gstreamer -- appsrc

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 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;

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);
}
}

gint
main (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。