Message.parseStateChanged

Extracts the old and new states from the GstMessage.

Typical usage of this function might be:

...
switch (GST_MESSAGE_TYPE (msg)) {
case GST_MESSAGE_STATE_CHANGED: {
GstState old_state, new_state;

gst_message_parse_state_changed (msg, &old_state, &new_state, NULL);
g_print ("Element `s` changed state from `s` to `s`.\n",
GST_OBJECT_NAME (msg->src),
gst_element_state_get_name (old_state),
gst_element_state_get_name (new_state));
break;
}
...
}
...

MT safe.