How to save frames from GstBuffer?

Dear supporter,

This question have confused me several days . I want to get the image data from GstBuffer after recognized. I have reference the function of gst_yoloplugin_transform_ip() and get_converted_mat().

My plotform is on TX2 deepstream 1.5 ,using gst-yoloplugin-tegra.

I added below code at the last function of attach_metadata_full_frame.
The recognized bbox have attached to GstBuffer(inbuf) by function gst_buffer_add_iva_meta_full,right?

It will have Segmentation fault error using below code,can you give me some suggeations for it.

My code:

dsmeta = gst_buffer_add_nvds_meta (inbuf, bbparams, free_ds_meta);
 dsmeta->meta_type = NVDS_META_FRAME_INFO;
//*****my code below******
	static gint coun=0;
	gchar file[100];
	cv::Mat save_in_mat,save_out_mat;
	gpointer state = NULL;
	GstMeta *gst_meta = NULL;
	NvBufferParams buf_params;

	GstMapInfo in_map_info;
	int in_dmabuf_fd = 0;

	gpointer mapped_ptr = NULL;
	GstFlowReturn flow_ret = GST_FLOW_OK;

	memset (&in_map_info, 0, sizeof (in_map_info));
	if (!gst_buffer_map (inbuf, &in_map_info, GST_MAP_READ)) {
    flow_ret = GST_FLOW_ERROR;
    goto done;

	if (ExtractFdFromNvBuffer (, &in_dmabuf_fd)) {
	  flow_ret = GST_FLOW_ERROR;
	  goto done;

	for (guint i = 0; i < batch_size; i++) {

	  if (NvBufferGetParams (in_dmabuf_fd, &buf_params) != 0) {
	    flow_ret = GST_FLOW_ERROR;
	    goto done;

		//NvBufferGetParams (in_dmabuf_fd, &buf_params);
		if (NvBufferMemMap(in_dmabuf_fd, 0, NvBufferMem_Read,&mapped_ptr) != 0) {
			    flow_ret = GST_FLOW_ERROR;
    goto done;

		//cv::imwrite(file, batchBlob);
		//GstBuffer *buf = (GstBuffer *) inbuf->data;

		GstMapInfo map;
		//gst_buffer_map (inbuf, &map, GST_MAP_READ);
		gint width=1280;
		gint height=720;

		save_in_mat=cv::Mat (width, height, CV_8UC4, mapped_ptr, buf_params.pitch[0]);//cv::Mat::AUTO_STEP
		cv::cvtColor (save_in_mat, save_out_mat, CV_BGRA2BGR);

		cv::imwrite(file, save_out_mat);
	  if (mapped_ptr){
	    NvBufferMemUnMap (in_dmabuf_fd, 0, &mapped_ptr);
	  if (in_dmabuf_fd){
    	NvReleaseFd (in_dmabuf_fd);
  	  gst_buffer_unmap (inbuf, &in_map_info);
	  std::cout << "debug save image " <<":done end!"<< std::endl;
	 //return flow_ret;

For more information, please check which line hits segment fault.

Hi 15822004929,

We have released the DeepSteam SDK 4.0 at last week, please migrate to this new version for more features and supports, see