GStreamer：一个包含三个元素的管道

先贴代码吧：

#include <gst/gst.h>

int main(int argc, char *argv[]) {
  GstElement *pipeline, *source, *sink;
  GstBus *bus;
  GstMessage *msg;
  GstStateChangeReturn ret;

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

  /* Create the elements */
  source = gst_element_factory_make("videotestsrc", "source");
  sink = gst_element_factory_make("autovideosink", "sink");

  /* Create the empty pipeline */
  pipeline = gst_pipeline_new("test-pipeline");

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

  /* Build the pipeline */
  gst_bin_add_many(GST_BIN (pipeline), source, sink, NULL);
  if (gst_element_link (source, sink) != TRUE) {
    g_printerr("Elements could not be linked.\n");
    gst_object_unref(pipeline);
    return -1;
  }

  /* Modify the source's properties */
  g_object_set(source, "pattern", 0, NULL);

  /* Start playing */
  ret = gst_element_set_state (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(pipeline);
    return -1;
  }

  /* Wait until error or EOS */
  bus = gst_element_get_bus(pipeline);
  msg = gst_bus_timed_pop_filtered(bus, GST_CLOCK_TIME_NONE, 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);
        break;
      case GST_MESSAGE_EOS:
        g_print("End-Of-Stream reached.\n");
        break;
      default:
        /* We should not reach here because we only asked for ERRORs and EOS */
        g_printerr("Unexpected message received.\n");
        break;
    }
    gst_message_unref(msg);
  }

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

代码精简如下：

	// 创建两个基本元素和一个管道
  	source = gst_element_factory_make("videotestsrc", "source");
  	sink = gst_element_factory_make("autovideosink", "sink");
	pipeline = gst_pipeline_new("test-pipeline");
	
	//把两个基本元素放到管道里面
	gst_bin_add_many(GST_BIN (pipeline), source, sink, NULL);
	
	//设置视频源类型
	g_object_set(source, "pattern", 0, NULL);

	//开始播放
	ret = gst_element_set_state (pipeline, GST_STATE_PLAYING);

	//在窗口显示视频
	bus = gst_element_get_bus(pipeline);
	msg = gst_bus_timed_pop_filtered(bus, GST_CLOCK_TIME_NONE, GST_MESSAGE_ERROR | GST_MESSAGE_EOS);

source、sink、pipeline 之间的关系如下：