the probe mask
#GstPadProbeCallback that will be called with notifications of the pad state
user data passed to the callback
#GDestroyNotify for user_data
Return: an id or 0 if no probe is pending. The id can be used to remove the probe with gst_pad_remove_probe(). When using GST_PAD_PROBE_TYPE_IDLE it can happend that the probe can be run immediately and if the probe returns GST_PAD_PROBE_REMOVE this functions returns 0.
MT safe.
Be notified of different states of pads. The provided callback is called for every state that matches @mask.