lowed_media_types An array of allowed media types. Default media types are
	 *                                   'audio', 'video', 'object', 'embed', and 'iframe'.
	 */
	$allowed_media_types = apply_filters( 'media_embedded_in_content_allowed_types', array( 'audio', 'video', 'object', 'embed', 'iframe' ) );

	if ( ! empty( $types ) ) {
		if ( ! is_array( $types ) ) {
			$types = array( $types );
		}

		$allowed_media_types = array_intersect( $allowed_media_types, $types );
	}

	$tags = implode( '|', $allowed_media_types );

	if ( preg_match_all( '#<(?P<tag>' . $tags . ')[^<]*?(?:>[\s\S]*?<\/(?P=tag)>|\s*\/>)#', $content, $matches ) ) {
		foreach ( $matches[0] as $match ) {
			$html[] = $match;
		}
	}

	return $html;
}

/**
 * Retrieves galleries from the passed post's content.
 *
 * @since 3.6.0
 *
 * @param int|WP_Post $post Post ID or object.
 * @param bool        $html Optional. Whether to return HTML or data in the array. Default true.
 * @return array A list of arrays, each containing gallery data and srcs parsed
 *               from the expanded shortcode.
 */
function get_post_galleries( $post, $html = true ) {
	if ( ! $post = get_post( $post ) )
		return array();

	if ( ! has_shortcode( $post->post_content, 'gallery' ) )
		return array();

	$galleries = array();
	if ( preg_match_all( '/' . get_shortcode_regex() . '/s', $post->post_content, $matches, PREG_SET_ORDER ) ) {
		foreach ( $matches as $shortcode ) {
			if ( 'gallery' === $shortcode[2] ) {
				$srcs = array();

				$shortcode_attrs = shortcode_parse_atts( $shortcode[3] );
				if ( ! is_array( $shortcode_attrs ) ) {
					$shortcode_attrs = array();
				}

				// Specify the post id of the gallery we're viewing if the shortcode doesn't reference another post already.
				if ( ! isset( $shortcode_attrs['id'] ) ) {
					$shortcode[3] .= ' id="' . intval( $post->ID ) . '"';
				}

				$gallery = do_shortcode_tag( $shortcode );
				if ( $html ) {
					$galleries[] = $gallery;
				} else {
					preg_match_all( '#src=([\'"])(.+?)\1#is', $gallery, $src, PREG_SET_ORDER );
					if ( ! empty( $src ) ) {
						foreach ( $src as $s ) {
							$srcs[] = $s[2];
						}
					}

					$galleries[] = array_merge(
						$shortcode_attrs,
						array(
							'src' => array_values( array_unique( $srcs ) )
						)
					);
				}
			}
		}
	}

	/**
	 * Filters the list of all found galleries in the given post.
	 *
	 * @since 3.6.0
	 *
	 * @param array   $galleries Associative array of all found post galleries.
	 * @param WP_Post $post      Post object.
	 */
	return apply_filters( 'get_post_galleries', $galleries, $post );
}

/**
 * Check a specified post's content for gallery and, if present, return the first
 *
 * @since 3.6.0
 *
 * @param int|WP_Post $post Optional. Post ID or WP_Post object. Default is global $post.
 * @param bool        $html Optional. Whether to return HTML or data. Default is true.
 * @return string|array Gallery data and srcs parsed from the expanded shortcode.
 */
function get_post_gallery( $post = 0, $html = true ) {
	$galleries = get_post_galleries( $post, $html );
	$gallery = reset( $galleries );

	/**
	 * Filters the first-found post gallery.
	 *
	 * @since 3.6.0
	 *
	 * @param array       $gallery   The first-found post gallery.
	 * @param int|WP_Post $post      Post ID or object.
	 * @param array       $galleries Associative array of all found post galleries.
	 */
	return apply_filters( 'get_post_gallery', $gallery, $post, $galleries );
}

/**
 * Retrieve the image srcs from galleries from a post's content, if present
 *
 * @since 3.6.0
 *
 * @see get_post_galleries()
 *
 * @param int|WP_Post $post Optional. Post ID or WP_Post object. Default is global `$post`.
 * @return array A list of lists, each containing image srcs parsed.
 *               from an expanded shortcode
 */
function get_post_galleries_images( $post = 0 ) {
	$galleries = get_post_galleries( $post, false );
	return wp_list_pluck( $galleries, 'src' );
}

/**
 * Checks a post's content for galleries and return the image srcs for the first found gallery
 *
 * @since 3.6.0
 *
 * @see get_post_gallery()
 *
 * @param int|WP_Post $post Optional. Post ID or WP_Post object. Default is global `$post`.
 * @return array A list of a gallery's image srcs in order.
 */
function get_post_gallery_images( $post = 0 ) {
	$gallery = get_post_gallery( $post, false );
	return empty( $gallery['src'] ) ? array() : $gallery['src'];
}

/**
 * Maybe attempts to generate attachment metadata, if missing.
 *
 * @since 3.9.0
 *
 * @param WP_Post $attachment Attachment object.
 */
function wp_maybe_generate_attachment_metadata( $attachment ) {
	if ( empty( $attachment ) || ( empty( $attachment->ID ) || ! $attachment_id = (int) $attachment->ID ) ) {
		return;
	}

	$file = get_attached_file( $attachment_id );
	$meta = wp_get_attachment_metadata( $attachment_id );
	if ( empty( $meta ) && file_exists( $file ) ) {
		$_meta = get_post_meta( $attachment_id );
		$regeneration_lock = 'wp_generating_att_' . $attachment_id;
		if ( ! array_key_exists( '_wp_attachment_metadata', $_meta ) && ! get_transient( $regeneration_lock ) ) {
			set_transient( $regeneration_lock, $file );
			wp_update_attachment_metadata( $attachment_id, wp_generate_attachment_metadata( $attachment_id, $file ) );
			delete_transient( $regeneration_lock );
		}
	}
}

/**
 * Tries to convert an attachment URL into a post ID.
 *
 * @since 4.0.0
 *
 * @global wpdb $wpdb WordPress database abstraction object.
 *
 * @param string $url The URL to resolve.
 * @return int The found post ID, or 0 on failure.
 */
function attachment_url_to_postid( $url ) {
	global $wpdb;

	$dir = wp_get_upload_dir();
	$path = $url;

	$site_url = parse_url( $dir['url'] );
	$image_path = parse_url( $path );

	//force the protocols to match if needed
	if ( isset( $image_path['scheme'] ) && ( $image_path['scheme'] !== $site_url['scheme'] ) ) {
		$path = str_replace( $image_path['scheme'], $site_url['scheme'], $path );
	}

	if ( 0 === strpos( $path, $dir['baseurl'] . '/' ) ) {
		$path = substr( $path, strlen( $dir['baseurl'] . '/' ) );
	}

	$sql = $wpdb->prepare(
		"SELECT post_id FROM $wpdb->postmeta WHERE meta_key = '_wp_attached_file' AND meta_value = %s",
		$path
	);
	$post_id = $wpdb->get_var( $sql );

	/**
	 * Filters an attachment id found by URL.
	 *
	 * @since 4.2.0
	 *
	 * @param int|null $post_id The post_id (if any) found by the function.
	 * @param string   $url     The URL being looked up.
	 */
	return (int) apply_filters( 'attachment_url_to_postid', $post_id, $url );
}

/**
 * Returns the URLs for CSS files used in an iframe-sandbox'd TinyMCE media view.
 *
 * @since 4.0.0
 *
 * @return array The relevant CSS file URLs.
 */
function wpview_media_sandbox_styles() {
 	$version = 'ver=' . get_bloginfo( 'version' );
 	$mediaelement = includes_url( "js/mediaelement/mediaelementplayer.min.css?$version" );
 	$wpmediaelement = includes_url( "js/mediaelement/wp-mediaelement.css?$version" );

	return array( $mediaelement, $wpmediaelement );
}