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• How to create a named pipe in Windows ?

  10 février 2023, par Che

  Is it possible without much effort (e.g. in command line or powershell), to create a named pipe ?

  


  My goal is to write continously to that pipe from a ffmpeg-process.

  


  Without opening a Pipe at first the following command

  


  ffmpeg -i "path\to\my\File\name of my File" -f webm \\.\pipe\from_ffmpeg


  


  fails to

  


  


  "\.\pipe\from_ffmpeg : No such file or directory"

  


  


  In the big picture, I want to read a Live-Web-Video-Stream to analyze it and take live-actions based on that.
I am working with OpenCV in Java on a Windows machine. At the moment I have different ffmpeg-processes, which record different sectors (i.e. pixels (45, 45, 100, 100) and (200, 200, 100, 100) (x, y, height, width). The results are saved as jpg files in the filesystem and are then opened in a Java Process. This works, but I think I would significantly gain performance by not taking the long way over the files but to directly pipe my input into the Java-Process.

  


  I know there's an option to live-capture videostreams via open-CV but the framework does not support as many formats as ffmpeg does.

  


• Different filesizes for images generated using octave and python

  22 février 2017, par Lakshay Garg

  I am using python (scikit-image) and octave to generate 200 images as follows

  Python3

  import numpy as np
  
  from skimage.io import imsave
  
  
  
  images = [255*np.ones((100,100), dtype=np.uint8),  # white
  
               np.zeros((100,100), dtype=np.uint8)]  # black
  
  
  
  for i in range(200): # save alternating black and white images
  
      imsave('%04d.png'%(i+1), images[i%2])

  Octave

  pkg load image;
  
  
  
  im1 = 255*ones(100,100); # white
  
  im2 = zeros(100,100);    # black
  
  for i=1:200
  
      name = sprintf('%04d.png', i);
  
      if mod(i,2) == 0
  
          imwrite(im1, name);
  
      else
  
          imwrite(im2, name);
  
      end
  
  end

  Next, I use ffmpeg to generate two videos (alternating white and black frames) from these two sets of images using the following command

  ffmpeg -r 10 -loglevel quiet \
  
         -i ./%04d.png -c:v libx264 \
  
         -preset ultrafast -crf 0 ./out.mkv

  1. Sizes of image files generated by both these codes are different.

     • Octave white : 192 bytes, black : 98 bytes
     • Python white : 120 bytes, black : 90 bytes

  2. Sizes of video files generated from these octave and python images are significantly different from each other.

     • Octave filesize : 60 kilobytes
     • Python filesize : 116 kilobytes

  Why do we have this apparently very strange behavior ?

  EDIT

  Since it was suggested that the behavior might be dues to octave and python using different bit-depths to store the images, I changes the octave code to use 8 bit numbers

  im1 = uint8(255*ones(100,100)); # white
  
  im2 = uint8(zeros(100,100));    # black

  and now the image file sizes are nearly the same

  • Octave white : 118 bytes, black : 90 bytes
  • Python white : 120 bytes, black : 90 bytes

  but the problem is still the same for video files, octave : 60K, python : 116K

• FFmpeg : Is it better to make a application then using ffmepg directly

  14 juillet 2020, par Mirabeau

  For all my IP camera streams, I use, under Linux, ffmpeg by a bash script which allows me at the same time to manage :

  


  1/ Convert the RTSP streams to HTTP (HLS) for the "Live" and therefore which generates "m3u8" file and *.ts segments

  


  2/ Backup the stream for archiving (in increments of 5 minutes), a cron remove older files (xx days)

  


  ffmpeg -i "rtsp://[IP_CAM01]" -rtsp_transport tcp -c copy -map 0 -f segment -segment_time 300 -segment_atclocktime 1 -segment_format mkv "cam01-% 03d.mkv" -c copy -f segment -segment_list cam01.m3u8 -segment_list_flags + live -segment_time 2 -segment_list_size 20 -segment_wrap 20 cam01-% 03d.ts


  


  The question I ask myself, and the reason for this message is as follows :

  


  

  • would there be an interest (memory / cpu / speed) to develop a program (C/C++/other ?) to do the same thing by using the libraries of ffmpeg ?

  


  • or the "gain" and the interest would be so minimal that it is not worth the expenditure of energy and time ?

  


  


  I appeal to your feedback, your opinions, your tips !, and if you had leads (sample) to attack this kind of development, I am interested.

  


  Thank you very much in advance for your feedback.
(this is my fist question on stackoverflow, Champagne ! ;))