Get a youtube thumbnail and save it into the media library

gistfile1.php

<?php

// This needs to get moved to the fuctions area
function nuvo_add_img_title( $attr, $attachment = null ) {
    $attr['title'] = trim( strip_tags( $attachment->post_title ) );
    return $attr;
}
add_filter( 'wp_get_attachment_image_attributes','nuvo_add_img_title', 10, 2 );

/*
 * Download an image from the specified URL and attach it to a post.
 * Modified version of core function media_sideload_image() in /wp-admin/includes/media.php  (which returns an html img tag instead of attachment ID)
 * Additional functionality: ability override actual filename, and to pass $post_data to override values in wp_insert_attachment (original only allowed $desc)
 *
 *
 * @param string $url (required) The URL of the image to download
 * @param int $post_id (required) The post ID the media is to be associated with
 * @param bool $thumb (optional) Whether to make this attachment the Featured Image for the post (post_thumbnail)
 * @param string $filename (optional) Replacement filename for the URL filename (do not include extension)
 * @param array $post_data (optional) Array of key => values for wp_posts table (ex: 'post_title' => 'foobar', 'post_status' => 'draft')
 * @return int|object The ID of the attachment or a WP_Error on failure
 */
function nuvo_attach_external_image( $url = null, $post_id = null, $thumb = null, $filename = null, $post_data = array() ) {
    if ( !$url || !$post_id ) return new WP_Error('missing', "Need a valid URL and post ID...");
    require_once( ABSPATH . 'wp-admin/includes/file.php' );
    // Download file to temp location, returns full server path to temp file, ex; /home/user/public_html/mysite/wp-content/26192277_640.tmp
    $tmp = download_url( $url );

    // If error storing temporarily, unlink
    if ( is_wp_error( $tmp ) ) {
        @unlink($file_array['tmp_name']);   // clean up
        $file_array['tmp_name'] = '';
        return $tmp; // output wp_error
    }

    preg_match('/[^\?]+\.(jpg|JPG|jpe|JPE|jpeg|JPEG|gif|GIF|png|PNG)/', $url, $matches);    // fix file filename for query strings
    $url_filename = basename($matches[0]);                                                  // extract filename from url for title
    $url_type = wp_check_filetype($url_filename);                                           // determine file type (ext and mime/type)

    // override filename if given, reconstruct server path
    if ( !empty( $filename ) ) {
        $filename = sanitize_file_name($filename);
        $tmppath = pathinfo( $tmp );                                                        // extract path parts
        $new = $tmppath['dirname'] . "/". $filename . "." . $tmppath['extension'];          // build new path
        rename($tmp, $new);                                                                 // renames temp file on server
        $tmp = $new;                                                                        // push new filename (in path) to be used in file array later
    }

    // assemble file data (should be built like $_FILES since wp_handle_sideload() will be using)
    $file_array['tmp_name'] = $tmp;                                                         // full server path to temp file

    if ( !empty( $filename ) ) {
        $file_array['name'] = $filename . "." . $url_type['ext'];                           // user given filename for title, add original URL extension
    } else {
        $file_array['name'] = $url_filename;                                                // just use original URL filename
    }

    // set additional wp_posts columns
    if ( empty( $post_data['post_title'] ) ) {
        $post_data['post_title'] = basename($url_filename, "." . $url_type['ext']);         // just use the original filename (no extension)
    }

    // make sure gets tied to parent
    if ( empty( $post_data['post_parent'] ) ) {
        $post_data['post_parent'] = $post_id;
    }

    // required libraries for media_handle_sideload
    require_once(ABSPATH . 'wp-admin/includes/file.php');
    require_once(ABSPATH . 'wp-admin/includes/media.php');
    require_once(ABSPATH . 'wp-admin/includes/image.php');

    // do the validation and storage stuff
    $att_id = media_handle_sideload( $file_array, $post_id, null, $post_data );             // $post_data can override the items saved to wp_posts table, like post_mime_type, guid, post_parent, post_title, post_content, post_status

    // If error storing permanently, unlink
    if ( is_wp_error($att_id) ) {
        @unlink($file_array['tmp_name']);   // clean up
        return $att_id; // output wp_error
    }

    // set as post thumbnail if desired
    if ($thumb) {
        set_post_thumbnail($post_id, $att_id);
    }

    return $att_id;
}

//Get the youtube thumbnail before we download it
$post_id = get_the_ID();
$youtubeimg = get_field('youtube_video_main');
$youtubeimgurl = 'http://img.youtube.com/vi/' . $youtubeimg . '/maxresdefault.jpg';

//Get the title of the image from the youtube video
$content = file_get_contents("http://youtube.com/get_video_info?video_id=" . $youtubeimg);
parse_str($content, $ytarr);
$newfilename = $ytarr['title'];

//This code loads the thumbnail from youtube and saves it in the Media Library
if ( has_post_thumbnail() ) {
	//Do nothing if the page has a featured image
}
else {
    //This calls the fuction
	nuvo_attach_external_image( $youtubeimgurl  ,  $post_id , 1 , $newfilename , array('post_title' => $newfilename ) );
}

// This needs to be removed and is just for testing
if ( has_post_thumbnail() ) {
	$large_image_url = wp_get_attachment_image_src( get_post_thumbnail_id(), 'large' );
	the_post_thumbnail( 'thumbnail' );
}