Save metadata along with images in dsexample

I am currenty using the dsexample plugin to save images using the below code. I need help in accessing the meta data while saving images. Right now dump is just a static counter which is used to name images. I want to save images with the corresponding frame_num as the name and also a seperate text file with the meta data. I am having problems accessing the meta data and passing it to the corresponding function.

static GstFlowReturn
get_converted_mat (GstDsExample * dsexample, NvBufSurface *input_buf, gint idx,
    NvOSD_RectParams * crop_rect_params, gdouble & ratio, gint input_width,
    gint input_height)
  NvBufSurfTransform_Error err;
  NvBufSurfTransformConfigParams transform_config_params;
  NvBufSurfTransformParams transform_params;
  NvBufSurfTransformRect src_rect;
  NvBufSurfTransformRect dst_rect;
  NvBufSurface ip_surf;
  cv::Mat in_mat, out_mat;
  ip_surf = *input_buf;

  ip_surf.numFilled = ip_surf.batchSize = 1;
  ip_surf.surfaceList = &(input_buf->surfaceList[idx]);

  gint src_left = GST_ROUND_UP_2(crop_rect_params->left);
  gint src_top = GST_ROUND_UP_2(crop_rect_params->top);
  gint src_width = GST_ROUND_DOWN_2(crop_rect_params->width);
  gint src_height = GST_ROUND_DOWN_2(crop_rect_params->height);
  //g_print("ltwh = %d %d %d %d \n", src_left, src_top, src_width, src_height);

  guint dest_width, dest_height;
  dest_width = src_width;
  dest_height = src_height;

  NvBufSurface *nvbuf;
  NvBufSurfaceCreateParams create_params;
  create_params.gpuId  = dsexample->gpu_id;
  create_params.width  = dest_width;
  create_params.height = dest_height;
  create_params.size = 0;
  create_params.colorFormat = NVBUF_COLOR_FORMAT_RGBA;
  create_params.layout = NVBUF_LAYOUT_PITCH;
#ifdef __aarch64__
  create_params.memType = NVBUF_MEM_DEFAULT;
  create_params.memType = NVBUF_MEM_CUDA_UNIFIED;
  NvBufSurfaceCreate (&nvbuf, 1, &create_params);

  // Configure transform session parameters for the transformation
  transform_config_params.compute_mode = NvBufSurfTransformCompute_Default;
  transform_config_params.gpu_id = dsexample->gpu_id;
  transform_config_params.cuda_stream = dsexample->cuda_stream;

  // Set the transform session parameters for the conversions executed in this
  // thread.
  err = NvBufSurfTransformSetSessionParams (&transform_config_params);
  if (err != NvBufSurfTransformError_Success) {
        ("NvBufSurfTransformSetSessionParams failed with error %d", err), (NULL));
    goto error;

  // Calculate scaling ratio while maintaining aspect ratio
  ratio = MIN (1.0 * dest_width/ src_width, 1.0 * dest_height / src_height);

  if ((crop_rect_params->width == 0) || (crop_rect_params->height == 0)) {
        ("%s:crop_rect_params dimensions are zero",__func__), (NULL));
    goto error;

#ifdef __aarch64__
  if (ratio <= 1.0 / 16 || ratio >= 16.0) {
    // Currently cannot scale by ratio > 16 or < 1/16 for Jetson
    goto error;
  // Set the transform ROIs for source and destination
  src_rect = {(guint)src_top, (guint)src_left, (guint)src_width, (guint)src_height};
  dst_rect = {0, 0, (guint)dest_width, (guint)dest_height};

  // Set the transform parameters
  transform_params.src_rect = &src_rect;
  transform_params.dst_rect = &dst_rect;
  transform_params.transform_flag =
  transform_params.transform_filter = NvBufSurfTransformInter_Default;

  //Memset the memory
  NvBufSurfaceMemSet (nvbuf, 0, 0, 0);

  GST_DEBUG_OBJECT (dsexample, "Scaling and converting input buffer\n");

  // Transformation scaling+format conversion if any.
  err = NvBufSurfTransform (&ip_surf, nvbuf, &transform_params);
  if (err != NvBufSurfTransformError_Success) {
        ("NvBufSurfTransform failed with error %d while converting buffer", err),
    goto error;
  // Map the buffer so that it can be accessed by CPU
  if (NvBufSurfaceMap (nvbuf, 0, 0, NVBUF_MAP_READ) != 0){
    goto error;

  // Cache the mapped data for CPU access
  NvBufSurfaceSyncForCpu (nvbuf, 0, 0);

  // Use openCV to remove padding and convert RGBA to BGR. Can be skipped if
  // algorithm can handle padded RGBA data.
  in_mat =
      cv::Mat (dest_height, dest_width,
      CV_8UC4, nvbuf->surfaceList[0].mappedAddr.addr[0],
  out_mat =
      cv::Mat (cv::Size(dest_width, dest_height), CV_8UC3);

  cv::cvtColor (in_mat, out_mat, CV_RGBA2BGR);
  static gint dump = 0;
  if (dump < 150) {
      char filename[64];
      snprintf(filename, 64, "/home/nvidia/image%03d.jpg", dump);
      cv::imwrite(filename, out_mat);

  if (NvBufSurfaceUnMap (nvbuf, 0, 0)){
    goto error;

#ifdef __aarch64__
  // To use the converted buffer in CUDA, create an EGLImage and then use
  // CUDA-EGL interop APIs
    if (NvBufSurfaceMapEglImage (dsexample->inter_buf, 0) !=0 ) {
      goto error;

    // dsexample->inter_buf->surfaceList[0].mappedAddr.eglImage
    // Use interop APIs cuGraphicsEGLRegisterImage and
    // cuGraphicsResourceGetMappedEglFrame to access the buffer in CUDA

    // Destroy the EGLImage
    NvBufSurfaceUnMapEglImage (dsexample->inter_buf, 0);

  /* We will first convert only the Region of Interest (the entire frame or the
   * object bounding box) to RGB and then scale the converted RGB frame to
   * processing resolution. */
  return GST_FLOW_OK;

  return GST_FLOW_ERROR;

Figured it out. Thanks.

@sharanssundar Could you please share how you have added this?