type specific data, check the type
field to know the
datatype. This field can be %NULL.
the id of the probe
offset of pull probe, this field is valid when type
contains
#GST_PAD_PROBE_TYPE_PULL
size of pull probe, this field is valid when type
contains
#GST_PAD_PROBE_TYPE_PULL
the current probe type
Info passed in the #GstPadProbeCallback.