'Configure audio to use an about-to-finish callback.
This should be used to achieve gapless playback. For this to work the
callback *MUST* call :meth:`set_uri` with the new URI to play and
block until this call has been made. :meth:`prepare_change` is not
needed before :meth:`set_uri` in this one special case.
:param callable callback: Callback to run when we need the next URI.'

def set_about_to_finish_callback(self, callback):

    self._about_to_finish_callback = callback
