Gstreamer学习3----灌数据给管线之appsrc

参考资料

Basic tutorial 8: Short-cutting the pipeline

gstreamer向appsrc发送帧画面的代码_gst appsrc可变帧率-CSDN博客

在官网教程Basic tutorial 8: Short-cutting the pipeline

里面，讲了一个例子，push音频数据给管线，视频的例子更加直观一些，

主要步骤：

注册一个回调，

g_signal_connect(appsrc, "need-data", G_CALLBACK(cb_need_data), NULL);

回调方法中，设置数据，再push进处理流程中

g_signal_emit_by_name(appsrc, "push-buffer", buffer, &ret);

这个g_signal_emit_by_name(appsrc, "push-buffer", buffer, &ret);是个同步阻塞方法，因为ret作为入参，记录执行的情况。

#include <gst/gst.h>
#define VIDEO_WIDTH   384
#define VIDEO_HEIGHT  288
#define VIDEO_FORMAT  "RGB16"
#define PIXEL_SIZE    2

static void cb_need_data(GstElement* appsrc, guint unused_size, gpointer user_data)
{
  static gboolean white = FALSE;
  static GstClockTime timestamp = 0;
  GstBuffer* buffer;
  guint size;
  GstFlowReturn ret;
  g_print("cb_need_data called\n");
  static unsigned char color = 0;

  size = VIDEO_WIDTH * VIDEO_HEIGHT * PIXEL_SIZE;
  buffer = gst_buffer_new_allocate(NULL, size, NULL);
  /* this makes the image black/white */
 // gst_buffer_memset(buffer, 0, white ? 0xFF : 0x00, size);
  gst_buffer_memset(buffer, 0, color, size);
  color += 10;

 // white = !white;
  GST_BUFFER_PTS(buffer) = timestamp;
  GST_BUFFER_DURATION(buffer) = gst_util_uint64_scale_int(1, GST_SECOND, 2);
  timestamp += GST_BUFFER_DURATION(buffer);
  g_signal_emit_by_name(appsrc, "push-buffer", buffer, &ret);
  gst_buffer_unref(buffer);
  if (ret != GST_FLOW_OK)
  {
    /* something wrong, stop pushing */
  //  g_main_loop_quit(loop);
  }
}

gint main(gint argc, gchar* argv[])
{
  GstElement* pipeline, * appsrc, * conv, * videosink;
  GMainLoop* loop;
  /* init GStreamer */
  gst_init(NULL, NULL);
  loop = g_main_loop_new(NULL, FALSE);
  /* setup pipeline */
  pipeline = gst_pipeline_new("pipeline");
  appsrc = gst_element_factory_make("appsrc", "source");
  conv = gst_element_factory_make("videoconvert", "conv");
  videosink = gst_element_factory_make("autovideosink", "videosink");
  /* setup */
  g_object_set(G_OBJECT(appsrc), "caps",
    gst_caps_new_simple("video/x-raw",
      "format", G_TYPE_STRING, VIDEO_FORMAT,
      "width", G_TYPE_INT, VIDEO_WIDTH,
      "height", G_TYPE_INT, VIDEO_HEIGHT,
      "framerate", GST_TYPE_FRACTION, 0, 1,
      NULL), NULL);
  gst_bin_add_many(GST_BIN(pipeline), appsrc, conv, videosink, NULL);
  gst_element_link_many(appsrc, conv, videosink, NULL);
  /* setup appsrc */
  g_object_set(G_OBJECT(appsrc),
    "stream-type", 0,
    "format", GST_FORMAT_TIME, NULL);
  g_signal_connect(appsrc, "need-data", G_CALLBACK(cb_need_data), NULL);
  /* play */
  gst_element_set_state(pipeline, GST_STATE_PLAYING);
  g_main_loop_run(loop);
  /* clean up */
  gst_element_set_state(pipeline, GST_STATE_NULL);
  gst_object_unref(GST_OBJECT(pipeline));
  g_main_loop_unref(loop);
  return 0;
}

可以看到颜色变化的画面