how to deal with images stream?

andrea cinetto cinettoa at
Wed Jun 17 18:55:46 PDT 2015

Hi,I need to push open-cv images into a v4l2 device. After some googleing I found out that Gstreamer seems to be the best choice to do this. I completed the tutorials and I tried to build a pipeline made by appsrc, videoconvert and v4l2sink.  The problem is that I can not find enough documentation about v4l2sink so I cannot understand how to make it work! I am able to obtain the stream succesfully if I use a autovideosink element but when I switch to v4l2sink the system stops to work.
In the following code there is a simple example using just one image.Anybody know how to deal with this issue?Thanks,

#include <gst/gst.h>
#include <cv.h>
#include <highgui.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,depth,height,width,step,channels;
  GstFlowReturn ret;
  IplImage* img;
  guchar *data1;
  GstMapInfo map;
  g_print("image buffered");
  height    = img->height;  
  width     = img->width;
  step      = img->widthStep;
  channels  = img->nChannels;
  depth     = img->depth;
  data1      = (guchar *)img->imageData;
  size = height*width*channels;

  buffer = gst_buffer_new_allocate (NULL, size, NULL);
  gst_buffer_map (buffer, &map, GST_MAP_WRITE);
  memcpy( (guchar *), data1,  gst_buffer_get_size( buffer ) );

  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);

  if (ret != GST_FLOW_OK) {
    /* something wrong, stop pushing */
    g_main_loop_quit (loop);

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 ("v4l2sink", "videosink");

  /* setup */
  g_object_set (G_OBJECT (appsrc), "caps",
          gst_caps_new_simple ("video/x-raw",
                     "format", G_TYPE_STRING, "RGB",
                     "width", G_TYPE_INT, 640,
                     "height", G_TYPE_INT, 360,
                     "framerate", GST_TYPE_FRACTION, 1, 1,
                     NULL), NULL);
  gst_bin_add_many (GST_BIN (pipeline), appsrc, conv, videosink, NULL);
  gst_element_link_many (appsrc,conv, videosink, NULL);
  g_object_set (videosink, "device", "/dev/video0", NULL);
  //g_object_set (videosink, "flags", 0x00000002, NULL);
  //g_object_set (videosink, "io-mode", 4, 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;
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