Camera tampering using dsexample in jetson nano

Please provide complete information as applicable to your setup.

**• Hardware Platform (Jetson / GPU)**jetson nano
• DeepStream Version5.1
**• JetPack Version (valid for Jetson only)**4.5.1

Hi I have successfully added and tried with the tampering detection code using opencv in my dgpu Laptop without any fps reduction
But with nano I am seeing much reduction in fps(15 fps- 3fps)!! Can you recommend some changes to eliminate this
below is the code

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,NvDsBatchMeta *batch_meta,NvDsFrameMeta *frame_meta)
NvBufSurfTransform_Error err;
NvBufSurfTransformConfigParams transform_config_params;
NvBufSurfTransformParams transform_params;
NvBufSurfTransformRect src_rect;
NvBufSurfTransformRect dst_rect;
NvBufSurface ip_surf;


cv::Mat in_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((unsigned int)crop_rect_params->left);
gint src_top = GST_ROUND_UP_2((unsigned int)crop_rect_params->top);
gint src_width = GST_ROUND_DOWN_2((unsigned int)crop_rect_params->width);
gint src_height = GST_ROUND_DOWN_2((unsigned int)crop_rect_params->height);

/* Maintain aspect ratio */
double hdest = dsexample->processing_width * src_height / (double) src_width;
double wdest = dsexample->processing_height * src_width / (double) src_height;
guint dest_width, dest_height;

if (hdest <= dsexample->processing_height) {
dest_width = dsexample->processing_width;
dest_height = hdest;
} else {
dest_width = wdest;
dest_height = dsexample->processing_height;

/* 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));
    return GST_FLOW_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));

#ifdef aarch64
if (ratio <= 1.0 / 16 || ratio >= 16.0) {
/* Currently cannot scale by ratio > 16 or < 1/16 for Jetson /
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 (dsexample->inter_buf, 0, 0, 0);

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

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

/* Cache the mapped data for CPU access */
NvBufSurfaceSyncForCpu (dsexample->inter_buf, 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 (dsexample->processing_height, dsexample->processing_width,
    CV_8UC4, dsexample->inter_buf->surfaceList[0].mappedAddr.addr[0],

bg->apply(in_mat, fore);

erode (fore, fore, cv::Mat ());
erode (fore, fore, cv::Mat ());
dilate (fore, fore, cv::Mat ());
dilate (fore, fore, cv::Mat ());
dilate (fore, fore, cv::Mat ());

findContours (fore, contours,cv::RETR_EXTERNAL,cv::CHAIN_APPROX_SIMPLE);
int a=0;

std::vectorcv::Rect boundRect( contours.size() );
for( int it = 0; it < contours.size(); it++ )
boundRect[it] = boundingRect( contours[it] );
for( int it = 0; it< contours.size(); it++ )
if(boundRect[it].width>=40 || boundRect[it].height>=40)
//cout<<“Net contour area is “<<a<<”\n”;
// std::cout<<“camera tampering in camera”<<frame_meta->source_id<<“\n”;
cam_tamp = 1;

	  cam_tamp = 0;


//std::cout<<“camera source id:”<<frame_meta->source_id<<“\n”;

cv::cvtColor (in_mat, *dsexample->cvmat, cv::COLOR_RGBA2BGR);
cv::cvtColor (in_mat, *dsexample->cvmat, CV_RGBA2BGR);

if (NvBufSurfaceUnMap (dsexample->inter_buf, 0, 0)){

#ifdef aarch64
/* To use the converted buffer in CUDA, create an EGLImage and then use

  • CUDA-EGL interop APIs */
    if (USE_EGLIMAGE) {
    if (NvBufSurfaceMapEglImage (dsexample->inter_buf, 0) !=0 ) {
    return GST_FLOW_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;


This looks possible. OpenCV functions use CPU and comparing Jetson Nano to laptop, there is performance deviation. Please run sudo tegrastats to check system loading. If CPU cores are at full load, it has achieved maximum throughput.

How can I increase fps in nano to earlier rate?

how can I optimise my code for that

For further optimization, we would suggest shift the loading from CPU to GPU. You may refer to this patch:
How to create opencv gpumat from nvstream? - #18 by DaneLLL
And check if there is other APIs which can achieve the same function. If not, may need to implement CUDA code.

Can you please suggest an api for the same?

Please check if the function is supported in VPI:
VPI - Vision Programming Interface: Main Page
If yes, please refer to the patch for using VPI in DeepStream SDK:
Deepstream SDK + VPI on Jetson tx2 - #21 by AastaLLL

If there is no existing APIs, you would need to implement CUDA code.

Is there any way I could skip frames in ds example to increase fps? @DaneLLL

gst_dsexample_transform_ip() is called for every frame. If you don’t want to do processing to the frame, can return directly. For example, if the source is 30fps, you can do one, rerun one, … So that 15 frames are processed in one second.

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