The code is very simple, a playbin2, with an uri, and the next uri is set in the about-to-finish signal. void about_to_finish_cb (GstElement * element, gpointer * uri) { gchar* uri2 = (gchar*)uri; g_object_set (G_OBJECT (element), "uri",uri2, NULL); } I tested it by hardcoding also: g_object_set (G_OBJECT (element), "uri","file:///home/videos/video1.avi", NULL); It didn't work either. Here is the code where I do the callback in the main, the whole code is very straight forward, so I think the problem is how I call the about-to-finish event. char uri_next[] = "file:///home/videos/video11.avi"; g_signal_connect (play, "about-to-finish", G_CALLBACK (about_to_finish_cb),uri_next); gst_element_set_state (play, GST_STATE_PLAYING); The error appears in the about_to_finish_cb function, when I try to set the new uri: GLib-GObject-CRITICAL **: g_object_set: assertion `G_IS_OBJECT (object)' failed I checked the mailing list but none of the examples suits mine. Thank you. Rossana