tutorial_3.cpp

#include <gst/gst.h>

struct CustomData
{
  GstElement *pipeline;
  GstElement *source;
  GstElement *convert;
  GstElement *resample;
  GstElement *sink;

  GstElement *videoconvert;
  GstElement *videosink;
};

/* handler for the pad-added singnal */
static void pad_added_handler(GstElement *src, GstPad *pad, CustomData *data);

int main(int argc, char *argv[])
{
  CustomData data;
  GstBus *bus;
  GstMessage *msg;
  GstStateChangeReturn ret;
  gboolean terminate = FALSE;
  GMainLoop *main_loop;

  /* Initialize GStreamer */
  gst_init(&argc, &argv);

  /* Create the elements */
  data.source = gst_element_factory_make("uridecodebin", "source");

  /* Elements responsible for audio processing*/
  data.convert = gst_element_factory_make("audioconvert", "convert");
  data.resample = gst_element_factory_make("audioresample", "resample");
  data.sink = gst_element_factory_make("autoaudiosink", "sink");

  /* Elements responsible for video processing*/
  data.videoconvert = gst_element_factory_make("videoconvert", "videoconvert");
  data.videosink = gst_element_factory_make("autovideosink", "videosink");

  /* Create the empty pipeline */
  data.pipeline = gst_pipeline_new("tesst-pipeline");

  if (!data.pipeline || !data.source || !data.convert || !data.resample || !data.sink)
  {
    g_printerr("Not all elements could be created.\n");
    return -1;
  }

  /* Build the pipeline */
  /* Build the pipeline. Note that we are NOT linking the source at this
   * point. We will do it later. */
  gst_bin_add_many(GST_BIN(data.pipeline), data.source, data.convert, data.videoconvert, data.videosink, data.resample, data.sink, NULL);

  // Connect elements responsible for audio processing.
  if (!gst_element_link_many(data.convert, data.resample, data.sink, NULL))
  {
    g_printerr("Elements could not be linked.\n");
    gst_object_unref(data.pipeline);
    return -1;
  }

  // Connect elements responsible for video processing.
  if (!gst_element_link_many(data.videoconvert, data.videosink, NULL))
  {
    g_printerr("Elements data.videoconvert, data.videosin could not be linked.\n");
    gst_object_unref(data.pipeline);
    return -1;
  }

  /* Set the URI to play */
  g_object_set(data.source, "uri", "https://www.freedesktop.org/software/gstreamer-sdk/data/media/sintel_trailer-480p.webm", NULL);

  /* Connect to the pad-added signal */
  g_signal_connect(data.source, "pad-added", G_CALLBACK(pad_added_handler), &data);

  /* Start playing */
  ret = gst_element_set_state(data.pipeline, GST_STATE_PLAYING);
  if (ret == GST_STATE_CHANGE_FAILURE)
  {
    g_printerr("Unable to set the pipeline to the playing state.\n");
    gst_object_unref(data.pipeline);
    return -1;
  }
  main_loop = g_main_loop_new(NULL, FALSE);
  g_main_loop_run(main_loop);

  /* Listen to the bus */
  bus = gst_element_get_bus(data.pipeline);
  do
  {
    msg = gst_bus_timed_pop_filtered(bus, GST_CLOCK_TIME_NONE,
                                     (GstMessageType)(GST_MESSAGE_STATE_CHANGED | GST_MESSAGE_ERROR | GST_MESSAGE_EOS));

    /* Parse message */
    if (msg != NULL)
    {
      GError *err;
      gchar *debug_info;

      switch (GST_MESSAGE_TYPE(msg))
      {
      case GST_MESSAGE_ERROR:
        gst_message_parse_error(msg, &err, &debug_info);
        g_printerr("Error received from element %s: %s\n", GST_OBJECT_NAME(msg->src), err->message);
        g_printerr("Debugging information: %s\n", debug_info ? debug_info : "none");
        g_clear_error(&err);
        g_free(debug_info);
        terminate = TRUE;
        break;
      case GST_MESSAGE_EOS:
        g_print("End-Of-Stream reached.\n");
        terminate = TRUE;
        break;
      case GST_MESSAGE_STATE_CHANGED:
        /* We are only interested in state-changed messages from the pipeline */
        if (GST_MESSAGE_SRC(msg) == GST_OBJECT(data.pipeline))
        {
          GstState old_state, new_state, pending_state;
          gst_message_parse_state_changed(msg, &old_state, &new_state, &pending_state);
          g_print("Pipeline state changed from %s to %s:\n",
                  gst_element_state_get_name(old_state), gst_element_state_get_name(new_state));
        }
        break;
      default:
        /* We should not reach here */
        g_printerr("Unexpected message received.\n");
        break;
      }
      gst_message_unref(msg);
    }
  } while (!terminate);

  /* Free resources */
  gst_object_unref(bus);
  gst_element_set_state(data.pipeline, GST_STATE_NULL);
  gst_object_unref(data.pipeline);
  return 0;
}

static void pad_added_handler(GstElement *src, GstPad *new_pad, CustomData *data)
{
  GstPad *sink_pad = gst_element_get_static_pad(data->convert, "sink");
  GstPad *sink_video_pad = gst_element_get_static_pad(data->videoconvert, "sink");
  GstPadLinkReturn ret;
  GstCaps *new_pad_caps = NULL;
  GstStructure *new_pad_struct = NULL;
  const gchar *new_pad_type = NULL;

  g_print("Received new pad '%s' from '%s':\n", GST_PAD_NAME(new_pad), GST_ELEMENT_NAME(src));

  /* Check the new pad's type */
  new_pad_caps = gst_pad_get_current_caps(new_pad);
  new_pad_struct = gst_caps_get_structure(new_pad_caps, 0);
  new_pad_type = gst_structure_get_name(new_pad_struct);
  if (g_str_has_prefix(new_pad_type, "audio/x-raw"))
  {
    /* Attempt the link */
    ret = gst_pad_link(new_pad, sink_pad);
    g_print("Linked audio pad.\n");
    if (GST_PAD_LINK_FAILED(ret))
    {
      g_print("Type is '%s' but link failed.\n", new_pad_type);
    }
    else
    {
      g_print("Link succeeded (type '%s').\n", new_pad_type);
    }
  }
  else if (g_str_has_prefix(new_pad_type, "video/x-raw"))
  {
    /* Attempt the link */
    ret = gst_pad_link(new_pad, sink_video_pad);
    g_print("Linked video pad.\n");
    if (GST_PAD_LINK_FAILED(ret))
    {
      g_print("Type is '%s' but link failed.\n", new_pad_type);
    }
    else
    {
      g_print("Link succeeded (type '%s').\n", new_pad_type);
    }
  }

exit:
  /* Unreference the new pad's caps, if we got them */
  if (new_pad_caps != NULL)
    gst_caps_unref(new_pad_caps);

  /* Unreference the sink pad */
  gst_object_unref(sink_pad);
}