Aquí está mi solución completa de código fuente para Gstreamer 1.4.0 y OpenCV 2.4.9.
Utiliza gst_parse_launch() para analizar la línea de comando normal que le daría al gst-launch. Gstreamer pipeline convierte las tramas al formato RGB888 antes de alimentarlas a OpenCV para que la conversión sea lo más fácil posible.
El procesamiento de tramas OpenCV no se realiza en la devolución de llamada new_sample(), pero solo toma el marco de gstreamer y lo empuja a la cola, que luego se consumirá en el hilo principal. De esta manera, podemos llamar, p. imshow() desde OpenCV para renderizar imagen a pantalla.
~ 150 líneas ... eliminando las impresiones de depuración, etc. podría reducirse a < 100 líneas de código.
Probablemente habría que añadir que hay sincronización de hilo alrededor de lectura deque/escritura
#include <gst/gst.h>
#include <gst/app/gstappsink.h>
#include <stdlib.h>
#include "opencv2/opencv.hpp"
using namespace cv;
// TODO: use synchronized deque
std::deque<Mat> frameQueue;
GstFlowReturn
new_preroll(GstAppSink *appsink, gpointer data) {
g_print ("Got preroll!\n");
return GST_FLOW_OK;
}
GstFlowReturn
new_sample(GstAppSink *appsink, gpointer data) {
static int framecount = 0;
framecount++;
GstSample *sample = gst_app_sink_pull_sample(appsink);
GstCaps *caps = gst_sample_get_caps(sample);
GstBuffer *buffer = gst_sample_get_buffer(sample);
const GstStructure *info = gst_sample_get_info(sample);
// ---- Read frame and convert to opencv format ---------------
GstMapInfo map;
gst_buffer_map (buffer, &map, GST_MAP_READ);
// convert gstreamer data to OpenCV Mat, you could actually
// resolve height/width from caps...
Mat frame(Size(320, 240), CV_8UC3, (char*)map.data, Mat::AUTO_STEP);
int frameSize = map.size;
// TODO: synchronize this....
frameQueue.push_back(frame);
gst_buffer_unmap(buffer, &map);
// ------------------------------------------------------------
// print dot every 30 frames
if (framecount%30 == 0) {
g_print (".");
}
// show caps on first frame
if (framecount == 1) {
g_print ("%s\n", gst_caps_to_string(caps));
}
gst_sample_unref (sample);
return GST_FLOW_OK;
}
static gboolean
my_bus_callback (GstBus *bus, GstMessage *message, gpointer data) {
g_print ("Got %s message\n", GST_MESSAGE_TYPE_NAME (message));
switch (GST_MESSAGE_TYPE (message)) {
case GST_MESSAGE_ERROR: {
GError *err;
gchar *debug;
gst_message_parse_error (message, &err, &debug);
g_print ("Error: %s\n", err->message);
g_error_free (err);
g_free (debug);
break;
}
case GST_MESSAGE_EOS:
/* end-of-stream */
break;
default:
/* unhandled message */
break;
}
/* we want to be notified again the next time there is a message
* on the bus, so returning TRUE (FALSE means we want to stop watching
* for messages on the bus and our callback should not be called again)
*/
return TRUE;
}
int
main (int argc, char *argv[])
{
GError *error = NULL;
gst_init (&argc, &argv);
gchar *descr = g_strdup(
"videotestsrc pattern=ball ! "
"video/x-raw,format=RGB ! "
"videoconvert ! "
"appsink name=sink sync=true"
);
GstElement *pipeline = gst_parse_launch (descr, &error);
if (error != NULL) {
g_print ("could not construct pipeline: %s\n", error->message);
g_error_free (error);
exit (-1);
}
/* get sink */
GstElement *sink = gst_bin_get_by_name (GST_BIN (pipeline), "sink");
gst_app_sink_set_emit_signals((GstAppSink*)sink, true);
gst_app_sink_set_drop((GstAppSink*)sink, true);
gst_app_sink_set_max_buffers((GstAppSink*)sink, 1);
GstAppSinkCallbacks callbacks = { NULL, new_preroll, new_sample };
gst_app_sink_set_callbacks (GST_APP_SINK(sink), &callbacks, NULL, NULL);
GstBus *bus;
guint bus_watch_id;
bus = gst_pipeline_get_bus (GST_PIPELINE (pipeline));
bus_watch_id = gst_bus_add_watch (bus, my_bus_callback, NULL);
gst_object_unref (bus);
gst_element_set_state (GST_ELEMENT (pipeline), GST_STATE_PLAYING);
namedWindow("edges",1);
while(1) {
g_main_iteration(false);
// TODO: synchronize...
if (frameQueue.size() > 0) {
// this lags pretty badly even when grabbing frames from webcam
Mat frame = frameQueue.front();
Mat edges;
cvtColor(frame, edges, CV_RGB2GRAY);
GaussianBlur(edges, edges, Size(7,7), 1.5, 1.5);
Canny(edges, edges, 0, 30, 3);
imshow("edges", edges);
cv::waitKey(30);
frameQueue.clear();
}
}
gst_element_set_state (GST_ELEMENT (pipeline), GST_STATE_NULL);
gst_object_unref (GST_OBJECT (pipeline));
return 0;
}
Para compilar en OSX/Linux hacer archivo como este debería hacer:
GST_FLAGS=$(shell pkg-config --cflags --libs gstreamer-gl-1.0 gstreamer-tag-1.0 gstreamer-net-1.0 gstreamer-sdp-1.0 \
gstreamer-1.0 gstreamer-allocators-1.0 gstreamer-insertbin-1.0 gstreamer-plugins-base-1.0 \
gstreamer-codecparsers-1.0 gstreamer-base-1.0 gstreamer-app-1.0 gstreamer-check-1.0 \
gstreamer-controller-1.0 gstreamer-video-1.0 gstreamer-fft-1.0 gstreamer-mpegts-1.0 \
gstreamer-pbutils-1.0 gstreamer-rtp-1.0 gstreamer-rtsp-1.0 \
gstreamer-riff-1.0 gstreamer-audio-1.0 gstreamer-plugins-bad-1.0 opencv)
OPENCV_FLAGS=$(shell pkg-config --cflags --libs opencv)
all: gst_opencv
gst_opencv: gst_opencv
g++ $(GST_FLAGS) $(OPENCV_FLAGS) gst_opencv -o gst_opencv
clean:
rm -f gst_opencv