gstreamer code for playing avi file is hanging

Question

I am new to gstremaer. I have written a code for playing avi file using gstreamer. But on executing the code it just hangs after a while, I am unable to debug whats the problem, Can someone help me please. The code and the output is as below:

    Code:

    #include<stdio.h>
    #include<gst/gst.h>
    #include<glib.h>

    //Function to process message on bus of pipeline
    gboolean process_message(GstBus *bus, GstMessage *msg,gpointer data);

    //Function to add pad dynamically for ogg demux
void dynamic_addpad(GstElement *element, GstPad *pad, gpointer data);        
void dynamic_decodepad (GstElement* object, GstPad* arg0, gboolean arg1,gpointer user_data);

     GstElement *source, *demuxer, *audio_decoder, *video_decoder, *audio_convertor,*video_convertor, *audio_sink,*video_sink,*audioqueue,*videoqueue;//*audio_demuxer, *video_demuxer,

    int main(int argc,char* argv[])
    {

      GstPipeline *pipeline;
      GstBin *Bin;
      GstBus *bus;
      GMainLoop *Mainloop;

      gst_init (&argc,&argv);

      Mainloop = g_main_loop_new(NULL,FALSE);//NULL to use the current context and False to tell its not in running state

      pipeline = gst_pipeline_new("PIPELINE");
      Bin = GST_BIN(pipeline);
      bus = gst_pipeline_get_bus(pipeline);


      source = gst_element_factory_make("filesrc","file-source");
      g_object_set(G_OBJECT(source),"location",argv[1],NULL);

      demuxer = gst_element_factory_make("avidemux","avi-demuxer");
      audioqueue = gst_element_factory_make("queue","Queue for audio");
      videoqueue = gst_element_factory_make("queue","Queue for video");
      video_decoder = gst_element_factory_make("decodebin","decoderbin");//"Vorbis audio decoder","vorbis");
      audio_convertor = gst_element_factory_make("audioconvert","audio convertor");//"Audio converter","audioconvert");
      video_convertor = gst_element_factory_make("videoscale","video convertor");//"Audio converter","audioconvert");
      audio_sink = gst_element_factory_make("autoaudiosink","Auto audio sink");
      video_sink = gst_element_factory_make("xvimagesink","XV video sink ");

      if(!source || !demuxer || !audioqueue || !videoqueue || !video_decoder ||!audio_convertor || !video_convertor || !audio_sink || !video_sink  )
      {   g_print("Could not not create element\n");
        return 0;
      }
      gst_bin_add(Bin,source);
      gst_bin_add_many(Bin,demuxer,audioqueue,videoqueue,audio_convertor,video_decoder,video_convertor,audio_sink,video_sink,NULL);

      gst_element_link(source,demuxer);
      gst_element_link_many(audioqueue,video_decoder,audio_convertor,audio_sink,NULL);
      gst_element_link_many(videoqueue,video_decoder,video_convertor,video_sink,NULL);

      g_signal_connect(demuxer,"pad-added",G_CALLBACK(dynamic_addpad),NULL);//demuxer and decoder are passed as instance and data as pads of both the elements are linked in dynamic_addpad
      g_signal_connect(video_decoder,"new-decoded-pad",G_CALLBACK(dynamic_decodepad),NULL);//demuxer and decoder are passed as instance and data as pads of both the elements are linked in dynamic_addpad
      gst_bus_add_watch(bus,process_message,Mainloop); //Mainloop is passed as user data as in the process_message actions are taken on the loop
      g_object_unref(bus);
      g_print("In playing state\n");
      gst_element_set_state(pipeline,GST_STATE_PLAYING);//Pipeline is also a bin and bin is also an element at abstract level and hence gst_element_set_state call is used to set state of pipeline.

      g_main_loop_run(Mainloop);
      g_print("In playing state2\n");
      gst_element_set_state(pipeline,GST_STATE_NULL);
      g_object_unref(G_OBJECT(pipeline));
    }



    //Function to process message on bus of pipeline
    gboolean process_message(GstBus *bus, GstMessage *msg,gpointer data)
    {
      GError *error;
      gchar *debug;
      GMainLoop *loop = (GMainLoop *)data;

      g_print(" In process message msg->type : %d\n",GST_MESSAGE_TYPE(msg));
      switch(GST_MESSAGE_TYPE(msg))
      {
        case   GST_MESSAGE_UNKNOWN :
                g_print("GST_MESSAGE_UNKNOWN \n");
                break;
        case   GST_MESSAGE_EOS     :
                g_print("GST_MESSAGE_EOS \n");
                g_main_loop_quit(loop);
                break;
        case   GST_MESSAGE_ERROR   :
                g_print("GST_MESSAGE_ERROR \n");
                gst_message_parse_error (msg, &error, &debug);
                g_free(debug);
                //if(!error)
                {
                  g_print("GST_MESSAGE_ERROR message : %s \n",error->message);
                }
                g_main_loop_quit(loop);
                break;
        case   GST_MESSAGE_WARNING :
                g_print("GST_MESSAGE_WARNING  \n");
                break;
        case   GST_MESSAGE_INFO    :
                g_print("GST_MESSAGE_INFO \n");
                break;
        case   GST_MESSAGE_TAG     :
                g_print("GST_MESSAGE_TAG \n");
                break;
        case   GST_MESSAGE_BUFFERING:
                g_print("GST_MESSAGE_BUFFERING \n");
                break;
        case   GST_MESSAGE_STATE_CHANGED:
                g_print("GST_MESSAGE_STATE_CHANGED \n");
                break;
        default : 
                g_print("default \n");
                break;

      }
      return TRUE; //returns true always as it has to be always registered returning false will deregister the function
    }

    //Function to add pad dynamically for ogg demux
    void dynamic_addpad(GstElement *element, GstPad *pad, gpointer data)
    {
      GstPad *audiodemuxsink;
      GstPad *videodemuxsink;
      GstElement *decoder = (GstElement *)data;
      g_print(" In dynamic ADDING PAD\n");

      audiodemuxsink = gst_element_get_static_pad(audioqueue,"sink");
      gst_pad_link(pad,audiodemuxsink );
      videodemuxsink = gst_element_get_static_pad(videoqueue,"sink");
      gst_pad_link(pad,videodemuxsink );
      g_print(" In dynamic ADDING PAD2\n");

    }



    void dynamic_decodepad (GstElement* object, GstPad* pad, gboolean arg1,gpointer user_data)
    {
      GstPad *videoconvertsink;
      GstPad *audioconvertsink ;
      g_print(" In dynamic_decodepad ADDING PAD\n");

      videoconvertsink = gst_element_get_static_pad(video_convertor,"sink");
      gst_pad_link(pad,videoconvertsink);
      audioconvertsink  = gst_element_get_static_pad(audio_convertor,"sink");
      gst_pad_link(pad,audioconvertsink  );
      g_print(" In dynamic_decodepad ADDING PAD2\n");

    }


    Output:
    In playing state
     In process message msg->type : 64
    GST_MESSAGE_STATE_CHANGED 
     In process message msg->type : 64
    GST_MESSAGE_STATE_CHANGED 
     In process message msg->type : 64
    GST_MESSAGE_STATE_CHANGED 
     In process message msg->type : 64
    GST_MESSAGE_STATE_CHANGED 
     In process message msg->type : 64
    GST_MESSAGE_STATE_CHANGED 
     In process message msg->type : 64
    GST_MESSAGE_STATE_CHANGED 
     In process message msg->type : 64
    GST_MESSAGE_STATE_CHANGED 
     In process message msg->type : 64
    GST_MESSAGE_STATE_CHANGED 
     In process message msg->type : 64
    GST_MESSAGE_STATE_CHANGED 
     In process message msg->type : 64
    GST_MESSAGE_STATE_CHANGED 
     In process message msg->type : 64
    GST_MESSAGE_STATE_CHANGED 
     In process message msg->type : 64
    GST_MESSAGE_STATE_CHANGED 
     In process message msg->type : 64
    GST_MESSAGE_STATE_CHANGED 
     In process message msg->type : 64
    GST_MESSAGE_STATE_CHANGED 
     In process message msg->type : 8192
    default 
     In process message msg->type : 64
    GST_MESSAGE_STATE_CHANGED 
     In process message msg->type : 64
    GST_MESSAGE_STATE_CHANGED 
     In process message msg->type : 64
    GST_MESSAGE_STATE_CHANGED 
     In process message msg->type : 8192
    default 
     In process message msg->type : 64
    GST_MESSAGE_STATE_CHANGED 
     In process message msg->type : 64
    GST_MESSAGE_STATE_CHANGED 
     In process message msg->type : 8192
    default 
     In process message msg->type : 8192
    default 
     In dynamic ADDING PAD
     In dynamic ADDING PAD2
     In dynamic ADDING PAD
     In dynamic ADDING PAD2
     In process message msg->type : 16
    GST_MESSAGE_TAG 
     In process message msg->type : 16
    GST_MESSAGE_TAG 
     In process message msg->type : 16
    GST_MESSAGE_TAG 
     In process message msg->type : 64
    GST_MESSAGE_STATE_CHANGED 
     In dynamic_decodepad ADDING PAD
     In dynamic_decodepad ADDING PAD2
     In process message msg->type : 64
    GST_MESSAGE_STATE_CHANGED 
     In process message msg->type : 64
    GST_MESSAGE_STATE_CHANGED 
     In process message msg->type : 64
    GST_MESSAGE_STATE_CHANGED 
     In process message msg->type : 64
    GST_MESSAGE_STATE_CHANGED 
     In process message msg->type : 64
    GST_MESSAGE_STATE_CHANGED 

It hangs at this point. Any help is appreciated. Thanks in advance.

Answer 1

Your code is wrong in several ways, that is why my answer is so long.

First of all, gst_pipeline_new returns GstElement* not GstPipeline*:

-  pipeline = gst_pipeline_new("PIPELINE");
+  GstElement *pipeline = gst_pipeline_new("PIPELINE");
   Bin = GST_BIN(pipeline);
-  bus = gst_pipeline_get_bus(pipeline);
+  bus = gst_pipeline_get_bus(GST_PIPELINE(pipeline));

Then, your pipeline is wrong: you trying to decode both streams (audio and video) with one decodebin but you need two. Create it and don't forget to add it to the bin:

   videoqueue = gst_element_factory_make("queue","Queue for video");
+  audio_decoder = gst_element_factory_make("decodebin","a_decodebin");
   video_decoder = gst_element_factory_make("decodebin","decoderbin");//"Vorbis audio decoder","vorbis");

-  gst_bin_add_many(Bin,demuxer,audioqueue,videoqueue,audio_convertor,video_decoder,video_convertor,audio_sink,video_sink,NULL);
+  gst_bin_add_many(
+    Bin,
+    demuxer,
+    audioqueue,videoqueue,
+    audio_decoder,audio_convertor,
+    video_decoder,video_convertor,
+    audio_sink,video_sink,
+    NULL);

And, by the way, it's better to use decodebin2 as decodebin is deprecated.

Then you linking some elements dynamically: demuxer to queue and decodebin to convertors. Hence you should not create link between decodebin and convertors with gst_element_link_many:

   gst_element_link(source,demuxer);
-  gst_element_link_many(audioqueue,video_decoder,audio_convertor,audio_sink,NULL);
-  gst_element_link_many(videoqueue,video_decoder,video_convertor,video_sink,NULL);
+  gst_element_link_many(audioqueue,audio_decoder,NULL);
+  gst_element_link_many(audio_convertor,audio_sink,NULL);
+  gst_element_link_many(videoqueue,video_decoder,NULL);
+  gst_element_link_many(video_convertor,video_sink,NULL);

And of course, as we added audio_decoder decodebin, we need to handle it's pad creation signal:

+  g_signal_connect(audio_decoder,"new-decoded-pad",G_CALLBACK(dynamic_decodepad),NULL);
   g_signal_connect(video_decoder,"new-decoded-pad",G_CALLBACK(dynamic_decodepad),NULL);

And now we are at the most interesting part.

void dynamic_addpad(GstElement *element, GstPad *pad, gpointer data)
{
  GstPad *audiodemuxsink;
  GstPad *videodemuxsink;
  GstElement *decoder = (GstElement *)data;
  g_print(" In dynamic ADDING PAD\n");

  audiodemuxsink = gst_element_get_static_pad(audioqueue,"sink");
  gst_pad_link(pad,audiodemuxsink );
  videodemuxsink = gst_element_get_static_pad(videoqueue,"sink");
  gst_pad_link(pad,videodemuxsink );
  g_print(" In dynamic ADDING PAD2\n");
}

This is completely wrong! dynamic_addpad is called on each pad creation. avidemux commonly creates two pads (one for each data stream): "audio_00" and "video_00". So, dynamic_addpad will be called twice and we need to distinguish what to link depending on pad name:

void dynamic_addpad(GstElement *element, GstPad *pad, gpointer data)
{
  char* pad_name = gst_pad_get_name(pad);
  g_print(" In dynamic ADDING PAD %s\n", pad_name);

  if (g_str_has_prefix(pad_name,"audio")) {
    GstPad *audiodemuxsink = gst_element_get_static_pad(audioqueue,"sink");
    gst_pad_link(pad,audiodemuxsink );
  }
  else if (g_str_has_prefix(pad_name,"video")) {
    GstPad *videodemuxsink = gst_element_get_static_pad(videoqueue,"sink");
    gst_pad_link(pad,videodemuxsink );
  }
  g_free (pad_name);
}

Almost the same is for dynamic_decodepad. As it's only one src pad is created by decodebin, it will be easier to create separate handlers for video_decoder and audio_decoder.
But for pedagogical reasons I will do it in one function. Now we can distinguish which element to connect to pad by it's caps.

void dynamic_decodepad (GstElement* object, GstPad* pad, gboolean arg1,gpointer user_data)
{
  GstPad* videoconvertsink = gst_element_get_static_pad(video_convertor,"sink");
  if (gst_pad_can_link(pad,videoconvertsink)) {
    gst_pad_link(pad,videoconvertsink);
  }

  GstPad* audioconvertsink  = gst_element_get_static_pad(audio_convertor,"sink");
  if (gst_pad_can_link(pad,audioconvertsink)) {
    gst_pad_link(pad,audioconvertsink);
  }
}

gst_pad_can_link will not work in dynamic_addpath because it's possible to connect query element both to "audio_00" and "video_00".

That's it. Don't hesitate to ask if you have other questions.