class-wp-embed.php

<?php
/**
 * API for easily embedding rich media such as videos and images into content.
 *
 * @package WordPress
 * @subpackage Embed
 * @since 2.9.0
 */
class WP_Embed {
	public $handlers = array();
	public $post_ID;
	public $usecache      = true;
	public $linkifunknown = true;
	public $last_attr     = array();
	public $last_url      = '';

	/**
	 * When a URL cannot be embedded, return false instead of returning a link
	 * or the URL.
	 *
	 * Bypasses the {@see 'embed_maybe_make_link'} filter.
	 *
	 * @var bool
	 */
	public $return_false_on_fail = false;

	/**
	 * Constructor
	 */
	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' ) );
	}

	/**
	 * Process the [embed] shortcode.
	 *
	 * Since the [embed] shortcode needs to be run earlier than other shortcodes,
	 * this function removes all existing shortcodes, registers the [embed] shortcode,
	 * calls do_shortcode(), and then re-registers the old shortcodes.
	 *
	 * @global array $shortcode_tags
	 *
	 * @param string $content Content to parse
	 * @return string Content with shortcode parsed
	 */
	public function run_shortcode( $content ) {
		global $shortcode_tags;

		// Back up current registered shortcodes and clear them all out
		$orig_shortcode_tags = $shortcode_tags;
		remove_all_shortcodes();

		add_shortcode( 'embed', array( $this, 'shortcode' ) );

		// Do the shortcode (only the [embed] one is registered)
		$content = do_shortcode( $content, true );