get post playlist like get_post_gallery()

We can look at get_post_galleries() for ideas how to handle playlists instead of galleries.

Here’s an untested modification based on the core function:

function wpse_get_post_playlists( $post, $html = true ) {
    if ( ! $post = get_post( $post ) )
        return array();

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

    $playlists = array();
    if ( preg_match_all( "https://wordpress.stackexchange.com/" . get_shortcode_regex() . '/s', $post->post_content, $matches, PREG_SET_ORDER ) ) {
        foreach ( $matches as $shortcode ) {
            if ( 'playlist' === $shortcode[2] ) {
                $ids = array();

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

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

                $playlist = do_shortcode_tag( $shortcode );
                if ( $html ) {
                    $playlists[] = $playlist;
                } else {
                    preg_match_all( '#ids=([\'"])(.+?)\1#is', $playlist, $ids, PREG_SET_ORDER );
                    if ( ! empty( $ids ) ) {
                        foreach ( $ids as $id ) {
                            $ids[] = $id[2];
                        }
                    }

                    $playlists[] = array_merge(
                        $shortcode_attrs,
                        array(
                            'ids' => array_values( array_unique( $ids ) )
                        )
                    );
                }
            }
        }
    }
    return $playlists;
}