public function callbackValidAudioUrl($sUrl)
    {
        $sId = $this->blog_post_model->extractSpotifyId($sUrl);

        if (!empty($sId)) {

            return true;

        } else {

            $oFormValidation = Factory::service('FormValidation');
            $oFormValidation->set_message('callbackValidAudioUrl', 'Not a valid Spotify Track URL.');
            return false;
        }
    }