无法使用 openccv 打开视频文件

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2. >>> vc = cv2.VideoCapture('test.mp4')
   
3. Failed to query video capabilities: Inappropriate ioctl for device
   
4. libv4l2: error getting capabilities: Inappropriate ioctl for device
   
5. VIDEOIO ERROR: V4L: device test.mp4: Unable to query number of channels
   
6. OpenCV(3.4.1) Error: Unspecified error (GStreamer: your gstreamer installation is missing a required plugin
   
7. ) in handlemessage, file /builddir/build/BUILD/opencv-3.4.1/modules/videoio/src/cap_gstreamer.cpp, line 1869
   
8. VIDEOIO(cvCreateCapture_GStreamer (CV_CAP_GSTREAMER_FILE, filename)): raised OpenCV exception:
   
9. 
   
10. OpenCV(3.4.1) /builddir/build/BUILD/opencv-3.4.1/modules/videoio/src/cap_gstreamer.cpp:1869: error: (-2) GStreamer: your gstreamer installation is missing a required plugin
    
11. in function handlemessage
    

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同样情况，opencv是通过dnf安装的：

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2. dnf install python3-opencv
   

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