Convert CvMat to GstBuffer

[Florian Echtler]

I'd recommend using gst_buffer_new_wrapped_full instead, that saves a buffer
copy. Here's an example I'm using with appsrc which works fine (warning:
hardcoded buffer size):


void buffer_destroy(gpointer data) {
  cv::Mat* done = (cv::Mat*)data;
  delete done;
}

GstFlowReturn prepare_buffer(GstAppSrc* appsrc, cv::Mat* frame) {

  guint size = 1280 * 720 * 4;
  GstBuffer *buffer = gst_buffer_new_wrapped_full( (GstMemoryFlags)0,
(gpointer)(frame->data), size, 0, size, frame, buffer_destroy );

  return gst_app_src_push_buffer(appsrc, buffer);
}


Best regards, Florian


On 09.06.2017 00:34, raomayurs wrote:
> Hi,
> I am a newbie to gstreamer plugin development. I am trying to create a
> plugin using the tool provided by gstreamer. I am following the plugin
> writer's guide. I am trying to process data in the _chain function. I was
> able to successfully extract the video frame from GstBuffer and do my
> processing using openCV. But now I am unable to reconvert CvMat into
> GstBuffer.
> 
> Here is my code:
> 
> GBuffer* process_data(GstPad *sinkPad, GstMyFilter *filter, GstBuffer *buf)
> {
>  //Get Height and width of input frame
>   gint gheight, gwidth;
>   static GstClockTime timestamp = 0;
>   int height, width, channels = 3;
>   GstCaps *caps = gst_pad_get_current_caps(sinkPad);
>   GstStructure *str = gst_caps_get_structure (caps, 0);
>   if (!gst_structure_get_int (str, "width", &gwidth)) {
>     width = 1280;
>   } else {
>     width = (int) gwidth;
>   }
>   if (!gst_structure_get_int (str, "height", &gheight)) {
>     height = 720;
>   } else {
>     height = (int) gheight;
>   }
> 
> // convert buffer to opencv mat
>   GstMapInfo map;
>   gst_buffer_map (buf, &map, GST_MAP_READ); 
>   CvMat frame_yuv = cvMat(height + height/2, width, CV_8UC1, map.data);
>   CvMat *frame = cvCreateMat(height, width, CV_8UC3);
>   cvCvtColor(&frame_yuv, frame, CV_YUV2RGB_YV12);
> 
> // Process frame  
>   CvMat *r = cvCreateMat(height, width, CV_8UC1);
>   CvMat *g = cvCreateMat(height, width, CV_8UC1);
>   CvMat *b = cvCreateMat(height, width, CV_8UC1);
> 
>   CvMat cameraMatrix = cvMat(3, 3, CV_64F, filter->cameraMatrix);                                                                                                                                                                                       
>   CvMat distortionCoefficients = cvMat(5, 1, CV_64F,
> filter->distortionCoefficients);
>   CvMat *newcamera_matrix = cvCreateMat(3, 3, CV_64F);
>   CvMat *r1 = cvCreateMat(height, width, CV_8UC1);
>   CvMat *g1 = cvCreateMat(height, width, CV_8UC1);
>   CvMat *b1 = cvCreateMat(height, width, CV_8UC1);
>   CvMat *undistorted = cvCreateMat(height, width, CV_8UC3);
>   CvSize imgSize = cvSize(width, height);
>   cvGetOptimalNewCameraMatrix(&cameraMatrix, &distortionCoefficients,
> imgSize, 1.0, newcamera_matrix, imgSize, NULL, 0);
>   cvSplit(frame, r,g,b, NULL);
>   cvUndistort2(r, r1, &cameraMatrix, &distortionCoefficients,
> newcamera_matrix);
>   cvUndistort2(g, g1, &cameraMatrix, &distortionCoefficients,
> newcamera_matrix);
>   cvUndistort2(b, b1, &cameraMatrix, &distortionCoefficients,
> newcamera_matrix);
>   cvMerge(1r,g1,b1, NULL, undistorted);
> 
> //reconvert processed cvMat into GstBuffer
>   GstMapInfo mapinfo;
>   GstBuffer *buffer;
>   gint size = height * width * channels;
>   buffer = gst_buffer_new_allocate (NULL, size, NULL);
>   gst_buffer_map (buffer, &mapinfo, GST_MAP_WRITE);
>   memcpy( (guchar *)map.data, (guchar *)&(undistorted->data), 
> gst_buffer_get_size( buffer ) );
>   GST_BUFFER_PTS (buffer) = timestamp;
>   GST_BUFFER_DURATION (buffer) = gst_util_uint64_scale_int (1, GST_SECOND,
> 2);
> 
>   timestamp += GST_BUFFER_DURATION (buffer);
>   return buffer;
> }
> 
> The returned buffer is passed to the src pad of the filter. The above code
> is not creating the buffer correctly. Am I converting cvMat to GstBuffer
> correctly? Because the openCV part is working correctly. The undistorted
> matrix is as expected. But the conversion to GstBuffer is failing for some
> reason. Any help will be really appreciated. 
> 
> Thanks
> 
> 
> 
> --
> View this message in context: http://gstreamer-devel.966125.n4.nabble.com/Convert-CvMat-to-GstBuffer-tp4683259.html
> Sent from the GStreamer-devel mailing list archive at Nabble.com.
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> gstreamer-devel mailing list
> gstreamer-devel at lists.freedesktop.org
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> 


-- 
SENT FROM MY DEC VT50 TERMINAL

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