Hello everyone ! I'm trying to develop an image-processing application for the nokia N810 using gstreamer. I have made the structure of this application using an example which display the image of the camera on the screen. I tweaked a bit this code for my need, and it is working, I can actually display the picture from the camera, start/stop the media pipeline... But I don't find where to put the image processing code (which is working alone on the nokia). What I want is that when the program receive a frame from the camera, it has to do some calculation with the current frame buffer, and during these calculations, I'd like it to ignore the other frame coming from the camera. (I don't think that the processor will be able to handle realtime processing). When the calculation is done, it should start again with the next coming frame. I managed to do it, but I had to press a button each time I wanted to process a frame. I'd like the program to do it continuously. Here is my code : #define VIDEO_SRC "v4l2src" #define VIDEO_SINK "xvimagesink" typedef struct {     HildonProgram *program;     HildonWindow *window;     GstElement *pipeline;     GtkWidget *screen;         guint buffer_cb_id; } AppData; /* Callback that gets called when user clicks the "START/STOP" button */ static void button1_pressed(GtkWidget *widget,AppData *appdata) {     if (GTK_TOGGLE_BUTTON(widget)->active)         {         /* Display a note to the user */         hildon_banner_show_information(GTK_WIDGET(appdata->window),                         NULL, "Running ...");         gst_element_set_state(appdata->pipeline, GST_STATE_PLAYING);         }     else         {         /* Display a note to the user */         hildon_banner_show_information(GTK_WIDGET(appdata->window),                         NULL, "Stopped ...");         gst_element_set_state(appdata->pipeline, GST_STATE_PAUSED);                        } } /* Callback that gets called when user clicks the "Expression ON/OFF" button */ static void button2_pressed(GtkWidget *widget, AppData *appdata) {     if (GTK_TOGGLE_BUTTON(widget)->active)         {                 /* Display a note to the user */         hildon_banner_show_information(GTK_WIDGET(appdata->window),                         NULL, "Expressions ON");         }     else         {         /* Display a note to the user */         hildon_banner_show_information(GTK_WIDGET(appdata->window),                         NULL, "Expressions OFF");         } } /* Callback that gets called whenever pipeline's message bus has  * a message */ static void bus_callback(GstBus *bus, GstMessage *message, AppData *appdata) {     gchar *message_str;     const gchar *message_name;     GError *error;         /* Report errors to the console */     if(GST_MESSAGE_TYPE(message) == GST_MESSAGE_ERROR)     {            gst_message_parse_error(message, &error, &message_str);         g_error("GST error: %s\n", message_str);         g_free(error);         g_free(message_str);     }         /* Report warnings to the console */     if(GST_MESSAGE_TYPE(message) == GST_MESSAGE_WARNING)     {            gst_message_parse_warning(message, &error, &message_str);         g_warning("GST warning: %s\n", message_str);         g_free(error);         g_free(message_str);     }     /* See if the message type is GST_MESSAGE_APPLICATION which means      * thet the message is sent by the client code (this program) and      * not by gstreamer. */     if(GST_MESSAGE_TYPE(message) == GST_MESSAGE_APPLICATION)     {         /* Get name of the message's structure */         message_name = gst_structure_get_name(gst_message_get_structure(message));                 /* The hildon banner must be shown in here, because the bus callback is          * called in the main thread and calling GUI-functions in gstreamer threads          * usually leads to problems with X-server */                 if(!strcmp(message_name, "anger"))         {             hildon_banner_show_information(                     GTK_WIDGET(appdata->window),                     NULL, "Anger");         }                 if(!strcmp(message_name, "disgust"))         {             hildon_banner_show_information(                     GTK_WIDGET(appdata->window),                     NULL, "Disgust");         }         if(!strcmp(message_name, "fear"))         {             hildon_banner_show_information(                     GTK_WIDGET(appdata->window),                     NULL, "Fear");         }         if(!strcmp(message_name, "happy"))         {             hildon_banner_show_information(                     GTK_WIDGET(appdata->window),                     NULL, "Happy");         }         if(!strcmp(message_name, "neutral"))         {             hildon_banner_show_information(                     GTK_WIDGET(appdata->window),                     NULL, "Neutral");         }         if(!strcmp(message_name, "sad"))         {             hildon_banner_show_information(                     GTK_WIDGET(appdata->window),                     NULL, "Sad");         }         if(!strcmp(message_name, "surprise"))         {             hildon_banner_show_information(                     GTK_WIDGET(appdata->window),                     NULL, "Surprise");         }         if(!strcmp(message_name, "unknown"))         {             hildon_banner_show_information(                     GTK_WIDGET(appdata->window),                     NULL, "Unknown !");         }     }             } /* Callback to be called when the screen-widget is exposed */ static gboolean expose_cb(GtkWidget * widget, GdkEventExpose * event, gpointer data) {     /* Tell the xvimagesink/ximagesink the x-window-id of the screen      * widget in which the video is shown. After this the video      * is shown in the correct widget */     gst_x_overlay_set_xwindow_id(GST_X_OVERLAY(data),                      GDK_WINDOW_XWINDOW(widget->window));     return FALSE; } /* Initialize the the Gstreamer pipeline. Below is a diagram  * of the pipeline that will be created:  *  *                              *                           -  * |Camera|  |CSP   |  |Screen|  |Screen|   |Image     |  * |src   |->|Filter|->|queue |->|sink  |-> |processing|->  Display  */ static gboolean initialize_pipeline(AppData *appdata,         int *argc, char ***argv) {     GstElement *pipeline, *camera_src, *screen_sink;     GstElement *screen_queue;     GstElement *csp_filter;     GstCaps *caps;     GstBus *bus;     /* Initialize Gstreamer */     gst_init(argc, argv);         /* Create pipeline and attach a callback to it's      * message bus */     pipeline = gst_pipeline_new("test-camera");     bus = gst_pipeline_get_bus(GST_PIPELINE(pipeline));     gst_bus_add_watch(bus, (GstBusFunc)bus_callback, appdata);     gst_object_unref(GST_OBJECT(bus));         /* Save pipeline to the AppData structure */     appdata->pipeline = pipeline;         /* Create elements */     /* Camera video stream comes from a Video4Linux driver */     camera_src = gst_element_factory_make(VIDEO_SRC, "camera_src");     /* Colorspace filter is needed to make sure that sinks understands      * the stream coming from the camera */     csp_filter = gst_element_factory_make("ffmpegcolorspace", "csp_filter");     /* Queue creates new thread for the stream */     screen_queue = gst_element_factory_make("queue", "screen_queue");     /* Sink that shows the image on screen. Xephyr doesn't support XVideo      * extension, so it needs to use ximagesink, but the device uses      * xvimagesink */     screen_sink = gst_element_factory_make(VIDEO_SINK, "screen_sink");     /* Check that elements are correctly initialized */     if(!(pipeline && camera_src && screen_sink && csp_filter && screen_queue))     {         g_critical("Couldn't create pipeline elements");         return FALSE;     }         /* Add elements to the pipeline. This has to be done prior to      * linking them */     gst_bin_add_many(GST_BIN(pipeline), camera_src, csp_filter,             screen_queue, screen_sink, NULL);         /* Specify what kind of video is wanted from the camera */     caps = gst_caps_new_simple("video/x-raw-rgb",             "width", G_TYPE_INT, 640,             "height", G_TYPE_INT, 480,             "framerate", GST_TYPE_FRACTION, 25, 1,             NULL);                 /* Link the camera source and colorspace filter using capabilities      * specified */     if(!gst_element_link_filtered(camera_src, csp_filter, caps))     {         return FALSE;     }     gst_caps_unref(caps);         /* Connect Colorspace Filter -> Screen Queue -> Screen Sink      * This finalizes the initialization of the screen-part of the pipeline */     if(!gst_element_link_many(csp_filter, screen_queue, screen_sink, NULL))     {         return FALSE;     }     /* As soon as screen is exposed, window ID will be advised to the sink */     g_signal_connect(appdata->screen, "expose-event", G_CALLBACK(expose_cb),              screen_sink);         gst_element_set_state(pipeline, GST_STATE_PAUSED);        return TRUE; } /* Destroy the pipeline on exit */ static void destroy_pipeline(GtkWidget *widget, AppData *appdata) {     /* Free the pipeline. This automatically also unrefs all elements      * added to the pipeline */     gst_element_set_state(appdata->pipeline, GST_STATE_NULL);     gst_object_unref(GST_OBJECT(appdata->pipeline)); } int main(int argc, char **argv) { // variables for face detection     // main structure for vjdetect     pdata = (mainstruct*) calloc(1, sizeof(mainstruct));     // Allocate memory for array of face detections returned by facedetector (VjDetect).     pdata->pFaceDetections = (FLY_Rect *)calloc(MAX_NUMBER_OF_FACE_DETECTIONS, sizeof(FLY_Rect));     init(pdata);     AppData appdata;     GtkWidget *hbox, *vbox_button, *vbox, *button1, *button2;     /* Initialize and create the GUI */         example_gui_initialize(         &appdata.program, &appdata.window,         &argc, &argv, "Expression Detector");     vbox = gtk_vbox_new(FALSE, 0);     hbox = gtk_hbox_new(FALSE, 0);     vbox_button = gtk_vbox_new(FALSE, 0);     gtk_box_pack_start(GTK_BOX(hbox), vbox, FALSE, FALSE, 0);     gtk_box_pack_start(GTK_BOX(hbox), vbox_button, FALSE, FALSE, 0);     appdata.screen = gtk_drawing_area_new();     gtk_widget_set_size_request(appdata.screen, 500, 380);     gtk_box_pack_start(GTK_BOX(vbox), appdata.screen, FALSE, FALSE, 0);     button1 = gtk_toggle_button_new_with_label("Run/Stop");     gtk_widget_set_size_request(button1, 170, 75);     gtk_box_pack_start(GTK_BOX(vbox_button), button1, FALSE, FALSE, 0);     button2 = gtk_toggle_button_new_with_label("Expressions ON/OFF");     gtk_widget_set_size_request(button2, 170, 75);     gtk_box_pack_start(GTK_BOX(vbox_button), button2, FALSE, FALSE, 0);     g_signal_connect(G_OBJECT(button1), "clicked",              G_CALLBACK(button1_pressed), &appdata);     g_signal_connect(G_OBJECT(button2), "clicked",              G_CALLBACK(button2_pressed), &appdata);     gtk_container_add(GTK_CONTAINER(appdata.window), hbox);     /* Initialize the GTK pipeline */     if(!initialize_pipeline(&appdata, &argc, &argv))     {         hildon_banner_show_information(                 GTK_WIDGET(appdata.window),                 "gtk-dialog-error",                 "Failed to initialize pipeline");     }     g_signal_connect(G_OBJECT(appdata.window), "destroy",             G_CALLBACK(destroy_pipeline), &appdata);     /* Begin the main application */     example_gui_run(appdata.program, appdata.window);     /* Free the gstreamer resources. Elements added      * to the pipeline will be freed automatically */         return 0; } I removed the image processing functions to have a better clarity. I tried to put a printf in the exposecb functions, in the main and in the pipeline, with the hope that it will display the text each time a new frame is displayed on the screen. That didn't work, it appears only once. I read tutorials about gstreamer but couldn't find how to do something continously. Maybe I should write a image_processing callback, and put in my main a g_signal_connect call that start this callback each time a new frame is displayed ? But what would be the correct signal to use ? Any idea welcome. Thanks in advance ! Bruno