I am building an app that can stream my webcam to a shared memory using shmsink plugin, and elsewhere get it using shmsrc and registering it to a file.
The following works perfectly :

Creating the shm source: gst-launch-1.0 v4l2src device=“/dev/video0” ! image/jpeg,width=1280,height=720,framerate=30/1 ! queue ! shmsink socket-path=/dev/shm/shm_test1

Getting the shared memory and registering it to a file:
gst-launch-1.0 -e shmsrc socket-path=/dev/shm/shm_test1 ! “image/jpeg,width=1280,height=720,framerate=30/1” ! jpegdec ! videoconvert ! “video/x-raw,format=I420” ! avimux ! filesink location=./test.avi

Now I wanted to turn that into actual code. I managed to create a class to stream the shared memory. But I am not able to do the second part, using it and recording it. This is the code that keeps failing :

bool Recorder::createPipeline() {
  gboolean status;
    shmSrc = gst_element_factory_make("shmsrc", "shm_source");
    jpegDec = gst_element_factory_make("jpegdec", "jpeg_decoder");
    videoConvert = gst_element_factory_make("videoconvert", "video_converter");
    aviMux = gst_element_factory_make("avimux", "avi_muxer");
    filesink = gst_element_factory_make("filesink", "file_sink");

    if (!shmSrc || !jpegDec || !videoConvert || !aviMux || !filesink) {
        g_printerr("Failed to create elementsn");
        return false;
    }

    g_object_set(shmSrc, "socket-path", shm_name.c_str(), NULL);
    g_object_set(filesink, "location", output_file.c_str(), NULL);

    GstCaps *caps = gst_caps_from_string("image/jpeg,width=1280,height=720,framerate=30/1");

    pipeline = gst_pipeline_new("recorder_pipeline");

    gst_bin_add_many(GST_BIN(pipeline), shmSrc, jpegDec, videoConvert, aviMux, filesink, NULL);

    if (!gst_element_link_many(shmSrc, jpegDec, videoConvert, aviMux, filesink, NULL)) {
        g_printerr("Failed to link elementsn");
        gst_object_unref(pipeline);
        return false;
    }

    status = link_elements_with_filter(shmSrc, jpegDec);
    if (!status) {
        g_printerr("Existing from createPipelinen");
        gst_caps_unref(caps);
        gst_object_unref(pipeline);
        return false;
    }
    gst_caps_unref(caps);
    return true;
}

gboolean Recorder::link_elements_with_filter(GstElement* element1, GstElement* element2) {
  gboolean link_ok;
  GstCaps* caps;
  caps = gst_caps_from_string("image/jpeg,width=1280,height=720,framerate=30/1");
  link_ok = gst_element_link_filtered(element1, element2, caps);
  gst_caps_unref(caps);
  if (!link_ok) {
    g_printerr("Failed to link elementsn");
  }
  return link_ok;
}

Specifically, it is the link elements with filter that keeps failing and I dont understand why. Any help would be appreciated !

EDIT1: Fixed code formatting.

EDIT2: I managed to make it work using gst_parse_launch() but I don’t understand why I can’t link a capsfilter…

bool Recorder::createPipeline() {
  std::string pipeline_description = "shmsrc socket-path=" + shm_name + 
                                     " ! image/jpeg,width=1280,height=720,framerate=30/1 ! jpegdec ! videoconvert ! avimux ! filesink location=" + output_file;

  GError *error = nullptr;
  pipeline = gst_parse_launch(pipeline_description.c_str(), &error);
  if (!pipeline) {
    g_printerr("Failed to create pipeline: %sn", error->message);
    g_error_free(error);
    return false;
  }

  bus = gst_element_get_bus(pipeline);

  return true;
}

void Recorder::start() {
  running = true;
  gst_element_set_state(pipeline, GST_STATE_PLAYING);
  bus_watch_thread = std::thread(&Recorder::bus_watch_thread_func, this);
} 

Why does the capsfilter linking fails using dynamic pipelining but not when using gst_parse_launch() static pipeline ?