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• OpenCV 4.5.2 takes a long time (>100ms) to retrieve a single frame from a webcam, C++ on Windows 10

  9 juin 2021, par Mustard Tiger

  I've been having a tough time getting my webcam working quickly with opencv. Frames take a very long time to read, (a recorded average of 124ms across 500 frames) I've tried on three different computers (running Windows 10) with a logitech C922 webcam. The most recent machine I tested on has a Ryzen 9 3950X, with 32gbs of ram ; no lack of power.

  


  Here is the code :

  


  cv::VideoCapture cap = cv::VideoCapture(m_cameraNum);&#xA;&#xA;// Check if camera opened successfully&#xA;if (!cap.isOpened())&#xA;{&#xA;    m_logger->critical("Error opening video stream or file\n\r");&#xA;    return -1;&#xA;}&#xA;&#xA;bool result = true;&#xA;result &amp;= cap.set(cv::CAP_PROP_FRAME_WIDTH, 1280);&#xA;result &amp;= cap.set(cv::CAP_PROP_FRAME_HEIGHT, 720);&#xA;&#xA;bool ready = false;&#xA;std::vector<string> timeLog;&#xA;timeLog.reserve(50000);&#xA;int i = 0;&#xA;&#xA;while (i &lt; 500)&#xA;{&#xA;    auto start = std::chrono::system_clock::now();&#xA;    &#xA;    cv::Mat img;&#xA;    ready = cap.read(img);&#xA;&#xA;    // If the frame is empty, break immediately&#xA;    if (!ready)&#xA;    {&#xA;        timeLog.push_back("continue");&#xA;        continue;&#xA;    }&#xA;&#xA;    i&#x2B;&#x2B;;&#xA;    auto end = std::chrono::system_clock::now();&#xA;    timeLog.push_back(std::to_string(std::chrono::duration_cast(end - start).count()));&#xA;}&#xA;&#xA;for (auto&amp; entry : timeLog)&#xA;    m_logger->info(entry);&#xA;&#xA;cap.release();&#xA;return 0;&#xA;</string>

  


  Notice that I write the elapsed time to a log file at the end of execution. The average time is 124ms for debug and release, and not one instance of "continue" after half a dozen runs.

  


  It doesn't matter if I use USB 2 or USB 3 ports (the camera is USB2) or if I run a debug build or a release build, the log file will show anywhere from 110ms to 130ms of time for each frame. The camera works fine in other app, OBS can get a smooth 1080@30fps or 720@60fps.

  


  Stepping through the debugger and doing a lot of Googling, I've learned the following about my system :

  


  

  • The backend chosen by default is DSHOW. GStreamer and FFMPEG are also available.

  


  • DSHOW uses FFMPEG somehow (it needs the FFMPEG dll) but I cannot use FFMPEG directly through opencv. Attempting to use cv::VideoCapture(m_cameraNum, cv::CAP_FFMPEG) always fails. It seems like Opencv's interface to FFMPEG is only capable of opening video files.

  


  • Microsoft really screwed up camera devices in Windows a few years back, not sure if this is related to my problem.

  


  


  Here's a short list of the fixes I have tried, most taken from older SO posts :

  


  

  • result &= cap.set(cv::CAP_PROP_FRAME_COUNT, 30) ; // Returns false, does nothing

  


  • result &= cap.set(cv::CAP_PROP_CONVERT_RGB, 0) ; // Returns true, does nothing

  


  • result &= cap.set(cv::CAP_PROP_MODE, cv::VideoWriter::fourcc('M', 'J', 'P', 'G')) ; // Returns false, does nothing

  


  • Set registry key from http://alax.info/blog/1693 that should disable the new Windows camera server.

  


  • Updated from 4.5.0 to 4.5.2, no change.

  


  • Asked device manager to find a newer driver, no newer driver found.

  


  


  I'm out of ideas. Any help ?

  


• sh : /usr/bin/ffmpeg : not found

  22 janvier 2016, par Rio

  I’m trying to execute ffmpeg from PHP using shell_exec or exec but it fails. Why can this be ? The command /usr/bin/ffmpeg works from the terminal, so I tried

  <?php
  
  $cmd = "/usr/bin/ffmpeg";
  
  exec($cmd." 2>&1", $out, $ret);
  
  if ($ret){
  
      echo "There was a problem!\n";
  
      print_r($out);
  
  }else{
  
      echo "Everything went better than expected!\n";
  
  }
  
  ?>

  and I keep on getting

  There was a problem! Array ( [0] => sh: /usr/bin/ffmpeg: not found )

  Any help would be greatly appreciated.

  Permission on the executable are

  -rwxr-xr-x  1 root   root      106552 Jun 12 09:53 ffmpeg

  Running which /usr/local/bin/ffmpeg into $cmd returns an empty Array.

• python3 openCV VideoCapture only black image (Raspbian Stretch)

  21 juin 2018, par PrimuS

  I have a little python function that analyzes a video, chunks it into one image per second and gives me the most dominant color for that image. (Code can be found here : https://github.com/primus852/python-movie-barcode)

  This works great on my Windows testing environment. However, on my Rasbian Stretch Raspberry Pi Setup it only produces a black image, as the source seems to be black.

  I compiled OpenCV (3.4.1) myself with this great article : https://www.pyimagesearch.com/2017/09/04/raspbian-stretch-install-opencv-3-python-on-your-raspberry-pi/, and it worked perfectly fine. I am using python3 and a virtualenv.

  I tried adding the ffmpeg package : apt install ffmpeg, to no avail.

  2 ideas

  • I compiled the openCV source without support for mkv/mp4/similar ? If so, how would I check that and can I just "re-compile" the whole package ?
  • I am missing codecs, where would I be able to check that ?

  The crucial code (I think) is this :

  cap = cv2.VideoCapture(full_path) are there other options that do not break the majority of my code ? I read about skvideo.io from scikit-video but that does not seem to work with my code...

  I am new to python, any hint is appreciated

  // EDIT, I think it is not a duplicate because I pass the I get no error that the capture cannot be opened and :

  OpenCV FFMPEG support :

  • python -c "import cv2; print(cv2.getBuildInformation())" | grep -i ffmpeg
    • returns : FFMPEG: YES

  FFMPEG Codec :

  • ffmpeg -codecs | grep -i avc (file is using AVC)
    • returns : DEV.LS h264 H.264 / AVC / MPEG-4 AVC / MPEG-4 part 10 (decoders: h264 h264_mmal h264_vdpau ) (encoders: libx264 libx264rgb h264_omx h264_vaapi )

  File PATH

  It exists and the path is correct...

  Any other ideas ? Could it possibly the virtualenv ?

  //EDIT2

  Tried with an AVI file

  works...