GStreamer Development

Abstract

GStreamer Development

Category

Learning note

Authors

Walter Fan

Status

WIP

Updated

2024-08-21

应用开发

以一个测试视频回放流程为例

  1. 初始化 GStreamer:

  2. 创建 pipeline

  3. 创建所需的 element

  4. 将 element 放到 pipeline 中，并连接它们

  5. 设置好相关属性和回调

  6. 设置 pipeline 状态，启动主循环

示例

#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;
}

插件开发

以一个 filter 插件为例

git clone https://gitlab.freedesktop.org/gstreamer/gst-template.git
cd gst-template/gst-plugin/src
../tools/make_element MyFilter

由模板自动生成的代码如下

#ifndef __GST_MYFILTER_H__
#define __GST_MYFILTER_H__

#include <gst/gst.h>

G_BEGIN_DECLS

/* #defines don't like whitespacey bits */
#define GST_TYPE_MYFILTER \
(gst_my_filter_get_type())
#define GST_MYFILTER(obj) \
(G_TYPE_CHECK_INSTANCE_CAST((obj),GST_TYPE_MYFILTER,GstMyFilter))
#define GST_MYFILTER_CLASS(klass) \
(G_TYPE_CHECK_CLASS_CAST((klass),GST_TYPE_MYFILTER,GstMyFilterClass))
#define GST_IS_MYFILTER(obj) \
(G_TYPE_CHECK_INSTANCE_TYPE((obj),GST_TYPE_MYFILTER))
#define GST_IS_MYFILTER_CLASS(klass) \
(G_TYPE_CHECK_CLASS_TYPE((klass),GST_TYPE_MYFILTER))

typedef struct _GstMyFilter      GstMyFilter;
typedef struct _GstMyFilterClass GstMyFilterClass;

struct _GstMyFilter
{
   GstElement element;

   GstPad *sinkpad, *srcpad;

   gboolean silent;
};

struct _GstMyFilterClass
{
   GstElementClass parent_class;
};

GType gst_my_filter_get_type (void);

G_END_DECLS

#endif /* __GST_MYFILTER_H__ */

  1. 获取插件模板

  2. 设置新的 element 的属性，如名称，作者，版本号

  3. 注册此插件 _class_init

  4. 定义新的 element 所需的 pad 及其属性，类型及其所支持类型的列表

  5. 实现 plugin_init 函数，在插件加载后立即调用

  6. 实现

Reference