前言

gstreamer中视频叠加OSD有很多种方式，比如textoverlay添加文字，gdkpixbufoverlay添加图片，clockoverlay或timeoverlay插件显示时间，pango插件进行复杂文本渲染，使用cairo插件绘制图形或者文字。

今天使用最后一种：cairo

项目源码：

如果是QT，pro文件需要导入：

pro:

PKGCONFIG += cairo

INCLUDEPATH += /usr/include/cairo/

显示动态心♥

main.cpp

#include <gst/gst.h>
#include <gst/video/video.h>

#include <cairo/cairo.h>
#include <cairo/cairo-gobject.h>

#include <glib.h>


static gboolean
on_message (GstBus * bus, GstMessage * message, gpointer user_data)
{
  GMainLoop *loop = (GMainLoop *) user_data;

  switch (GST_MESSAGE_TYPE (message)) {
    case GST_MESSAGE_ERROR:{
      GError *err = NULL;
      gchar *debug;

      gst_message_parse_error (message, &err, &debug);
      g_critical ("Got ERROR: %s (%s)", err->message, GST_STR_NULL (debug));
      g_main_loop_quit (loop);
      break;
    }
    case GST_MESSAGE_WARNING:{
      GError *err = NULL;
      gchar *debug;

      gst_message_parse_warning (message, &err, &debug);
      g_warning ("Got WARNING: %s (%s)", err->message, GST_STR_NULL (debug));
      g_main_loop_quit (loop);
      break;
    }
    case GST_MESSAGE_EOS:
      g_main_loop_quit (loop);
      break;
    default:
      break;
  }

  return TRUE;
}

/* Datastructure to share the state we are interested in between
 * prepare and render function. */
typedef struct
{
  gboolean valid;
  GstVideoInfo vinfo;
} CairoOverlayState;

/* Store the information from the caps that we are interested in. */
static void
prepare_overlay (GstElement * overlay, GstCaps * caps, gpointer user_data)
{
  CairoOverlayState *state = (CairoOverlayState *) user_data;

  state->valid = gst_video_info_from_caps (&state->vinfo, caps);
}

/* Draw the overlay.
 * This function draws a cute "beating" heart. */
static void
draw_