By default, WordPress does not allow you to auto embed a URL in a Text widget. You can autoembed into a post or a page by default.
The following php code was added to the functions.php file in the WordPress child theme.
// To be able to put an auto-embed URL into a Text widget just as // you can in a post or page, the following two lines of code are // entered here. Source: page 501 of WordPress The Missing Manual // Second Edition by Matthew MacDonald. add_filter('widget_text', array($wp_embed, 'run_shortcode'),8); add_filter('widget_text', array($wp_embed, 'autoembed'),8);