OpenCV VideoCapture failed to open a file, how to determine reason? - opencv

Question

Using C++ OpenCV I was just trying to open a video file in Cygwin environment. For some reason file is not getting opened i.e. isOpened() is always false.
I checked for "ffmpeg -codecs" output within cygwin and it displays all available video codecs.
Video exists in the directory and I verified physically
Still unable to open the video file. To debug this issue can I see the error number that get set when videocapture fails to open the file.
#include <opencv2/opencv.hpp>
#include <iostream>
int main( int argc, char* argv[] ) {
//Tried with both namedWindow and without namedWindow command
//cv::namedWindow( "Video", cv::WINDOW_AUTOSIZE );
cv::VideoCapture capture( argv[1], cv::CAP_FFMPEG );
if (!capture.isOpened())
{
std::cout << "Unable to open the file " << argv[1] << std::endl;
**std::cout << "Reason for catpure fails is " << ???????**
exit(0);
}
std::cout << "Opened " << argv[1] << std::endl;
capture.release();
}
Note : I have not installed ffmpeg in cygwin environment. Instead I have ffmpeg in my Windows 10 and I had included the same in my Windows PATH environment. Within cygwin I am able to execute ffmpeg command
General configuration for OpenCV 3.4.1 =====================================
Version control: unknown
Platform:
Timestamp: 2021-01-19T11:33:15Z
Host: CYGWIN 3.1.7(0.340/5/3) x86_64
CMake: 3.17.3
CMake generator: Ninja
CMake build tool: /usr/bin/ninja.exe
Configuration: RelWithDebInfo
CPU/HW features:
Baseline: SSE SSE2 SSE3
requested: SSE3
Dispatched code generation: SSE4_1 SSE4_2 FP16 AVX AVX2 AVX512_SKX
requested: SSE4_1 SSE4_2 AVX FP16 AVX2 AVX512_SKX
SSE4_1 (3 files): + SSSE3 SSE4_1
SSE4_2 (1 files): + SSSE3 SSE4_1 POPCNT SSE4_2
FP16 (2 files): + SSSE3 SSE4_1 POPCNT SSE4_2 FP16 AVX
AVX (4 files): + SSSE3 SSE4_1 POPCNT SSE4_2 AVX
AVX2 (8 files): + SSSE3 SSE4_1 POPCNT SSE4_2 FP16 FMA3 AVX AVX2
AVX512_SKX (0 files): + SSSE3 SSE4_1 POPCNT SSE4_2 FP16 FMA3 AVX AVX2 AVX_512F AVX512_SKX
C/C++:
Built as dynamic libs?: YES
C++11: YES
C++ Compiler: /usr/bin/g++.exe (ver 10.2.0)
C++ flags (Release): -fpermissive -fsigned-char -W -Wall -Werror=return-type -Werror=non-virtual-dtor -Werror=address -Werror=sequence-point -Wformat -Werror=format-security -Wmissing-declarations -Wmissing-prototypes -Wstrict-prototypes -Wundef -Winit-self -Wpointer-arith -Wshadow -Wsign-promo -Wuninitialized -Winit-self -Wno-narrowing -Wno-delete-non-virtual-dtor -Wno-comment -Wno-implicit-fallthrough -fdiagnostics-show-option -Wno-long-long -pthread -fomit-frame-pointer -ffunction-sections -fdata-sections -msse -msse2 -msse3 -fvisibility=hidden -fvisibility-inlines-hidden -O3 -DNDEBUG -DNDEBUG
C++ flags (Debug): -fpermissive -fsigned-char -W -Wall -Werror=return-type -Werror=non-virtual-dtor -Werror=address -Werror=sequence-point -Wformat -Werror=format-security -Wmissing-declarations -Wmissing-prototypes -Wstrict-prototypes -Wundef -Winit-self -Wpointer-arith -Wshadow -Wsign-promo -Wuninitialized -Winit-self -Wno-narrowing -Wno-delete-non-virtual-dtor -Wno-comment -Wno-implicit-fallthrough -fdiagnostics-show-option -Wno-long-long -pthread -fomit-frame-pointer -ffunction-sections -fdata-sections -msse -msse2 -msse3 -fvisibility=hidden -fvisibility-inlines-hidden -g -O0 -DDEBUG -D_DEBUG
C Compiler: /usr/bin/gcc.exe
C flags (Release): -ggdb -O2 -pipe -Wall -Werror=format-security -Wp,-D_FORTIFY_SOURCE=2 -fstack-protector-strong --param=ssp-buffer-size=4 -fdebug-prefix-map=/pub/devel/opencv/v3.4/opencv-3.4.1-3.x86_64/build=/usr/src/debug/opencv-3.4.1-3 -fdebug-prefix-map=/pub/devel/opencv/v3.4/opencv-3.4.1-3.x86_64/src/opencv-3.4.1=/usr/src/debug/opencv-3.4.1-3 -fsigned-char -W -Wall -Werror=return-type -Werror=non-virtual-dtor -Werror=address -Werror=sequence-point -Wformat -Werror=format-security -Wmissing-declarations -Wmissing-prototypes -Wstrict-prototypes -Wundef -Winit-self -Wpointer-arith -Wshadow -Wsign-promo -Wuninitialized -Winit-self -Wno-narrowing -Wno-delete-non-virtual-dtor -Wno-comment -Wno-implicit-fallthrough -fdiagnostics-show-option -Wno-long-long -pthread -fomit-frame-pointer -ffunction-sections -fdata-sections -msse -msse2 -msse3 -fvisibility=hidden -fvisibility-inlines-hidden -O3 -DNDEBUG -DNDEBUG
C flags (Debug): -ggdb -O2 -pipe -Wall -Werror=format-security -Wp,-D_FORTIFY_SOURCE=2 -fstack-protector-strong --param=ssp-buffer-size=4 -fdebug-prefix-map=/pub/devel/opencv/v3.4/opencv-3.4.1-3.x86_64/build=/usr/src/debug/opencv-3.4.1-3 -fdebug-prefix-map=/pub/devel/opencv/v3.4/opencv-3.4.1-3.x86_64/src/opencv-3.4.1=/usr/src/debug/opencv-3.4.1-3 -fsigned-char -W -Wall -Werror=return-type -Werror=non-virtual-dtor -Werror=address -Werror=sequence-point -Wformat -Werror=format-security -Wmissing-declarations -Wmissing-prototypes -Wstrict-prototypes -Wundef -Winit-self -Wpointer-arith -Wshadow -Wsign-promo -Wuninitialized -Winit-self -Wno-narrowing -Wno-delete-non-virtual-dtor -Wno-comment -Wno-implicit-fallthrough -fdiagnostics-show-option -Wno-long-long -pthread -fomit-frame-pointer -ffunction-sections -fdata-sections -msse -msse2 -msse3 -fvisibility=hidden -fvisibility-inlines-hidden -g -O0 -DDEBUG -D_DEBUG
Linker flags (Release):
Linker flags (Debug):
ccache: NO
Precompiled headers: NO
Extra dependencies: dl m pthread rt
3rdparty dependencies:
OpenCV modules:
To be built: aruco bgsegm bioinspired calib3d ccalib core datasets dpm face features2d flann freetype fuzzy hdf hfs highgui img_hash imgcodecs imgproc java_bindings_generator line_descriptor ml objdetect optflow phase_unwrapping photo plot python2 python3 python_bindings_generator reg rgbd saliency shape stereo stitching structured_light superres surface_matching tracking ts video videoio videostab ximgproc xobjdetect xphoto
Disabled: dnn js world
Disabled by dependency: dnn_objdetect text
Unavailable: cnn_3dobj cudaarithm cudabgsegm cudacodec cudafeatures2d cudafilters cudaimgproc cudalegacy cudaobjdetect cudaoptflow cudastereo cudawarping cudev cvv dnn_modern java matlab ovis sfm viz
Applications: tests apps
Documentation: NO
Non-free algorithms: NO
GUI:
GTK+: YES (ver 3.22.28)
GThread : YES (ver 2.54.3)
GtkGlExt: NO
VTK support: NO
Media I/O:
ZLib: /lib/libz.dll.a (ver 1.2.11)
JPEG: /lib/libjpeg.dll.a (ver )
WEBP: /lib/libwebp.dll.a (ver encoder: 0x020e)
PNG: /lib/libpng.dll.a (ver 1.6.37)
TIFF: /lib/libtiff.dll.a (ver 42 / 4.2.0)
JPEG 2000: /lib/libjasper.dll.a (ver 2.0.14)
OpenEXR: build (ver 1.7.1)
Video I/O:
GStreamer:
base: YES (ver 1.12.5)
video: YES (ver 1.12.5)
app: YES (ver 1.12.5)
riff: YES (ver 1.12.5)
pbutils: YES (ver 1.12.5)
gPhoto2: NO
Parallel framework: pthreads
Trace: YES (with Intel ITT)
Other third-party libraries:
Lapack: NO
Eigen: YES (ver 3.3.9)
Custom HAL: NO
Protobuf: build (3.5.1)
NVIDIA CUDA: NO
OpenCL: YES (no extra features)
Include path: /usr/include/CL
Link libraries: Dynamic load
Python 2:
Interpreter: /usr/bin/python2.7.exe (ver 2.7.18)
Libraries: /lib/libpython2.7.dll.a (ver 2.7.18)
numpy: /usr/lib/python2.7/site-packages/numpy/core/include (ver 1.16.2)
packages path: lib/python2.7/site-packages
Python 3:
Interpreter: /usr/bin/python3 (ver 3.8.7)
Libraries: /lib/libpython3.8.dll.a (ver 3.8.7)
numpy: /usr/lib/python3.8/site-packages/numpy/core/include (ver 1.19.4)
packages path: lib/python3.8/site-packages
Python (for build): /usr/bin/python2.7.exe
Java:
ant: NO
JNI: NO
Java wrappers: NO
Java tests: NO
Matlab: NO
Install to: /usr
-----------------------------------------------------------------