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• 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.

• How does mp4 block matching work

  19 juin 2019, par YAHsaves

  I’ve been working on a video encoder that uses block matching to find similar blocks on previous frames.

  For the sake of simplicity I’ll leave out most of the details, but I’m wondering if I got the block matching algorithm right.

  In order to find a block on a previous frame my encoder uses the mean squared algorithm for the Y channel in YUV color space.

  This works by comparing each pixel of the block we want to match, with the block on the previous frame. It takes the difference of each pixel and squares it.

  After all the pixels are compared the block that has the least average difference is chosen as the desired block.

  Now this is where I need help. My encoder looks at every possible block in a 256x256 area and uses half pixel searches as well. The smallest block size it can use is 4x4.

  From what I’ve read online this is the same things mp4 uses.

  However I can’t find nearly as many blocks as mp4 appears to be able to find.

  For example here are 2 frames I want to compress. The first will be the I frame and the second is the P frame :

  

  Now after my encoder has run it is able to reduce the second frame by 80% and, what it can’t match close enough it saves as "difference" blocks. Which are grey blocks only recording the difference. They look like this :

  

  Now what I don’t get is to save these "difference" blocks as a jpg takes roughly 90kb to be accurate enough.

  Multiply that by 24 (24 frames per second) you get 2070kb per second. That’s not including how much space the actual motion vectors take up or anything else.

  However somehow mp4 is able to compress the video of the images above into a mere 700kb per second and still look better than my encoder at much larger data amounts.

  Why is this ? Is there something I’m doing wrong when looking for blocks ? Any help would be much appreciated.