Source
File: wp-includes/class-wp-embed.php
public function __construct() {
// Hack to get the [embed] shortcode to run before wpautop().
add_filter( 'the_content', array( $this, 'run_shortcode' ), 8 );
add_filter( 'widget_text_content', array( $this, 'run_shortcode' ), 8 );
// Shortcode placeholder for strip_shortcodes().
add_shortcode( 'embed', '__return_false' );
// Attempts to embed all URLs in a post.
add_filter( 'the_content', array( $this, 'autoembed' ), 8 );
add_filter( 'widget_text_content', array( $this, 'autoembed' ), 8 );
// After a post is saved, cache oEmbed items via Ajax.
add_action( 'edit_form_advanced', array( $this, 'maybe_run_ajax_cache' ) );
add_action( 'edit_page_form', array( $this, 'maybe_run_ajax_cache' ) );
}