title: OpenCV VideoCapture() doesn't work - Ubuntu
body: <p>OpenCV 4.5  -  Ubuntu  -  Jetson Nano 2GB</p>
  <p>Hello I have a problem with getting video from my webcam (connected by USB to JetsonNano) by OpenCV</p>
  <p>Here's my code:</p>
  <pre><code> // cv::VideoCapture cap( ... );
      cv::Mat frame;
      if (!cap.isOpened())  // if not success, exit program
      {
          cout &lt;&lt; &quot;Cannot open the video cam&quot; &lt;&lt; endl;
          return -1;
      }
      cv::namedWindow(&quot;test&quot;, cv::WINDOW_AUTOSIZE);
      while(true)
      {
          try
          {
              cap &gt;&gt; frame;
              cv::imshow(&quot;test&quot;, frame);
          }
          catch(const std::exception&amp; e)
          {
              std::cerr &lt;&lt; e.what() &lt;&lt; '\n';
          }
      }
  </code></pre>
  <p>1 | <code>cv::VideoCapture cap(0)</code> gives me:</p>
  <pre><code>[ 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
  </code></pre>
  <p>2 | <code>cv::VideoCapture cap(&quot;/dev/video0&quot;)</code> gives me:</p>
  <pre><code>[ 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
  </code></pre>
  <p>3 | When I try to open camera by command, only this one work:
  <code>$ gst-launch-1.0 v4l2src device=\&quot;/dev/video0\&quot; ! xvimagesink</code>
  I gave it a try:
  <code>cv::VideoCapture cap(&quot;v4l2src device=\&quot;/dev/video0\&quot; ! xvimagesink&quot;)</code> it gives me:</p>
  <pre><code>[ 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
  </code></pre>
  <p>If I gave other sinks : autosink or appsink, it's also doesn't work.</p>
  <p>4 | I tried the solution from that link
  <a href="https://forums.developer.nvidia.com/t/sony-camera-module-cannot-be-opened-with-opencv-on-xavier/84003" rel="nofollow noreferrer">https://forums.developer.nvidia.com/t/sony-camera-module-cannot-be-opened-with-opencv-on-xavier/84003</a></p>
  <p><code>cv::VideoCapture cap(&quot;v4l2src device=/dev/video0 ! video/x-raw,width=1920,height=1080,format=UYVY,framerate=30/1 ! videoconvert ! video/x-raw,format=BGR ! appsink&quot;)</code> and it's gives me :</p>
  <pre><code>[ 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'
  </code></pre>
  <p><strong>Someone knows what's going on and how to fix it?</strong></p>
  <p>Edit#1:
  My OpenCV buildinfo :</p>
  <pre><code>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
  -----------------------------------------------------------------
  </code></pre>
  <p>Thanks ~~</p>