Set the WordPress Post Thumbnail automatically from my ACF Vimeo Field: https://halgatewood.com/downloads/acf-vimeo-field

acf_vimeo_thumbnail_save_post.php

if( !function_exists('Generate_Featured_Image') )
{
  // FUNCTION FOUND ON GITHUB
	function Generate_Featured_Image( $image_url, $post_id  )
	{
	    $upload_dir = wp_upload_dir();
	    $image_data = file_get_contents($image_url);
	    $filename = basename($image_url);
	    if(wp_mkdir_p($upload_dir['path']))     $file = $upload_dir['path'] . '/' . $filename;
	    else                                    $file = $upload_dir['basedir'] . '/' . $filename;
	    file_put_contents($file, $image_data);
	
	    $wp_filetype = wp_check_filetype($filename, null );
	    $attachment = array(
	        'post_mime_type' => $wp_filetype['type'],
	        'post_title' => sanitize_file_name($filename),
	        'post_content' => '',
	        'post_status' => 'inherit'
	    );
	    $attach_id = wp_insert_attachment( $attachment, $file, $post_id );
	    require_once(ABSPATH . 'wp-admin/includes/image.php');
	    $attach_data = wp_generate_attachment_metadata( $attach_id, $file );
	    $res1 = wp_update_attachment_metadata( $attach_id, $attach_data );
	    $res2 = set_post_thumbnail( $post_id, $attach_id );
	}
}


function acf_vimeo_thumbnail_save_post( $post_id ) 
{ 
    // bail early if no ACF data
    if( empty($_POST['acf']) ) return;
    
    // array of field values
    $fields = (array) $_POST['acf'];

	if( $fields )
	{
		foreach( $fields as $field_key => $val )
		{
			$field = get_field_object($field_key, $post_id);
			if( $field['type'] != "vimeo" ) continue;
			
			$vimeo_id 		= acf_vimeo_parse_vimeo_id( $val );
			if( !$vimeo_id ) continue;
			
			$video_object 	= acf_vimeo_ping_api( $vimeo_id );
			
			if( $video_object and isset($video_object->thumbnail_large) )
			{
				$thumb640 	= $video_object->thumbnail_large;
				$thumb1280 	= str_replace("_640","_1280", $thumb640);
				Generate_Featured_Image( $thumb1280, $post_id );
			}
		}
	}
}

add_action('acf/save_post', 'acf_vimeo_thumbnail_save_post', 1);