'Switch to using appsrc for getting audio to be played.
You *MUST* call :meth:`prepare_change` before calling this method.
:param caps: GStreamer caps string describing the audio format to
expect
:type caps: string
:param need_data: callback for when appsrc needs data
:type need_data: callable which takes data length hint in ms
:param enough_data: callback for when appsrc has enough data
:type enough_data: callable
:param seek_data: callback for when data from a new position is needed
to continue playback
:type seek_data: callable which takes time position in ms'

def set_appsrc(self, caps, need_data=None, enough_data=None, seek_data=None):

    self._appsrc.prepare(Gst.Caps.from_string(caps), need_data, enough_data, seek_data)
    uri = u'appsrc://'
    self._pending_uri = uri
    self._playbin.set_property(u'uri', uri)
