waitUrl. The 'waitUrl' attribute lets you specify a URL for music that plays before the conference has started. The URL may be a WAV or a RCML document that uses <Play> or <Say> for content. This attribute defaults to a selection of Creative Commons licensed background music, but you can replace it with your own music and messages. If the 'waitUrl' responds with RCML, calls.teleapi will only process <Play>, <Say>, and <Redirect> verbs. If you do not wish to play any music while waiting for the conference to start, specify an empty string (“”).