How to use videomixer element for gstreamer? - gstreamer

Question

I want to play two local video file using gstreamer,but I got an error: Segmentation fault It from libgstvideomixer.so.What's wrong with my code? The videomixer element is needed to play two videos.Should I use videobox for that?
gst-launch --no-fault filesrc location=/mnt/upan/source.264 ! queue ! typefind ! ffdec_h264 ! videomixer name=mix ! xvimagesink sync=false filesrc location=/mnt/upan/source.264 ! queue ! typefind ! ffdec_h264! mix.
static void p_gst_init(void)
{
App *app = &s_app;
GError *error = NULL;
GstBus *bus;
GstElement *parse, *decoder, *queue;
GstElement *parse2, *decoder2, *queue2;
gst_init (NULL, NULL);
/* create a mainloop to get messages */
app->loop = g_main_loop_new (NULL, TRUE);
app->playbin = gst_pipeline_new ("pipeline");
app->appsrc = gst_element_factory_make ("filesrc", "disk_source");
g_object_set (G_OBJECT (app->appsrc), "location", "/mnt/upan/test.264", NULL);
queue = gst_element_factory_make ("queue", "queue");
parse = gst_element_factory_make ("typefind", "parse");
decoder = gst_element_factory_make ("ffdec_h264", "decoder");
GstElement *filesrc2;
filesrc2 = gst_element_factory_make ("filesrc", "disk_source2");
g_object_set (G_OBJECT (appsrc2), "location", "/mnt/upan/source.264", NULL);
queue2 = gst_element_factory_make ("queue", "queue2");
parse2 = gst_element_factory_make ("typefind", "parse2");
decoder2 = gst_element_factory_make ("ffdec_h264", "decoder2");
/*
GstElement * videobox;
videobox = gst_element_factory_make("videobox", NULL);
g_object_set (videobox, "alpha", 0, "border-alpha", 0, "bottom", 100, "left", 100, "right", 100, "top", 100, NULL);
*/
GstElement * videomixer;
videomixer = gst_element_factory_make("videomixer","videomixer");
app->xvimagesink = gst_element_factory_make ("xvimagesink", "play_video");
g_object_set (G_OBJECT (app->xvimagesink), "synchronous", FALSE, NULL);
gst_bin_add_many (GST_BIN (app->playbin), app->appsrc, queue, parse, decoder, videomixer, app->xvimagesink, filesrc2, queue2, parse2, decoder2, NULL);
if(gst_element_link_many (app->appsrc, queue, parse, decoder, videomixer, NULL))
{
printf("---------link element success-----------------\n");
}
else
printf("---------link element failed-----------------\n");
gst_element_link_many (filesrc2, queue2, parse2, decoder2, videomixer, NULL);
gst_element_link_many(videomixer, app->xvimagesink, NULL);
bus = gst_pipeline_get_bus (GST_PIPELINE (app->playbin));
gst_bus_add_watch (bus, (GstBusFunc) bus_message, app);
gst_bus_set_sync_handler(bus, (GstBusSyncHandler)create_window, app);
g_signal_connect (app->appsrc, "need-data", G_CALLBACK (feed_data), app);
return ;
}