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• cv2.VideoCapture() taking extremely long time to connect and returning empty frames

  18 novembre 2022, par John Schmidt

  When executing the code

  


  cap = cv2.VideoCapture('udp://127.0.0.1:1080',cv2.CAP_FFMPEG)


  


  The script will yield for at least a minute, and then connect. Along with that, it seems that, almost at random, the script will completely break and cv2.VideoCapture() will return nothing. the stream is initiated with the command

  


  ffmpeg.exe -y -f dshow -thread_queue_size 4096 -hwaccel cuda -hwaccel_output_format cuda -i video="OBS Virtual Camera" -f rawvideo -c:v mjpeg -qscale:v 0 -r 20 udp://127.0.0.1:1080


  


  if that helps any.

  


  I tried many different methods of starting the stream, color formats, and more. Still, they all had this issue.

  


  (note this does work sometimes, but seemingly at random will completely stop working for many days to come, and then suddenly begin working)

  


• Accord.Video.FFMPEG getting error for long video

  30 novembre 2022, par wahyu

  I use Accord.Video.FFMPEG to extract images every 10 frames from a video. Total frames for this video is 38194 frames. First run is good, I can save image every 10 frames but after run of about 38185 frames i got null return from this code Bitmap bmpBaseOriginal = vReader.ReadVideoFrame();, if I see in the video there is no problem at the end of video.

  


  I do something like this

  


  using (var vReader = new VideoFileReader())
{
    vReader.Open(files[0]);
    TotalFrame = vReader.FrameCount;
    countin = Convert.ToInt32(TotalFrame / Convert.ToDouble(countAsset));
    Fps = vReader.FrameRate.Value;                                
    int a = 0;
    for (int i = 0; i < vReader.FrameCount; i++)
    {
         if(i < vReader.FrameCount - 1)
         {
              Bitmap bmpBaseOriginal = vReader.ReadVideoFrame();
              if (i%10 == 0)
              {
                  a++;
                  bmpBaseOriginal.Save(string.Format("{0}\\{1}.jpeg", dirVideo.FullName, a), ImageFormat.Jpeg);
              }
              bmpBaseOriginal.Dispose();
         }
         else
         {
              a++;
              Bitmap bmpBaseOriginal = vReader.ReadVideoFrame();
              bmpBaseOriginal.Save(string.Format("{0}\\{1}.jpeg", dirVideo.FullName, a), ImageFormat.Jpeg);
              bmpBaseOriginal.Dispose();
         }
    }
    vReader.Close();
}


  


  this problem occurs again on another video if the video has a lot of frames, but no problem if the video has a less frames.

  


  How to solve it ?

  


• opencv-python initial rtmp stream(cv2.VideoCapture(rtmp_url)), it takes a long time

  2 décembre 2022, par yang bai

  Question

  


  

  1. When read the stream from camera or video(with '-re' arg), the opencv initial will takes a long time about 10-30s.

  


  2. And the latency is about 2-3s, any optimzation suggestion ?

  


  


  Enviroment

  


  os : ubuntu 18.04

  


  rtmp serve : nginx + nginx-rtmp-module (default configuration)

  


  stream source : use camera

  


  Code

  


  push code :

  


  cap = cv2.VideoCapture(0)
fps = int(cap.get(cv2.CAP_PROP_FPS))
width = int(cap.get(cv2.CAP_PROP_WIDTH))
height = int(cap.get(cv2.CAP_PROP_HEIGHT))

rtmp_url = 'xxxx'

command = ['ffmpeg',
           '-re',
           '-y',
           '-flags', 'low_delay',
           '-f', 'rawvideo',
           '-vcodec', 'rawvideo',
           '-pix_fmt', 'bgr24',
           '-s', ''.format(width, height),
           '-r', str(fps),
           '-i', '-',
           '-c:v', 'libx264',
           '-pix_fmt', 'yuv420p',
           '-preset', 'ultrfast',
           '-f', 'flv',
           rtmp_url]

p = sp.Popen(command, stdin=sp.PIPE)
while cap.isOpened():
  ret, frame = cap.read()
  if ret:
    p.stdin.write(frame.tostring())
  else:
    break


  


  read code

  


  cap = cv2.VideoCapture(rtmp_url) # this code line will takes long time
...


  


  try to change the nginx conf 'chunk_size', but make no difference.

  


  and try to push in Windows : ffmpeg -f dshow -i video="Integrated Webcam" -s 640*480 -r 15 -vcodec libx264 -preset:v ultrafast -tune:v zerolatency -acodec libfaac -f flv rtmp://192.168.0.199:1935 rtmp_url again, no effect. only reduce a little latency.