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• OpenCV 4.5.2 VideoWriter produces “can't find starting number” error

  28 avril 2021, par Peter Kronenberg

  There are several issues with similar names, but none of them seem to have a definitive answer. Using the last version of OpenCV 4.5.2 with Java on Windows 10. Below is a short reproducible test case which results in

  


  [ERROR:0] global C:\build\master_winpack-bindings-win64-vc14-static\opencv\modules\videoio\src\cap.cpp (589) cv::VideoWriter::open VIDEOIO(CV_IMAGES): raised OpenCV exception:

OpenCV(4.5.2) C:\build\master_winpack-bindings-win64-vc14-static\opencv\modules\videoio\src\cap_images.cpp:253: error: (-5:Bad argument) CAP_IMAGES: can't find starting number (in the name of file): C:/testfiles/output.avi in function 'cv::icvExtractPattern'


  


  Here is the code :

  


  public class OpenCVError {

    public static void main(String[] args) {
        System.loadLibrary(Core.NATIVE_LIBRARY_NAME);

        final int fourcc = VideoWriter.fourcc('m', 'j', 'p', 'g');
        final double fps = 30.00;
        Size frameSize = new Size(1080, 1920);
        VideoWriter videoWriter = new VideoWriter("C:/testfiles/output.avi", fourcc, fps, frameSize, true);
    }
}


  


  Update

  


  Found out from https://forum.opencv.org/t/error-in-java-cant-find-starting-number-in-the-name-of-file/3014 that I seem to be missing opencv_videoio_ffmpeg452_64.dll
I am using the Maven distribution at

  


    <dependency>&#xA;            <groupid>org.openpnp</groupid>&#xA;            <artifactid>opencv</artifactid>&#xA;            <version>4.5.1-2</version>&#xA;  </dependency>&#xA;

  


  which doesn't appear to have this file. I tried adding the file to my classpath (using IntelliJ), but it still doesn't seem to work.

  


  Anyone have any ideas ? Why isn't this file part of the openpnp distribution ?

  


• How to fetch video frame and its timestamp from ffmpeg to python code

  14 février 2017, par vijiboy

  Searching for an alternative as OpenCV would not provide timestamps which were required in my computer vision algorithm, I found this excellent article https://zulko.github.io/blog/2013/09/27/read-and-write-video-frames-in-python-using-ffmpeg/
  Working up the code on windows I still could’nt get the frame timestamps.
  I recollected seeing on ffmpeg forum somewhere that the video filters like showinfo are bypassed when redirected.

  Here’s what I tried :

  import subprocess as sp
  
  import numpy
  
  import cv2
  
  
  
  command = [ 'ffmpeg', 
  
              '-i', 'e:\sample.wmv',
  
              '-pix_fmt', 'rgb24',
  
              '-vcodec', 'rawvideo',
  
              '-vf', 'showinfo', # video filter - showinfo will provide frame timestamps
  
              '-an','-sn', #-an, -sn disables audio and sub-title processing respectively
  
              '-f', 'image2pipe', '-'] # we need to output to a pipe
  
  
  
  pipe = sp.Popen(command, stdout = sp.PIPE, stderr = sp.STDOUT) # TODO someone on ffmpeg forum said video filters (e.g. showinfo) are bypassed when stdout is redirected to pipes??? 
  
  
  
  for i in range(10):
  
      raw_image = pipe.stdout.read(1280*720*3)
  
      img_info = pipe.stdout.read(244) # 244 characters is the current output of showinfo video filter
  
      print "showinfo output", img_info
  
      image1 =  numpy.fromstring(raw_image, dtype='uint8')
  
      image2 = image1.reshape((720,1280,3))  
  
  
  
      # write video frame to file just to verify
  
      videoFrameName = 'Video_Frame{0}.png'.format(i)
  
      cv2.imwrite(videoFrameName,image2)
  
  
  
      # throw away the data in the pipe's buffer.
  
      pipe.stdout.flush()

  So how to still get the frame timestamps from ffmpeg into python code so that it can be used in my computer vision algorithm ...

• Anomalie #2787 (Nouveau) : Bug d’interprétation d’une liste suivie de paragraphes

  6 juillet 2012, par nicolas -

  En entrée dans un formulaire de forum : Faisons un test. - Premier item de liste. - Deuxième item de liste. - Troisième item de liste. Un paragraphe. Un autre. Encore un autre. En sortie : Faisons un test. Premier item de liste. Deuxième item de liste. Troisième item de liste. Un paragraphe. Un (...)