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• 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 command : stream generated raw video over RTSP

  21 juillet 2022, par Jan Discart

  I'm looking into using FFmpeg for streaming an output generated by an application to another system in the same network. However, I find the list of commands a little daunting and hard to understand. So I hope I can ask your help in the matter.

  



  My current usecase :
I have a Unity application which has a separate output stream of video and using a plugin I'm able to save that output to a videofile. The command used is to save this to file is :

  



  ffmpeg -y -f rawvideo -vcodec rawvideo -pixel_format rgba -colorspace bt709 -video_size 1280x720 -framerate 30 -loglevel warning -i - -pix_fmt yuv444p -preset ultrafast -crf 0 test.mp4


  



  The output format and such are already correct, but I'd like to stream this output directly over a network now, preferably using RTSP. Using the command below, where I replaced the test.mp4 at the end with udp://127.0.0.1:23000 to test streaming over UDP, but this returns an IOException in Unity.

  



  Any help in guiding me in the right direction is greatly appreciated.
Thanks in advance !

  


• libzvbi-teletextdec : propagate errors generated in page handler

  25 octobre 2013, par Marton Balint

  libzvbi-teletextdec : propagate errors generated in page handler
  Signed-off-by : Marton Balint <cus@passwd.hu>
  

  • [DH] libavcodec/libzvbi-teletextdec.c