Youtube API下载标题(使用PHP示例)

如果我在没有CC贡献的情况下尝试来自视频的曲目ID,我会得到正确的错误：

A service error occurred: The permissions associated with the request
are not sufficient to download the caption track. The request might
not be properly authorized,or the video order might not have enabled
third-party contributions for this caption.

我已经尝试在$youtube-> captions->下载中排除第二个可选参数,但没有运气.
当它试图打印$captionResource时它会中断(我是调试PHP的新手)

//(original from Youtube API examples)  
function downloadCaption(Google_Service_YouTube $youtube,$captionId,&$htmlBody) {
    // Call the YouTube Data API's captions.download method to download an existing caption.
    $captionResouce = $youtube->captions->download($captionId,array(
        'tfmt' => "srt",'alt' => "media"
    ));

    $htmlBody .= "<h2>Downloaded caption track</h2><ul>";
    $htmlBody .= sprintf('<li>%s</li>',$captionResouce);
    $htmlBody .= '</ul>';
}