[Vala] GStreamer signal connection in Vala

[Thomas <thomas mair86 gmail com>]

Hi,

I am new to Vala. I am trying to develop a simple application using
Gstreamer and Vala, but I fail with the connection of signlas defined
within the Gstreamer Element cairoooverlay
(http://developer.gnome.org/gst-plugins-libs/unstable/gst-plugins-good-plugins-cairooverlay.html).
What i am Trying to do ist the following:

this.pipeline =  (Pipeline)Gst.parse_launch("... cairooverlay
name=overlay ...");
...
Element ov = this.pipeline.get_by_name("overlay");
ov.connect("caps_changed", this.caps_changed_cb);

The code compiles fine, but I get the runtime warning and the signal
is not connected.

GLib-GObject-WARNING **: g_object_connect: invalid signal spec "caps_changed"

What is standard way to connect to this signal with a proper callback
in Vala? The function to connect the signal from C is
g_signal_connect.

Cheers
Thomas