="width: 330px;" src="<?php echo $thumbnail; ?>" frameborder="0" allowfullscreen></iframe>      
    <?php
    $i++;

}
?>