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_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
#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(¤t_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;
}
