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• OpenCV videocapture() not opening video file from hard disk

  8 janvier 2020, par Rossi Riccardo

  Despite being a lot of threads on the issue of open CV not being able to open videos i still can’t manage to solve it.

  I’m trying to open and extract frames using openCV with spyder (os : windows 10, python 3.7.4). As far as i know (provided the file path is correct) cv2.read returns a 0 if either the codec is unsupported (converted the video to H264 to be sure and also downloaded a test avi used to test out this very issue in an older post ) or if there is a problem with the ffmpeg dependency.

  Since i thought this was the source of the issue i added conda and phyton to the PATH with the SETX command and, after that, ended up copying ffmpeg dll and cv2 folders everywhere since i couldn’t understand well were i was supposed to paste it. Results is that i still can’t make it work and can’t even opt to try to make the frame extractor directly with ffmpeg since even that one gives me an error with a copypasted function from it’s site.

  Here is the code :

  import os 
  
  import ffmpeg
  
  
  
  
  
  def read_frame_as_jpeg(in_filename, frame_num):
  
      out, err = (
  
          ffmpeg
  
          .input(in_filename)
  
          .filter('select', 'gte(n,{})'.format(frame_num))
  
          .output('pipe:', vframes=1, format='image2', vcodec='mjpeg')
  
          .run(capture_stdout=True)
  
      )
  
  
  
  # Read the video from specified path 
  
  #cam = cv2.VideoCapture(r'C:\MY\folder\264H.mp4') 
  
  cam = cv2.VideoCapture(r'C:\Users\name\Downloads\drop.avi') 
  
  fps=60
  
  vid_start=371
  
  vid_end=377
  
  sens=20
  
  out_dir=r"C:\MY\folder"
  
  out_dir=out_dir+'\\'
  
  print(out_dir)
  
  
  
  stri="drop.avi"#even tried putting the fiel in the same directory, no change
  
  read_frame_as_jpeg(stri, 1)
  
  
  
  # frame 
  
  currentframe = 0
  
  
  
  while(True): 
  
  
  
      # reading from frame 
  
      ret,frame = cam.read()
  
  
  
      print(currentframe)
  
      if ret and currentframe>= (fps*vid_start)-sens and currentframe<= (fps*vid_end)+sens: 
  
          # if video is still left continue creating images 
  
          name = out_dir+ str(currentframe) + '.bmp'
  
          print ('Creating...' + name) 
  
  
  
          # writing the extracted images 
  
          cv2.imwrite(name, frame) 
  
  
  
          # increasing counter so that it will 
  
          # show how many frames are created 
  
          currentframe += 1
  
      else: 
  
          break
  
  
  
  # Release all space and windows once done 
  
  cam.release() 
  
  cv2.destroyAllWindows()  

  The ffpeg error that i get is

  [WinError 2] Impossible to find the specified file

  while on the other hand since videocapture returns a 0 it doesn’t even enter the loop so i get just a "0" print

• Reading JPEG in ffmpeg

  16 juillet 2021, par Paul Lammertsma

  I'm trying to get ffmpeg to encode several individual JPEG images into a video on Android. I've successfully built it for Android (see the configuration string at the end of this post).

  



  I can encode an h.263+ video with randomly generated frame content, and ffmpeg otherwise appears to work well.

  



  A similar question suggests that the following code should be sufficient to load an image into an AvFrame :

  



  // Make sure we have the codecs
av_register_all();

AVFormatContext *pFormatCtx;
int ret = av_open_input_file(&pFormatCtx, imageFileName, NULL, 0, NULL);

if (ret != 0) {
    printf("Can't open image file '%s': code %d, %s",
        imageFileName, ret, strerror(AVERROR(ret)));
}


  



  The above returns the correct absolute file path and error :

  



  


  Failed '/sdcard/DCIM/Camera/IMG083.jpg' : code -1094995529, Unknown error : 1094995529

  


  



  Incidentally, if I omit av_register_all(), it returns with error 2.

  



  I've compiled ffmpeg with the following arguments :

  



  


  


  ./configure —target-os=linux 
 —prefix=$PREFIX 
 —enable-cross-compile 
 —extra-libs="-lgcc" 
 —arch=arm 
 —cc=$PREBUILT/bin/arm-linux-androideabi-gcc 
 —cross-prefix=$PREBUILT/bin/arm-linux-androideabi- 
 —nm=$PREBUILT/bin/arm-linux-androideabi-nm 
 —sysroot=$PLATFORM 
 —extra-cflags=" -O3 -fpic -DANDROID -DHAVE_SYS_UIO_H=1 -Dipv6mr_interface=ipv6mr_ifindex -fasm -Wno-psabi -fno-short-enums -fno-strict-aliasing -finline-limit=300 $OPTIMIZE_CFLAGS " 
 —enable-shared 
 —enable-static 
 —extra-ldflags="-Wl,-rpath-link=$PLATFORM/usr/lib -L$PLATFORM/usr/lib -nostdlib -lc -lm -ldl -llog" 
 —disable-everything 
 —enable-demuxer=mov 
 —enable-demuxer=h264 
 —disable-ffplay 
 —enable-protocol=file 
 —enable-avformat 
 —enable-avcodec 
 —enable-decoder=mjpeg 
 —enable-decoder=png 
 —enable-parser=h264 
 —enable-encoder=h263 
 —enable-encoder=h263p 
 —disable-network 
 —enable-zlib 
 —disable-avfilter 
 —disable-avdevice

  


  


  



  Any suggestions would be most welcome !

  


• Reading JPEG in ffmpeg

  23 octobre 2012, par Paul Lammertsma

  I'm trying to get ffmpeg to encode several individual JPEG images into a video on Android. I've successfully built it for Android (see the configuration string at the end of this post).

  I can encode an h.263+ video with randomly generated frame content, and ffmpeg otherwise appears to work well.

  A similar question suggests that the following code should be sufficient to load an image into an AvFrame :

  // Make sure we have the codecs
  
  av_register_all();
  
  
  
  AVFormatContext *pFormatCtx;
  
  int ret = av_open_input_file(&pFormatCtx, imageFileName, NULL, 0, NULL);
  
  
  
  if (ret != 0) {
  
      printf("Can't open image file '%s': code %d, %s",
  
          imageFileName, ret, strerror(AVERROR(ret)));
  
  }

  The above returns the correct absolute file path and error :

  Failed '/sdcard/DCIM/Camera/IMG083.jpg' : code -1094995529, Unknown error : 1094995529

  Incidentally, if I omit av_register_all(), it returns with error 2.

  I've compiled ffmpeg with the following arguments :

  ./configure —target-os=linux
  —prefix=$PREFIX
  —enable-cross-compile
  —extra-libs="-lgcc"
  —arch=arm
  —cc=$PREBUILT/bin/arm-linux-androideabi-gcc
  —cross-prefix=$PREBUILT/bin/arm-linux-androideabi-
  —nm=$PREBUILT/bin/arm-linux-androideabi-nm
  —sysroot=$PLATFORM
  —extra-cflags=" -O3 -fpic -DANDROID -DHAVE_SYS_UIO_H=1 -Dipv6mr_interface=ipv6mr_ifindex -fasm -Wno-psabi -fno-short-enums -fno-strict-aliasing -finline-limit=300 $OPTIMIZE_CFLAGS "
  —enable-shared
  —enable-static
  —extra-ldflags="-Wl,-rpath-link=$PLATFORM/usr/lib -L$PLATFORM/usr/lib -nostdlib -lc -lm -ldl -llog"
  —disable-everything
  —enable-demuxer=mov
  —enable-demuxer=h264
  —disable-ffplay
  —enable-protocol=file
  —enable-avformat
  —enable-avcodec
  —enable-decoder=mjpeg
  —enable-decoder=png
  —enable-parser=h264
  —enable-encoder=h263
  —enable-encoder=h263p
  —disable-network
  —enable-zlib
  —disable-avfilter
  —disable-avdevice

  Any suggestions would be most welcome !