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• 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 ...

• Streaming Video from RTMP to EMGUCV

  22 juillet 2017, par Isuru

  I’m trying to stream a webcam using RTMP to an EMGUCV project in order to process the video. I have set up a private RTMP server in a linux box using this tutorial,
  https://obsproject.com/forum/resources/how-to-set-up-your-own-private-rtmp-server-using-nginx.50/

  I’m testing the webcam stream using ffmpeg with the following commands,

  • Write to the rtmp server using,

    ffmpeg -y -f vfwcap -framerate 25 -video_size 640x480 -i 0 -an -f flv rtmp://rtmp-server:1935/live/stream

  • Read from the rtmp server using,
    ffplay -fflags nobuffer rtmp ://rtmp-server:1935/live/stream -loglevel verbose

  I’m able to write a simple OpenCV C++ application to read the stream and display it. Code below,

      cv::VideoCapture vcap;
  
      cv::Mat image;
  
      const std::string videoStreamAddress = "rtmp://rtmp-server:1935/live/stream";
  
      if(!vcap.open(videoStreamAddress)) {
  
          printf("Error opening video stream or file");
  
          return -1;
  
      }
  
  
  
      cv::namedWindow("Output Window");
  
      cv::Mat edges;
  
      for(;;) {
  
          if(!vcap.read(image)) {
  
              printf("No frame");
  
              cv::waitKey();
  
          }
  
          cv::imshow("Output Window", image);
  
          if(cv::waitKey(1) >= 0) break;
  
      }
  
  return 0;

  The above code works properly. However when I try it using EMGUCV C#, I get the error message
  unable to create to capture from rtmp://rtmp-server:1935/live/stream

  This is my C# Code,

      public partial class MainForm : Form
  
      {
  
          private static Capture _cameraCapture;
  
  
  
          public MainForm()
  
          {
  
              InitializeComponent();
  
              Run();
  
          }
  
  
  
          void Run()
  
          {
  
              try
  
              {
  
                  _cameraCapture = new Capture("rtmp://192.168.56.101:1935/live/stream");                
  
              }
  
              catch (Exception e)
  
              {
  
                  MessageBox.Show(e.Message);
  
                  return;
  
              }            
  
          }
  
     }

  Do I need a specific build of EMGUCV with FFMPEG or is RTMP capturing not available in EMGUCV ?

• Evolution #2173 (Résolu) : Date de création / publication

  13 janvier 2018, par nico d_

  J’ai ajouté la doc du plugin : https://contrib.spip.net/ecrire/?exec=article&id_article=4967

  Pas encore publiée, mais je propose de fermer ce ticket dès qu’elle le sera, et de continuer la discussion sur le forum du plugin sur contrib.