the Opencv 2.4.9: VideoCapture cann't open the MJPG-streamer:
VideoCapture cap; cap.open("http://127.0.0.1:8080/?action=stream&type=.mjpg"); if (!cap.isOpened()) // if not success, exit program { cout << "Cannot open the video cam" << endl; return -1; }
I can see the video use gst-launch. and I have searched a lot,like this and tried the fifo like this,but still cann't open it.
then I want to debug into opencv,compile opencv with CMAKE_BUILD_TYPE=DEBUG, but my GDB just cann't step into the open function.any idea?
my makefile:
OpencvDebugLibDir=/home/ry/lib CFLAGS = -g -I$(OpencvDebugLibDir)/include/opencv -I$(OpencvDebugLibDir) LIBS = $(OpencvDebugLibDir)/lib/*.so target : main.cpp g++ $(CFLAGS) $(LIBS) -o $@ $<
by the way, I am in opensue13.1, with the same code,I can open the video in win 7.
thank you.
Update now I can step into some function like:imshow,waitKey, but I can not step into others like:imread,namedWindow,it shows:
29 image = cv::imread(name); (gdb) s std::allocator<char>::allocator (this=0x7fffffffdc7f) at /usr/src/debug/gcc-4.8.1-20130909/obj-x86_64-suse-linux/x86_64-suse-linux/libstdc++-v3/include/bits/allocator.h:113 113 allocator() throw() { }
test4.cpp:
#include <stdio.h> #include <opencv2/opencv.hpp> using namespace cv; int main(int argc, char** argv ) { Mat image; image = imread( "LinuxLogo.jpg", 1 ); if ( !image.data ) { printf("No image data \n"); return -1; } namedWindow("Display Image", CV_WINDOW_AUTOSIZE ); imshow("Display Image", image); waitKey(0); return 0; }
my makefile:
OpencvDebugLibDir=/home/ry/lib CFLAGS=-g -I$(OpencvDebugLibDir)/include/opencv -I$(OpencvDebugLibDir) LIBS=$(OpencvDebugLibDir)/lib test4:test4.cpp g++ $(CFLAGS) -o $@ $< -L$(LIBS) -lopencv_highgui -lopencv_core -Wl,-rpath=/home/ry/lib/lib
run gdb:
gdb test4 -d /home/ry/learn/opencv/install/OpenCV/opencv-2.4.9/modules/core/src -d /home/ry/learn/opencv/install/OpenCV/opencv-2.4.9/modules/highgui/src
opencv videocapture can't open MJPEG stream,because I don't compile opencv with FFMPEG support. detail: when cmake the opencv:
cmake -D CMAKE_BUILD_TYPE=RELEASE -D CMAKE_INSTALL_PREFIX=/usr/local -D BUILD_SHARED_LIBS=ON -D WITH_TBB=ON -D WITH_OPENMP=ON -D WITH_OPENCL=ON -D WITH_CUDA=ON -D WITH_GTK=ON -D BUILD_NEW_PYTHON_SUPPORT=ON -D WITH_V4L=ON -D INSTALL_C_EXAMPLES=OFF -D INSTALL_PYTHON_EXAMPLES=OFF -D BUILD_EXAMPLES=OFF -D WITH_QT=ON -D WITH_OPENGL=ON -D BUILD_JPEG=ON -D BUILD_PNG=ON -D BUILD_JASPER=ON -D BUILD_ZLIB=ON -D WITH_JPEG=ON -D WITH_PNG=ON -D WITH_JASPER=ON -D WITH_ZLIB=ON -D WITH_OPENEXR=OFF ..
you get something like:
FFMPEG: NO -- codec: NO -- format: NO -- util: NO -- swscale: NO -- gentoo-style: NO
so the cmake don't find the FFMPEG. I should install libffmpeg-devel in my machine(Opensuse 13.1),then the pkg-config can find FFMPEG,you can check with this:
pkg-config --list-all | grep libavcodec
then run the above cmake command again, I get:
FFMPEG: YES -- codec: YES (ver 55.69.100) -- format: YES (ver 55.48.100) -- util: YES (ver 52.92.100) -- swscale: YES (ver 2.6.100) -- gentoo-style: YES
make,and I get the opencv videocapture able to open MJPG_Streamer.
PS:to find the reason,I compile a debug version opencv,and step into the VideoCapture's open function,and in the construction function of icvInitFFMPEG() in " opencv-2.4.9/modules/highgui/src/cap.cpp ":
#elif defined HAVE_FFMPEG icvCreateFileCapture_FFMPEG_p = (CvCreateFileCapture_Plugin)cvCreateFileCapture_FFMPEG; icvReleaseCapture_FFMPEG_p = (CvReleaseCapture_Plugin)cvReleaseCapture_FFMPEG; icvGrabFrame_FFMPEG_p = (CvGrabFrame_Plugin)cvGrabFrame_FFMPEG; icvRetrieveFrame_FFMPEG_p = (CvRetrieveFrame_Plugin)cvRetrieveFrame_FFMPEG; icvSetCaptureProperty_FFMPEG_p = (CvSetCaptureProperty_Plugin)cvSetCaptureProperty_FFMPEG; icvGetCaptureProperty_FFMPEG_p = (CvGetCaptureProperty_Plugin)cvGetCaptureProperty_FFMPEG; icvCreateVideoWriter_FFMPEG_p = (CvCreateVideoWriter_Plugin)cvCreateVideoWriter_FFMPEG; icvReleaseVideoWriter_FFMPEG_p = (CvReleaseVideoWriter_Plugin)cvReleaseVideoWriter_FFMPEG; icvWriteFrame_FFMPEG_p = (CvWriteFrame_Plugin)cvWriteFrame_FFMPEG; #endif
it just step over these code,so I know because I don't have the HAVE_FFMPEG defined in compiling process.
