Wordpress: How to automatically attache youtube/vimeo thumbnail as a post feature image from a post meta key

functions.php

function insertThumbnail($data, $postArr) {
    if(!isset($postArr['ID'])) {
        return $data;
    }

    $postId = $postArr['ID'];
	$metaKey = 'you-post-meta-video-key'; // the custom meta key

    // If video and video format
    if(isset($postArr[$metaKey]) && ''!==$postArr[$metaKey] ) {
        
        $imageThumbnailUrl = ''; // the image remote url if any
        $videoUrl = $postArr[$metaKey]; // the post meta value givin' us the video url
        
        // Vimeo
        if(false!==strpos($videoUrl, 'vimeo')) {
            if(preg_match('/\/([\d]+)$/', $videoUrl, $reg)) {
                $vimeoId = $reg[1];
                // See http://stackoverflow.com/questions/1361149/get-img-thumbnails-from-vimeo
                $infoUrl = sprintf('http://vimeo.com/api/v2/video/%1$s.%2$s', $vimeoId, 'json');
                $ch = curl_init ($infoUrl);
		    	curl_setopt($ch, CURLOPT_HEADER, 0);
		    	curl_setopt($ch, CURLOPT_RETURNTRANSFER, 1);
		    	curl_setopt($ch, CURLOPT_BINARYTRANSFER, 1);
		    	$vimeoRawData=curl_exec($ch);
		    	curl_close ($ch);

                $vimeoData = @json_decode($vimeoRawData);
                if(false!==$vimeoData) {
          	        $imageThumbnailUrl = $vimeoData[0]->thumbnail_large;
                }
            }
        }
        // Youtube
        else if(false!==strpos($videoUrl, 'youtube')) {
            if(preg_match('/.*v=([^&]+).*$/', $videoUrl, $reg)) {
                $youtubeId = $reg[1];
                $imageThumbnailUrl = sprintf('http://img.youtube.com/vi/%1$s/hqdefault.jpg', $youtubeId);
            }
        }

        // If any thumbnail, import the file locally and attach it to the post
        if(''!==$imageThumbnailUrl) {
            $filename = 'tripmemore-' . $postArr['post_name'].'-' .md5($imageThumbnailUrl). '.jpg';
    
          	$uploadDirInfo = wp_upload_dir(); // @see http://codex.wordpress.org/Function_Reference/wp_upload_dir
            $targetFilePath = $uploadDirInfo['basedir'] . '/' . $filename;
            $targetFileUrl = $uploadDirInfo['baseurl'] . '/' . $filename;

    		// Copy image in local
    		$ch = curl_init ($imageThumbnailUrl);
		    curl_setopt($ch, CURLOPT_HEADER, 0);
		    curl_setopt($ch, CURLOPT_RETURNTRANSFER, 1);
		    curl_setopt($ch, CURLOPT_BINARYTRANSFER, 1);
		    $raw=curl_exec($ch);
		    curl_close ($ch);

		    $fp = fopen($targetFilePath,'x');
		    fwrite($fp, $raw);
		    fclose($fp);

		    // Create the attachment
		    $wp_filetype = wp_check_filetype($targetFilePath, null );
		    $attachment = array(
	            'guid' => $filename,
	            'post_mime_type' => $wp_filetype['type'],
	            'post_title' => sanitize_file_name($filename),
	            'post_content' => '',
	            'post_status' => 'inherit'
		    );
		    $attach_id = wp_insert_attachment( $attachment, $filename);
		    
            // Set the thumbnail as feature image
            require_once(ABSPATH . 'wp-admin/includes/image.php');
            $attach_data = wp_generate_attachment_metadata( $attach_id, $targetFilePath );
            $res = wp_update_attachment_metadata( $attach_id, $attach_data );
  
            $res = set_post_thumbnail( $postId, $attach_id );

            // Update the post meta
            update_post_meta($postId, $metaKey, $postArr[$metaKey]);
        }
    }
    return $data;
}

add_filter( 'wp_insert_post_data', 'insertThumbnail', '95', 2 ); // @see http://codex.wordpress.org/Plugin_API/Filter_Reference/wp_insert_post_data