OpenCV VideoCapture() doesn't work - Ubuntu - c++

Question

OpenCV 4.5 - Ubuntu - Jetson Nano 2GB
Hello I have a problem with getting video from my webcam (connected by USB to JetsonNano) by OpenCV
Here's my code:
// cv::VideoCapture cap( ... );
cv::Mat frame;
if (!cap.isOpened()) // if not success, exit program
{
cout << "Cannot open the video cam" << endl;
return -1;
}
cv::namedWindow("test", cv::WINDOW_AUTOSIZE);
while(true)
{
try
{
cap >> frame;
cv::imshow("test", frame);
}
catch(const std::exception& e)
{
std::cerr << e.what() << '\n';
}
}
1 | cv::VideoCapture cap(0) gives me:
[ WARN:0] global /home/legion/opencv/modules/videoio/src/cap_gstreamer.cpp (935) open OpenCV | GStreamer warning: Cannot query video position: status=0, value=-1, duration=-1
2 | cv::VideoCapture cap("/dev/video0") gives me:
[ WARN:0] global /home/legion/opencv/modules/videoio/src/cap_gstreamer.cpp (1761) handleMessage OpenCV | GStreamer warning: Embedded video playback halted; module source reported: Could not read from resource.
[ WARN:0] global /home/legion/opencv/modules/videoio/src/cap_gstreamer.cpp (888) open OpenCV | GStreamer warning: unable to start pipeline
[ WARN:0] global /home/legion/opencv/modules/videoio/src/cap_gstreamer.cpp (480) isPipelinePlaying OpenCV | GStreamer warning: GStreamer: pipeline have not been created
Cannot open the video cam
3 | When I try to open camera by command, only this one work:
$ gst-launch-1.0 v4l2src device=\"/dev/video0\" ! xvimagesink
I gave it a try:
cv::VideoCapture cap("v4l2src device=\"/dev/video0\" ! xvimagesink") it gives me:
[ WARN:0] global /home/legion/opencv/modules/videoio/src/cap_gstreamer.cpp (803) open OpenCV | GStreamer warning: cannot find appsink in manual pipeline
[ WARN:0] global /home/legion/opencv/modules/videoio/src/cap_gstreamer.cpp (480) isPipelinePlaying OpenCV | GStreamer warning: GStreamer: pipeline have not been created
Cannot open the video cam
If I gave other sinks : autosink or appsink, it's also doesn't work.
4 | I tried the solution from that link
https://forums.developer.nvidia.com/t/sony-camera-module-cannot-be-opened-with-opencv-on-xavier/84003
cv::VideoCapture cap("v4l2src device=/dev/video0 ! video/x-raw,width=1920,height=1080,format=UYVY,framerate=30/1 ! videoconvert ! video/x-raw,format=BGR ! appsink") and it's gives me :
[ WARN:0] global /home/legion/opencv/modules/videoio/src/cap_gstreamer.cpp (1761) handleMessage OpenCV | GStreamer warning: Embedded video playback halted; module v4l2src0 reported: Internal data stream error.
[ WARN:0] global /home/legion/opencv/modules/videoio/src/cap_gstreamer.cpp (888) open OpenCV | GStreamer warning: unable to start pipeline
[ WARN:0] global /home/legion/opencv/modules/videoio/src/cap_gstreamer.cpp (480) isPipelinePlaying OpenCV | GStreamer warning: GStreamer: pipeline have not been created
[ERROR:0] global /home/legion/opencv/modules/videoio/src/cap.cpp (142) open VIDEOIO(CV_IMAGES): raised OpenCV exception:
OpenCV(4.5.0) /home/legion/opencv/modules/videoio/src/cap_images.cpp:253: error: (-5:Bad argument) CAP_IMAGES: can't find starting number (in the name of file): v4l2src device=/dev/video0 ! video/x-raw,width=1920,height=1080,format=UYVY,framerate=30/1 ! videoconvert ! video/x-raw,format=BGR ! appsink in function 'icvExtractPattern'
Someone knows what's going on and how to fix it?
Edit#1:
My OpenCV buildinfo :
General configuration for OpenCV 4.5.0 =====================================
Version control: unknown
Extra modules:
Location (extra): /home/legion/opencv_contrib/modules
Version control (extra): unknown
Platform:
Timestamp: 2020-11-24T13:09:24Z
Host: Linux 4.9.140-tegra aarch64
CMake: 3.10.2
CMake generator: Unix Makefiles
CMake build tool: /usr/bin/make
Configuration: RELEASE
CPU/HW features:
Baseline: NEON FP16
required: NEON
disabled: VFPV3
C/C++:
Built as dynamic libs?: YES
C++ standard: 11
C++ Compiler: /usr/bin/c++ (ver 7.5.0)
C++ flags (Release): -fsigned-char -ffast-math -W -Wall -Werror=return-type -Werror=non-virtual-dtor -Werror=address -Werror=sequence-point -Wformat -Werror=format-security -Wmissing-declarations -Wundef -Winit-self -Wpointer-arith -Wshadow -Wsign-promo -Wuninitialized -Winit-self -Wsuggest-override -Wno-delete-non-virtual-dtor -Wno-comment -Wimplicit-fallthrough=3 -Wno-strict-overflow -fdiagnostics-show-option -pthread -fomit-frame-pointer -ffunction-sections -fdata-sections -fvisibility=hidden -fvisibility-inlines-hidden -fopenmp -O3 -DNDEBUG -DNDEBUG
C++ flags (Debug): -fsigned-char -ffast-math -W -Wall -Werror=return-type -Werror=non-virtual-dtor -Werror=address -Werror=sequence-point -Wformat -Werror=format-security -Wmissing-declarations -Wundef -Winit-self -Wpointer-arith -Wshadow -Wsign-promo -Wuninitialized -Winit-self -Wsuggest-override -Wno-delete-non-virtual-dtor -Wno-comment -Wimplicit-fallthrough=3 -Wno-strict-overflow -fdiagnostics-show-option -pthread -fomit-frame-pointer -ffunction-sections -fdata-sections -fvisibility=hidden -fvisibility-inlines-hidden -fopenmp -g -O0 -DDEBUG -D_DEBUG
C Compiler: /usr/bin/cc
C flags (Release): -fsigned-char -ffast-math -W -Wall -Werror=return-type -Werror=address -Werror=sequence-point -Wformat -Werror=format-security -Wmissing-declarations -Wmissing-prototypes -Wstrict-prototypes -Wundef -Winit-self -Wpointer-arith -Wshadow -Wuninitialized -Winit-self -Wno-comment -Wimplicit-fallthrough=3 -Wno-strict-overflow -fdiagnostics-show-option -pthread -fomit-frame-pointer -ffunction-sections -fdata-sections -fvisibility=hidden -fopenmp -O3 -DNDEBUG -DNDEBUG
C flags (Debug): -fsigned-char -ffast-math -W -Wall -Werror=return-type -Werror=address -Werror=sequence-point -Wformat -Werror=format-security -Wmissing-declarations -Wmissing-prototypes -Wstrict-prototypes -Wundef -Winit-self -Wpointer-arith -Wshadow -Wuninitialized -Winit-self -Wno-comment -Wimplicit-fallthrough=3 -Wno-strict-overflow -fdiagnostics-show-option -pthread -fomit-frame-pointer -ffunction-sections -fdata-sections -fvisibility=hidden -fopenmp -g -O0 -DDEBUG -D_DEBUG
Linker flags (Release): -Wl,--gc-sections -Wl,--as-needed
Linker flags (Debug): -Wl,--gc-sections -Wl,--as-needed
ccache: NO
Precompiled headers: NO
Extra dependencies: m pthread cudart_static dl rt nppc nppial nppicc nppicom nppidei nppif nppig nppim nppist nppisu nppitc npps cublas cudnn cufft -L/usr/local/cuda/lib64 -L/usr/lib/aarch64-linux-gnu
3rdparty dependencies:
OpenCV modules:
To be built: alphamat aruco bgsegm bioinspired calib3d ccalib core cudaarithm cudabgsegm cudacodec cudafeatures2d cudafilters cudaimgproc cudalegacy cudaobjdetect cudaoptflow cudastereo cudawarping cudev datasets dnn dnn_objdetect dnn_superres dpm face features2d flann freetype fuzzy gapi hdf hfs highgui img_hash imgcodecs imgproc intensity_transform line_descriptor mcc ml objdetect optflow phase_unwrapping photo plot python2 python3 quality rapid reg rgbd saliency sfm shape stereo stitching structured_light superres surface_matching text tracking ts video videoio videostab xfeatures2d ximgproc xobjdetect xphoto
Disabled: world
Disabled by dependency: -
Unavailable: cnn_3dobj cvv java js julia matlab ovis viz
Applications: perf_tests examples apps
Documentation: NO
Non-free algorithms: YES
GUI:
GTK+: YES (ver 3.22.30)
GThread : YES (ver 2.56.4)
GtkGlExt: NO
OpenGL support: NO
VTK support: NO
Media I/O:
ZLib: /usr/lib/aarch64-linux-gnu/libz.so (ver 1.2.11)
JPEG: /usr/lib/aarch64-linux-gnu/libjpeg.so (ver 80)
WEBP: build (ver encoder: 0x020f)
PNG: /usr/lib/aarch64-linux-gnu/libpng.so (ver 1.6.34)
TIFF: build (ver 42 - 4.0.10)
JPEG 2000: build (ver 2.3.1)
OpenEXR: build (ver 2.3.0)
HDR: YES
SUNRASTER: YES
PXM: YES
PFM: YES
Video I/O:
DC1394: YES (2.2.5)
FFMPEG: YES
avcodec: YES (57.107.100)
avformat: YES (57.83.100)
avutil: YES (55.78.100)
swscale: YES (4.8.100)
avresample: YES (3.7.0)
GStreamer: YES (1.14.5)
v4l/v4l2: YES (linux/videodev2.h)
Parallel framework: TBB (ver 2020.2 interface 11102)
Trace: YES (with Intel ITT)
Other third-party libraries:
Lapack: NO
Eigen: YES (ver 3.3.4)
Custom HAL: YES (carotene (ver 0.0.1))
Protobuf: build (3.5.1)
NVIDIA CUDA: YES (ver 10.2, CUFFT CUBLAS FAST_MATH)
NVIDIA GPU arch: 53
NVIDIA PTX archs:
cuDNN: YES (ver 8.0.0)
OpenCL: YES (no extra features)
Include path: /home/legion/opencv/3rdparty/include/opencl/1.2
Link libraries: Dynamic load
Python 2:
Interpreter: /usr/bin/python2.7 (ver 2.7.17)
Libraries: /usr/lib/aarch64-linux-gnu/libpython2.7.so (ver 2.7.17)
numpy: /usr/lib/python2.7/dist-packages/numpy/core/include (ver 1.13.3)
install path: lib/python2.7/dist-packages/cv2/python-2.7
Python 3:
Interpreter: /usr/bin/python3 (ver 3.6.9)
Libraries: /usr/lib/aarch64-linux-gnu/libpython3.6m.so (ver 3.6.9)
numpy: /home/legion/.local/lib/python3.6/site-packages/numpy/core/include (ver 1.19.4)
install path: lib/python3.6/dist-packages/cv2/python-3.6
Python (for build): /usr/bin/python2.7
Java:
ant: NO
JNI: NO
Java wrappers: NO
Java tests: NO
Install to: /usr
-----------------------------------------------------------------
Thanks ~~

Answer 1

For points 1 and 2, you can test by passing the second argument to VideoCapture(filename[, apiPreference]). Since you have OpenCV built with ffmpeg and v4l2. I would try the following options cv::CAP_FFMPEG, and CAP_V4L2. For point 4, make sure your webcam is 1080p.