Failed to dynamically switching an element with a nvoverlaysink plugin in gstreamer.


This example is dynamically changing element.

I tested a below example.

#include <gst/gst.h>

static gchar *opt_effects = NULL;

#define DEFAULT_EFFECTS "identity,exclusion,navigationtest," \

static GstPad *blockpad;
static GstElement *conv_before;
static GstElement *conv_after;
static GstElement *cur_effect;
static GstElement *pipeline;

static GQueue effects = G_QUEUE_INIT;

static GstPadProbeReturn
event_probe_cb (GstPad * pad, GstPadProbeInfo * info, gpointer user_data)
  GMainLoop *loop = user_data;
  GstElement *next;

    return GST_PAD_PROBE_PASS;

  gst_pad_remove_probe (pad, GST_PAD_PROBE_INFO_ID (info));

  /* push current effect back into the queue */
  g_queue_push_tail (&effects, gst_object_ref (cur_effect));
  /* take next effect from the queue */
  next = g_queue_pop_head (&effects);
  if (next == NULL) {
    GST_DEBUG_OBJECT (pad, "no more effects");
    g_main_loop_quit (loop);
    return GST_PAD_PROBE_DROP;

  g_print ("Switching from '%s' to '%s'..\n", GST_OBJECT_NAME (cur_effect),
      GST_OBJECT_NAME (next));

  gst_element_set_state (cur_effect, GST_STATE_NULL);

  /* remove unlinks automatically */
  GST_DEBUG_OBJECT (pipeline, "removing %" GST_PTR_FORMAT, cur_effect);
  gst_bin_remove (GST_BIN (pipeline), cur_effect);

  GST_DEBUG_OBJECT (pipeline, "adding   %" GST_PTR_FORMAT, next);
  gst_bin_add (GST_BIN (pipeline), next);

  GST_DEBUG_OBJECT (pipeline, "linking..");
  gst_element_link_many (conv_before, next, conv_after, NULL);

  gst_element_set_state (next, GST_STATE_PLAYING);

  cur_effect = next;
  GST_DEBUG_OBJECT (pipeline, "done");


static GstPadProbeReturn
pad_probe_cb (GstPad * pad, GstPadProbeInfo * info, gpointer user_data)
  GstPad *srcpad, *sinkpad;

  GST_DEBUG_OBJECT (pad, "pad is blocked now");

  /* remove the probe first */
  gst_pad_remove_probe (pad, GST_PAD_PROBE_INFO_ID (info));

  /* install new probe for EOS */
  srcpad = gst_element_get_static_pad (cur_effect, "src");
  gst_pad_add_probe (srcpad, GST_PAD_PROBE_TYPE_BLOCK |
      GST_PAD_PROBE_TYPE_EVENT_DOWNSTREAM, event_probe_cb, user_data, NULL);
  gst_object_unref (srcpad);

  /* push EOS into the element, the probe will be fired when the
   * EOS leaves the effect and it has thus drained all of its data */
  sinkpad = gst_element_get_static_pad (cur_effect, "sink");
  gst_pad_send_event (sinkpad, gst_event_new_eos ());
  gst_object_unref (sinkpad);

  return GST_PAD_PROBE_OK;

static gboolean
timeout_cb (gpointer user_data)
  gst_pad_add_probe (blockpad, GST_PAD_PROBE_TYPE_BLOCK_DOWNSTREAM,
      pad_probe_cb, user_data, NULL);

  return TRUE;

static gboolean
bus_cb (GstBus * bus, GstMessage * msg, gpointer user_data)
  GMainLoop *loop = user_data;

  switch (GST_MESSAGE_TYPE (msg)) {
      GError *err = NULL;
      gchar *dbg;

      gst_message_parse_error (msg, &err, &dbg);
      gst_object_default_error (msg->src, err, dbg);
      g_clear_error (&err);
      g_free (dbg);
      g_main_loop_quit (loop);
  return TRUE;

main (int argc, char **argv)
  GOptionEntry options[] = {
    {"effects", 'e', 0, G_OPTION_ARG_STRING, &opt_effects,
        "Effects to use (comma-separated list of element names)", NULL},
  GOptionContext *ctx;
  GError *err = NULL;
  GMainLoop *loop;
  GstElement *src, *q1, *q2, *effect, *filter1, *filter2, *sink;
  gchar **effect_names, **e;

  ctx = g_option_context_new ("");
  g_option_context_add_main_entries (ctx, options, NULL);
  g_option_context_add_group (ctx, gst_init_get_option_group ());
  if (!g_option_context_parse (ctx, &argc, &argv, &err)) {
    g_print ("Error initializing: %s\n", err->message);
    g_clear_error (err);
    g_option_context_free (ctx);
    return 1;
  g_option_context_free (ctx);

  if (opt_effects != NULL)
    effect_names = g_strsplit (opt_effects, ",", -1);
    effect_names = g_strsplit (DEFAULT_EFFECTS, ",", -1);

  for (e = effect_names; e != NULL && *e != NULL; ++e) {
    GstElement *el;

    el = gst_element_factory_make (*e, NULL);
    if (el) {
      g_print ("Adding effect '%s'\n", *e);
      g_queue_push_tail (&effects, el);

  pipeline = gst_pipeline_new ("pipeline");

  src = gst_element_factory_make ("videotestsrc", NULL);
  g_object_set (src, "is-live", TRUE, NULL);

  filter1 = gst_element_factory_make ("capsfilter", NULL);
  gst_util_set_object_arg (G_OBJECT (filter1), "caps",
      "video/x-raw, width=320, height=240, "
      "format={ I420, YV12, YUY2, UYVY, AYUV, Y41B, Y42B, "
      "YVYU, Y444, v210, v216, NV12, NV21, UYVP, A420, YUV9, YVU9, IYU1 }");

  q1 = gst_element_factory_make ("queue", NULL);

  blockpad = gst_element_get_static_pad (q1, "src");

  conv_before = gst_element_factory_make ("videoconvert", NULL);

  effect = g_queue_pop_head (&effects);
  cur_effect = effect;

  conv_after = gst_element_factory_make ("videoconvert", NULL);

  q2 = gst_element_factory_make ("queue", NULL);

  filter2 = gst_element_factory_make ("capsfilter", NULL);
  gst_util_set_object_arg (G_OBJECT (filter2), "caps",
      "video/x-raw, width=320, height=240, "
      "format={ RGBx, BGRx, xRGB, xBGR, RGBA, BGRA, ARGB, ABGR, RGB, BGR }");

  sink = gst_element_factory_make ("ximagesink", NULL);

  gst_bin_add_many (GST_BIN (pipeline), src, filter1, q1, conv_before, effect,
      conv_after, q2, sink, NULL);

  gst_element_link_many (src, filter1, q1, conv_before, effect, conv_after,
      q2, sink, NULL);

  gst_element_set_state (pipeline, GST_STATE_PLAYING);

  loop = g_main_loop_new (NULL, FALSE);

  gst_bus_add_watch (GST_ELEMENT_BUS (pipeline), bus_cb, loop);

  g_timeout_add_seconds (1, timeout_cb, loop);

  g_main_loop_run (loop);

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

  return 0;

It is successful.

And I changed a nvoverlaysink element from a ximagesink;(LINE. 186).

sink = gst_element_factory_make ("ximagesink", NULL);

It occurred a segmentation fault or blocked below.

Adding effect 'identity'
Adding effect 'exclusion'
Adding effect 'navigationtest'
Adding effect 'agingtv'
Adding effect 'videoflip'
Adding effect 'vertigotv'
Adding effect 'gaussianblur'
Adding effect 'shagadelictv'
Adding effect 'edgetv'
Switching from 'identity0' to 'exclusion0'..
Segmentation fault (core dumped)

I want to know what caused the problem and how to fix it.

Jetson TX2, Jetpack 3.2.1, Gstreamer version 1.8.3

Hi iamlow,
It is possible to reproduce your issue in single pipeline?

Yes, it is possible.

The example above consists of a single pipeline.

Hi iamlow,
Please share the single pipelie to reproduce the issue. We can study your code but it will take some time. It is better you can directly give us the pipeline.

I don’t understand about your request.
What does mean “single pipeline to reproduce the problem” ? Diagram? Scripts using gst-launch-1.0?

My example code is in a tutorial here.

I just tested it by changing a nvoverlaysink from a ximagesink in the example above.

Yes, a gst-launch-1.0 pipeline to reproduce the issue.

This issue is not possible using a gst-launch-1.0.
Because the structure of the pipeline must be dynamically changed during execution.

Hi iamlow,
Can you try to have nvvidconv along with nvoverlaysink? Like “nvvidconv ! ‘video/x-raw(memory:NVMM),format=I420’ ! nvoverlaysink”


I added a nvvidconv plugin and it was successful.
The issue is solved.