g_signal_connect“添加了键盘”不起作用

Question

I am trying learning how to use dynamic pads in gstreamer. So I tried to add pad-added signal so I can get a message once an element is created. However, I didn't get any message.

Here is the code:

#include <gst/gst.h>

static void
cb_new_pad (GstElement *element,
        GstPad     *pad,
        gpointer    data)
{
  gchar *name;

  name = gst_pad_get_name (pad);
  g_print ("A new pad %s was created\n", name);
  g_free (name);

  /* here, you would setup a new pad link for the newly created pad */

}
int
main (int   argc,
      char *argv[]) 
{
  GstElement *pipeline, *source, *demux;
  GMainLoop *loop;

  /* init */
  gst_init (&argc, &argv);
  /* create elements */
  pipeline = gst_pipeline_new ("my_pipeline");
  source = gst_element_factory_make ("filesrc", "source");
  g_object_set (source, "location", argv[1], NULL);
  demux = gst_element_factory_make ("oggdemux", "demuxer");

  /* put together a pipeline */
  gst_bin_add_many (GST_BIN (pipeline), source, demux, NULL);
  gst_element_link_pads (source, "src", demux, "sink");

  /* listen for newly created pads */
  g_signal_connect (demux, "pad-added", G_CALLBACK (cb_new_pad), NULL);

  /* start the pipeline */
  gst_element_set_state (GST_ELEMENT (pipeline), GST_STATE_PLAYING);
  loop = g_main_loop_new (NULL, FALSE);
  g_main_loop_run (loop);

}

So what is the problem ? (By the way I am using gstreamer 1.2.1

Answer 1

Your code worked fine for me.

Your demuxer probably could not demultiplex the stream, check the input file that you are providing. It is probably not a valid ogg file.

On a related note, do add debugging code to your program ie listen to the bus for messages. It helps a lot when something doesn't work.

The basic tutorial 3 of the gstreamer sdk is a perfect example for what you're trying to do.