How to specify output container / resolution / bitrate in GES

Hi i found this example.

But creating this container_profile throws TypeError: constructor returned NULL

How could i export video to webm with specified resolution and bitrate?

    container_profile = \
        GstPbutils.EncodingContainerProfile.new("pitivi-profile",
                                                "Pitivi encoding profile",
                                                Gst.Caps("video/webm"),
                                                None)

    video_profile = GstPbutils.EncodingVideoProfile.new(Gst.Caps("video/x-vp8"),
                                                        None,
                                                        Gst.Caps("video/x-raw"),
                                                        0)