opencv videocapture can't open MJPEG stream - linux

Question

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

Answer 1

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.