gstreamer使用cairo实现视频OSD叠加

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

cpp 复制代码

#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_overlay (GstElement * overlay, cairo_t * cr, guint64 timestamp,
    guint64 duration, gpointer user_data)
{
  CairoOverlayState *s = (CairoOverlayState *) user_data;
  double scale;
  int width, height;

  if (!s->valid)
    return;

  width = GST_VIDEO_INFO_WIDTH (&s->vinfo);
  height = GST_VIDEO_INFO_HEIGHT (&s->vinfo);

  scale = 2 * (((timestamp / (int) 1e7) % 70) + 30) / 100.0;
  cairo_translate (cr, width / 2, (height / 2) - 30);

  /* FIXME: this assumes a pixel-aspect-ratio of 1/1 */
  cairo_scale (cr, scale, scale);

  cairo_move_to (cr, 0, 0);
  cairo_curve_to (cr, 0, -30, -50, -30, -50, 0);
  cairo_curve_to (cr, -50, 30, 0, 35, 0, 60);
  cairo_curve_to (cr, 0, 35, 50, 30, 50, 0);
  cairo_curve_to (cr, 50, -30, 0, -30, 0, 0);
  cairo_set_source_rgba (cr, 0.9, 0.0, 0.1, 0.7);
  cairo_fill (cr);
}

static GstElement *
setup_gst_pipeline (CairoOverlayState * overlay_state)
{
  GstElement *pipeline;
  GstElement *cairo_overlay;
  GstElement *source, *adaptor1, *adaptor2, *sink;

  pipeline = gst_pipeline_new ("cairo-overlay-example");

  /* Adaptors needed because cairooverlay only supports ARGB data */
  source = gst_element_factory_make ("videotestsrc", "source");
  adaptor1 = gst_element_factory_make ("videoconvert", "adaptor1");
  cairo_overlay = gst_element_factory_make ("cairooverlay", "overlay");
  adaptor2 = gst_element_factory_make ("videoconvert", "adaptor2");
  sink = gst_element_factory_make ("ximagesink", "sink");
  if (sink == NULL)
    sink = gst_element_factory_make ("autovideosink", "sink");

  /* If failing, the element could not be created */
  g_assert (cairo_overlay);

  /* Hook up the necessary signals for cairooverlay */
  g_signal_connect (cairo_overlay, "draw",
      G_CALLBACK (draw_overlay), overlay_state);
  g_signal_connect (cairo_overlay, "caps-changed",
      G_CALLBACK (prepare_overlay), overlay_state);

  gst_bin_add_many (GST_BIN (pipeline), source, adaptor1,
      cairo_overlay, adaptor2, sink, NULL);

  if (!gst_element_link_many (source, adaptor1,
          cairo_overlay, adaptor2, sink, NULL)) {
    g_warning ("Failed to link elements!");
  }

  return pipeline;
}

int
main (int argc, char **argv)
{
  GMainLoop *loop;
  GstElement *pipeline;
  GstBus *bus;
  CairoOverlayState *overlay_state;

  gst_init (&argc, &argv);
  loop = g_main_loop_new (NULL, FALSE);

  /* allocate on heap for pedagogical reasons, makes code easier to transfer */
  overlay_state = g_new0 (CairoOverlayState, 1);

  pipeline = setup_gst_pipeline (overlay_state);

  bus = gst_pipeline_get_bus (GST_PIPELINE (pipeline));
  gst_bus_add_signal_watch (bus);
  g_signal_connect (G_OBJECT (bus), "message", G_CALLBACK (on_message), loop);
  gst_object_unref (GST_OBJECT (bus));

  gst_element_set_state (pipeline, GST_STATE_PLAYING);
  g_main_loop_run (loop);

  gst_element_set_state (pipeline, GST_STATE_NULL);
  gst_object_unref (pipeline);

  g_free (overlay_state);
  return 0;
}

显示实时时间

main.cpp

cpp 复制代码

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

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

#include <glib.h>
#include <time.h>
#include <string>
using std::string;

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_overlay (GstElement * overlay, cairo_t * cr, guint64 timestamp,
    guint64 duration, gpointer user_data)
{
  CairoOverlayState *s = (CairoOverlayState *) user_data;
  string text = "Current Time: ";
  time_t current_time = time(NULL); // 获取当前时间
  struct tm *tm_info = localtime(&current_time); // 将当前时间转换为本地时间
  char time_str[21]; // 足够存储 "YYYY-MM-DD HH:MM:SS" 格式的时间字符串
  double scale;
  int width, height;

  if (!s->valid)
    return;

  // 格式化时间为 "YYYY-MM-DD HH:MM:SS" 格式
  strftime(time_str, sizeof(time_str), "%Y-%m-%d %H:%M:%S", tm_info);
  text.append(time_str);

  // 移动位置:到中心
  width = GST_VIDEO_INFO_WIDTH (&s->vinfo);
  height = GST_VIDEO_INFO_HEIGHT (&s->vinfo);
  cairo_translate (cr, width / 2, height / 2);

  // 比例调整
  //cairo_scale (cr, 2.0, 2.0);

  // 设置文本颜色和透明度
  cairo_set_source_rgba (cr, 0.0, 0.0, 0.0, 1.0); // 黑色文本
  cairo_select_font_face (cr, "Sans", CAIRO_FONT_SLANT_NORMAL, CAIRO_FONT_WEIGHT_BOLD);
  cairo_set_font_size (cr, 24);
  // 绘制文本

  cairo_show_text (cr, text.c_str());

}

static GstElement *
setup_gst_pipeline (CairoOverlayState * overlay_state)
{
  GstElement *pipeline;
  GstCaps *caps;
  GstElement *cairo_overlay;
  GstElement *source, *capsfilter, *adaptor1, *adaptor2, *sink;

  pipeline = gst_pipeline_new ("cairo-overlay-example");

  // 创建元素
  /* Adaptors needed because cairooverlay only supports ARGB data */
  source = gst_element_factory_make ("videotestsrc", "source");
  capsfilter = gst_element_factory_make ("capsfilter", "capsfilter");
  adaptor1 = gst_element_factory_make ("videoconvert", "adaptor1");
  cairo_overlay = gst_element_factory_make ("cairooverlay", "overlay");
  adaptor2 = gst_element_factory_make ("videoconvert", "adaptor2");
  sink = gst_element_factory_make ("glimagesink", "sink");
  if (sink == NULL)
    sink = gst_element_factory_make ("autovideosink", "sink");

  /* If failing, the element could not be created */
  g_assert (cairo_overlay);

  // 设置输出参数
  caps = gst_caps_new_simple ("video/x-raw",
                              "width", G_TYPE_INT, 960,
                              "height", G_TYPE_INT, 480,
                              "framerate", GST_TYPE_FRACTION, 60, 1,
                              NULL);
  g_object_set (G_OBJECT (capsfilter), "caps", caps, NULL);
  gst_caps_unref (caps);

  // 联通信号和回调函数
  /* Hook up the necessary signals for cairooverlay */
  g_signal_connect (cairo_overlay, "draw",
      G_CALLBACK (draw_overlay), overlay_state);
  g_signal_connect (cairo_overlay, "caps-changed",
      G_CALLBACK (prepare_overlay), overlay_state);

  gst_bin_add_many (GST_BIN (pipeline), source, capsfilter,adaptor1,
      cairo_overlay, adaptor2, sink, NULL);

  if (!gst_element_link_many (source, capsfilter,adaptor1,
          cairo_overlay, adaptor2, sink, NULL)) {
    g_warning ("Failed to link elements!");
  }

  return pipeline;
}

int main (int argc, char **argv)
{
  GMainLoop *loop;
  GstElement *pipeline;
  GstBus *bus;
  CairoOverlayState *overlay_state;

  gst_init (&argc, &argv);
  loop = g_main_loop_new (NULL, FALSE);

  /* allocate on heap for pedagogical reasons, makes code easier to transfer */
  overlay_state = g_new0 (CairoOverlayState, 1);

  pipeline = setup_gst_pipeline (overlay_state);

  bus = gst_pipeline_get_bus (GST_PIPELINE (pipeline));
  gst_bus_add_signal_watch (bus);
  g_signal_connect (G_OBJECT (bus), "message", G_CALLBACK (on_message), loop);
  gst_object_unref (GST_OBJECT (bus));

  gst_element_set_state (pipeline, GST_STATE_PLAYING);
  g_main_loop_run (loop);

  gst_element_set_state (pipeline, GST_STATE_NULL);
  gst_object_unref (pipeline);

  g_free (overlay_state);
  return 0;
}