Hello all My name is Corentin and I'm working on a web multimedia project based on Django frameworkand Gstreamer, and I want to add a scene change detection fonctionality to my project. To do this i need to acces to the video data so I take a (long..) look at Gstreamer manual and made this code. It's made with the Hello world code to read a ogg audio file (Chapter 10 in the manual), I easily turned to play ogg video file and with the code from the example of data probing (Chapter 18 in the manual) so here is my code : #include <gst/gst.h> /* * Global objects are usually a bad thing. For the purpose of this * example, we will use them, however. */ GstElement *pipeline, *source, *parser, *decoder, *csp, *filter, *sink; static gboolean bus_call (GstBus *bus, GstMessage *msg, gpointer data) { GMainLoop *loop = (GMainLoop *) data; switch (GST_MESSAGE_TYPE (msg)) { case GST_MESSAGE_EOS: g_print ("End-of-stream\n"); g_main_loop_quit (loop); break; case GST_MESSAGE_ERROR: { gchar *debug; GError *err; gst_message_parse_error (msg, &err, &debug); g_free (debug); g_print ("Error: %s\n", err->message); g_error_free (err); g_main_loop_quit (loop); break; } default: break; } return TRUE; } // this fonction deals with the pixels (it should invert the video) static gboolean cb_have_data (GstPad *pad, GstBuffer *buffer, gpointer u_data) { g_print ("Youpi, you are in the loop of the frame \n"); gint x, y; guint16 *data = (guint16 *) GST_BUFFER_DATA (buffer), t; // invert data for (y = 0; y < 288; y++) { for (x = 0; x < 384 / 2; x++) { t = data[384 - 1 - x]; data[384 - 1 - x] = data[x]; data[x] = t; } data += 384; } return TRUE; } // add a pad static void new_pad (GstElement *element, GstPad *pad, gpointer data) { GstPad *sinkpad;/* We can now link this pad with the audio decoder */ g_print ("Dynamic pad created, linking parser/decoder\n"); sinkpad = gst_element_get_pad (decoder, "sink"); gst_pad_link (pad, sinkpad); gst_object_unref (sinkpad); } int main (int argc, char *argv[]) { GMainLoop *loop; GstBus *bus; GstCaps *filtercaps; GstPad *pad2; /* initialize GStreamer */ gst_init (&argc, &argv); loop = g_main_loop_new (NULL, FALSE); /* check input arguments */ if (argc != 2) { g_print ("Usage: %s <Ogg/Vorbis filename>\n", argv[0]); return -1; } /* create elements */ pipeline = gst_pipeline_new ("player"); source = gst_element_factory_make ("filesrc", "file-source"); parser = gst_element_factory_make ("oggdemux", "ogg-parser"); decoder = gst_element_factory_make ("theoradec", "theora-decoder"); filter = gst_element_factory_make ("capsfilter", "filter"); csp = gst_element_factory_make ("ffmpegcolorspace", "csp"); g_assert (filter != NULL); /* should always exist */ sink = gst_element_factory_make ("ximagesink", "sink"); if (!pipeline || !source || !parser || !decoder || !csp || !filter ||!sink) { g_print ("One element could not be created\n"); return -1; } /* set filename property on the file source. Also add a message * handler. */ g_object_set (G_OBJECT (source), "location", argv[1], NULL); bus = gst_pipeline_get_bus (GST_PIPELINE (pipeline)); gst_bus_add_watch (bus, bus_call, loop); gst_object_unref (bus); /* put all elements in a bin */ gst_bin_add_many (GST_BIN (pipeline), source, parser, decoder, csp,filter, sink, NULL); /* link together - note that we cannot link the parser and * decoder yet, becuse the parser uses dynamic pads. For that, * we set a pad-added signal handler. */ gst_element_link (source, parser); gst_element_link_many (decoder, csp , filter, sink, NULL); g_signal_connect (parser, "pad-added", G_CALLBACK (new_pad), NULL); // create the filter caps vvith the video caracteristics filtercaps = gst_caps_new_simple ("video/x-raw-rgb", "width", G_TYPE_INT, 288, "height", G_TYPE_INT, 208, "framerate", GST_TYPE_FRACTION, 30, 1, //"bpp", G_TYPE_INT, 16, //"depth", G_TYPE_INT, 16, // "endianness", G_TYPE_INT, G_BYTE_ORDER, NULL); g_print ("try to set the caps on the filter\n"); g_object_set (G_OBJECT (filter), "caps", filtercaps, NULL); gst_caps_unref (filtercaps); g_print ("try to get the pad\n"); pad2 = gst_element_get_pad (csp,"csp"); if ( pad2 == NULL ) { g_print ("could not get the pad\n"); } //pad2 = gst_element_get_pad (csp, "csp"); //add the probe g_print ("\n setting the probe"); gst_pad_add_buffer_probe (pad2, G_CALLBACK (cb_have_data), NULL); g_print ("\nprobe added\n"); gst_object_unref (pad2); /* Now set to playing and iterate. */ g_print ("Setting to PLAYING\n"); gst_element_set_state (pipeline, GST_STATE_PLAYING); g_print ("Running\n"); g_main_loop_run (loop); /* clean up nicely */ g_print ("Returned, stopping playback\n"); gst_element_set_state (pipeline, GST_STATE_NULL); g_print ("Deleting pipeline\n"); gst_object_unref (GST_OBJECT (pipeline)); return 0; } To my mind the error comes from getting the pad. I take a look about this and I tried all the functions : gst_element_get_static_pad() & gst_element_get_request_pad(). The fact is I set the filter after the csp (ffmpegcolorspace) because it think this is here I will find the video data. I tried to set the filter before but nothing changed. I can't find my error. If anyone of you knows where I'm wrong it would be very nice to tell me because i'm getting mad. You 'll find the little video I use to test my code at : <a href="http://corentino.fr/dl/vid.ogg" target="_blank" onclick="return top.js.OpenExtLink(window,event,this)">http://corentino.fr/dl/vid.ogg</a> you'll need it, because some video properties are set in hard, if you try my code ! : ) Thank you by advance, Sincerly Corentin