gstreamer -- appsrc

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可以通过appsrc将外部的数据添加到gstreamer 的 pipeline中，下面链接是appsrc 的一些说明（可能需要翻墙才能打开，其中还有appsink的一些说明和例子）

https://gstreamer.freedesktop.org/data/doc/gstreamer/head/manual/html/section-data-spoof.html

下面是其中的一例子

#include <gst/gst.h>static GMainLoop *loop;static voidcb_need_data (GstElement *appsrc,      guint       unused_size,      gpointer    user_data){  static gboolean white = FALSE;  static GstClockTime timestamp = 0;  GstBuffer *buffer;  guint size;  GstFlowReturn ret;  size = 385 * 288 * 2;  buffer = gst_buffer_new_allocate (NULL, size, NULL);  /* this makes the image black/white */  gst_buffer_memset (buffer, 0, white ? 0xff : 0x0, size);  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);  }}gintmain (gint   argc,      gchar *argv[]){  GstElement *pipeline, *appsrc, *conv, *videosink;  /* init GStreamer */  gst_init (&argc, &argv);  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 ("xvimagesink", "videosink");  /* setup */  g_object_set (G_OBJECT (appsrc), "caps",  gst_caps_new_simple ("video/x-raw",     "format", G_TYPE_STRING, "RGB16",     "width", G_TYPE_INT, 384,     "height", G_TYPE_INT, 288,     "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;  }

gstreamer也可以和opencv中mat链接起来，将下面的代码替换掉cb_need_data函数中相应的部分就可以了

GstMapInfo map;
gst_buffer_map(buffer,&map,GST_MAP_READ);
memcpy(map.data,ptr->input->data,size); //ptr->input 即一个mat指针
GST_BUFFER_PTS (buffer) = timestamp;
GST_BUFFER_DURATION (buffer) = gst_util_uint64_scale_int (1, GST_SECOND, 25);
timestamp += GST_BUFFER_DURATION (buffer) ;
g_signal_emit_by_name (appsrc, "push-buffer", buffer, &ret);
gst_buffer_unmap(buffer,&map);
gst_buffer_unref (buffer);

最后的gst_buffer_unmap()和gst_buffer_rnref()是释放内存空间，缺少的话会导致随着运行时间占用的内存会无限增长。

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