hi wim and Jyoti  :     thank you for your replies .I followed your suggestions and rewrite the code.But it still can't  work fine.  I get the following error:     Running...     catch video in decodebin     Dynamic pad created, linking decoderbin/queue     catch audio in decodebin     Dynamic pad created, linking decoderbin/queue     Error: internal data flow error     Returned, stopping playback     Deleting pipeline please give me some more suggestion,i will thank you very much.     By the way,i find a source code on net, he didn't use callback.Instead ,he write the code as follow     send_rtp_sink0 = gst_element_get_request_pad(rtpbin, "send_rtp_sink_0");     send_rtp_src0 = gst_element_get_static_pad(rtpbin, "send_rtp_src_0"); and the reason is :in the Reference it's described that the "send_rtp_src_%d" pad is automatically created if a pad_request to "send_rtp_sink_%d" is called.     I have tried this method ,but failed. #include <gst/gst.h> #include <glibh> #include <unistd.h> #include <stdlib.h> // global declaration GstElement *pipeline,*udpsink0,*udpsink1; GstElement *audio_bin,*video_bin; // gboolean res;//element link GstPadLinkReturn lres;//pad link //bus 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 *error;       gst_message_parse_error (msg, &error, &debug);       g_free (debug);       g_printerr ("Error: %s\n", error->message);       g_error_free (error);       g_main_loop_quit (loop);       break;     }     default:       break;   }   return TRUE; } static void on_pad_added_rtpbin(GstElement *element, GstPad *pad, gpointer data) {     GstCaps *caps=NULL;     GstStructure *str=NULL;     GstPad *t_pad=NULL;         g_assert(pad!=NULL);     caps=gst_pad_get_caps(pad);     str=gst_caps_get_structure(caps,0);         //media type audio or video          if (g_strrstr (gst_structure_get_name (str), "audio"))          {                          g_print("rtp catch audio\n");             t_pad = gst_element_get_static_pad (udpsink0, "sink");             g_assert(t_pad!=NULL);                                    }          else if(g_strrstr (gst_structure_get_name (str), "video"))       {                    g_print("rtp catch video\n");             t_pad = gst_element_get_static_pad (udpsink1, "sink");             g_assert(t_pad!=NULL);                         }         else         {             gst_caps_unref (caps);             return;         }                 if (GST_PAD_IS_LINKED (t_pad))       {           gst_caps_unref (caps);             g_object_unref (t_pad);             return;       }       else       {                    lres=gst_pad_link (pad, t_pad);           g_assert (lres == GST_PAD_LINK_OK);           g_print("Dynamic pad created, linking rtpbin/udp\n");                               gst_caps_unref (caps);                      g_object_unref (t_pad);             return;       }         } static void on_pad_added_decodebin(GstElement *decodebin,GstPad *pad,gboolean last,gpointer data) {     GstCaps *caps;       GstStructure *str;       GstPad *t_pad;         //media type     caps = gst_pad_get_caps (pad);       str = gst_caps_get_structure (caps, 0);       //check media type audio or video          if (g_strrstr (gst_structure_get_name (str), "audio"))          {                          g_print("catch audio in decodebin\n");             t_pad = gst_element_get_static_pad (audio_bin, "sink");             g_assert(t_pad!=NULL);             if(t_pad==NULL)                 g_print("cannot get the sink pad of audiobin ");                        }          else if(g_strrstr (gst_structure_get_name (str), "video"))       {                    g_print("catch video in decodebin\n");             t_pad = gst_element_get_static_pad (video_bin, "sink");             g_assert(t_pad!=NULL);             if(t_pad==NULL)                 g_print("cannot get the sink pad of videobin ");                       }         else         {             gst_caps_unref (caps);             return;         }                       if (GST_PAD_IS_LINKED (t_pad))       {           gst_caps_unref (caps);             g_object_unref (t_pad);             return;       }             else       {                    gst_pad_link (pad, t_pad);           g_print("Dynamic pad created, linking decoderbin/queue\n");                     gst_caps_unref (caps);                      g_object_unref (t_pad);             return;       }         } int main(int argc, char **argv) {     GMainLoop *loop;     GstBus *bus;         //pad of rtpbin     GstPad *sink_pad;        GstPad *bin_pad;            GstPad *videopad_src,*videopad_sink;     GstPad *audiopad_src,*audiopad_sink;     //declare elements     GstElement  *filesrc,*decodebin,*gstrtpbin;     //element for video     GstElement *queue1,*x264enc,*rtph264pay;     //element for audio     GstElement *queue2,*audioresample,*audioconvert,*alawenc,*rtppcmapay;         gst_init(&argc, &argv);     loop = g_main_loop_new(NULL, FALSE);         //generate elements     pipeline = gst_pipeline_new("server");     filesrc=gst_element_factory_make("filesrc", "filesrc");     decodebin=gst_element_factory_make("decodebin", "decodebin");     gstrtpbin = gst_element_factory_make("gstrtpbin", "gstrtpbin");     //for video     queue1=gst_element_factory_make("queue", "queue1");     x264enc=gst_element_factory_make("x264enc", "x264enc");     rtph264pay=gst_element_factory_make("rtph264pay", "rtph264pay");     udpsink0=gst_element_factory_make("udpsink", "udpsink0");     //for audio     queue2 = gst_element_factory_make("queue", "queue2");     audioresample = gst_element_factory_make("audioresample", "audioresample");     audioconvert = gst_element_factory_make("audioconvert", "audioconvert");     alawenc = gst_element_factory_make("alawenc", "alawenc");        rtppcmapay = gst_element_factory_make("rtppcmapay", "rtppcmapay");     udpsink1=gst_element_factory_make("udpsink", "udpsink1");         bus = gst_pipeline_get_bus(GST_PIPELINE(pipeline));     gst_bus_add_watch(bus, bus_call, loop);     gst_object_unref(bus);         //set properties of elements     g_object_set(G_OBJECT(filesrc), "location","/home/xuxin/desktop/g_p/a.avi", NULL);        g_object_set(G_OBJECT(udpsink0), "port",5000, NULL);     g_object_set(G_OBJECT(udpsink1), "port",5002, NULL);     g_object_set(G_OBJECT(udpsink0), "host","172.21.29.169", NULL);     g_object_set(G_OBJECT(udpsink1), "host","172.21.29.169", NULL);     g_object_set(G_OBJECT(udpsink0), "sync",FALSE, NULL);     g_object_set(G_OBJECT(udpsink1), "sync",FALSE, NULL);         //create video_bin     video_bin = gst_bin_new ("videobin");     gst_bin_add_many (GST_BIN (video_bin),queue1,x264enc,rtph264pay,NULL);     res=gst_element_link_many(queue1,x264enc,rtph264pay,NULL);     g_assert (res == TRUE);     //add pad to video_bin     videopad_sink = gst_element_get_static_pad (queue1, "sink");     videopad_src= gst_element_get_static_pad (rtph264pay, "src");        gst_element_add_pad (video_bin,gst_ghost_pad_new ("sink", videopad_sink));     gst_element_add_pad (video_bin,gst_ghost_pad_new ("src",videopad_src));       gst_object_unref (videopad_sink);       gst_object_unref (videopad_src);             //create audio_bin       audio_bin = gst_bin_new ("audiobin");     gst_bin_add_many (GST_BIN (audio_bin),queue2,audioresample,audioconvert,alawenc,rtppcmapay,NULL);     res=gst_element_link_many(queue2,audioresample,audioconvert,alawenc,rtppcmapay,NULL);     g_assert (res == TRUE);     //add pad to audio_bin     audiopad_sink = gst_element_get_static_pad (queue2, "sink");     audiopad_src= gst_element_get_static_pad (rtppcmapay, "src");        res=gst_element_add_pad (audio_bin,gst_ghost_pad_new ("sink", audiopad_sink));     g_assert (res == TRUE);     res=gst_element_add_pad (audio_bin,gst_ghost_pad_new ("src", audiopad_src));     g_assert (res == TRUE);       gst_object_unref (audiopad_sink);       gst_object_unref (audiopad_src);         //add elements into pipeline     gst_bin_add_many(GST_BIN(pipeline),             filesrc,decodebin,audio_bin,video_bin,gstrtpbin,udpsink0,udpsink1,NULL);         //static link filesrc and decoderbin     res=gst_element_link(filesrc,decodebin);        g_assert (res == TRUE);            //get request pad from gstrtpbin and connect with video_bin     bin_pad=gst_element_get_pad(video_bin, "src");     g_assert(bin_pad!=NULL);        sink_pad = gst_element_get_request_pad(gstrtpbin, "recv_rtp_sink_0");     g_assert(sink_pad!=NULL);        lres=gst_pad_link(bin_pad, sink_pad);     g_assert (lres == GST_PAD_LINK_OK);             //get request pad from gstrtpbin and connect with audio_bin     bin_pad=gst_element_get_pad(audio_bin, "src");     g_assert(bin_pad!=NULL);     sink_pad = gst_element_get_request_pad(gstrtpbin, "recv_rtp_sink_1");     g_assert(sink_pad!=NULL);     lres=gst_pad_link(bin_pad, sink_pad);     g_assert (lres == GST_PAD_LINK_OK);     //signal link     g_signal_connect(decodebin, "new-decoded-pad", G_CALLBACK(on_pad_added_decodebin),NULL);            g_signal_connect(gstrtpbin, "pad-added", G_CALLBACK(on_pad_added_rtpbin),NULL);            gst_element_set_state(pipeline, GST_STATE_PLAYING);         g_print("Running...\n");     g_main_loop_run(loop);         /* Out of the main 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; }  <hr/> <a href="http://qiye.163.com/?ft=1">ҵ�񶩵��ʧ��ô�죿</a>