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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

• subprocess ffmpeg multiple drawtext

  6 juillet 2012, par knishua

  stuck here, how is it possible to pass multiple parameters in ffmpeg via subprocess

  1. this command works in 'cmd'

     ffmpeg -threads 8 -i D :/imagesequence/background.jpg -vf "movie='D~:/imagesequence/thumbnail.jpg' [watermark] ; [in][watermark] overlay=(main_w-overlay_w)/2 :(main_h-overlay_h)/3[water] ;[water] drawtext=fontsize=32:fontcolor=White:fontfile=/Windows/Fonts/arial.ttf:text='shotName':x=(w)/2:y=(h)-50,drawtext=fontsize=28:fontcolor=White:fontfile=/Windows/Fonts/arial.ttf:text='Notes ~:':x=(w)/5:y=(h)-90,drawtext=fontsize=28:fontcolor=White:fontfile=/Windows/Fonts/arial.ttf:text='Frame Range ~:':x=(w)/5:y=(h)-130,drawtext=fontsize=28:fontcolor=White:fontfile=/Windows/Fonts/arial.ttf:text='Lens ~:':x=(w)/5:y=(h)-170,drawtext=fontsize=28:fontcolor=White:fontfile=/Windows/Fonts/arial.ttf:text='Undistortion ~:':x=(w)/5:y=(h)-210,drawtext=fontsize=28:fontcolor=White:fontfile=/Windows/Fonts/arial.ttf:text='Image Sequence ~:':x=(w)/5:y=(h)-250,drawtext=fontsize=28:fontcolor=White:fontfile=/Windows/Fonts/arial.ttf:text='Date ~:':x=(w)/5:y=(h)-290,drawtext=fontsize=28:fontcolor=White:fontfile=/Windows/Fonts/arial.ttf:text='Element Name ~:':x=(w)/5:y=(h)-330,drawtext=fontfile=/Windows/Fonts/arial.ttf:text='FUTUREWORKS':x=130:y=200:fontsize=54:fontcolor=White[out]" D :\imagesequence\dpx\brn_055.0000.dpx

  2. when trying thru subprocess it fails. instead of trying the whole of it, tried

     thj = "D~:/imagesequence/thumbnail.jpg"
     paramd = "movie='%s'[watermark] ;[in][watermark]overlay=(main_w-overlay_w)/2 :(main_h-overlay_h)/3[water] ;[water]drawtext=fontsize=32:fontcolor=White:fontfile=/Windows/Fonts/arial.ttf:text=\'shotName\':x=(w)/2:y=(h)-50[out]" % thj
     subprocess.check_call(["ffmpeg", "-threads", "8", "-i", "D :/imagesequence/background.jpg", "-vf", paramd ,"D :/imagesequence/dpx/brn_055.0000.dpx"], shell=True)

  This is only putting 1 text instead of 5 text on the screen

  any different view on this. how to successfully run this command

• what live streaming formats supports gud quality video call from speeding car(80kmph)

  13 juin 2013, par neckTwi

  video call drops when i'm in my car at more than 50kmph. i'm using ffmpeg to out-stream my video and vlc to capture friend's in-stream in flv rtmp live stream format on ubuntu with airtel 3g usb data card(3Mbps).

  what is the best streaming format and ffmpeg video quality options in this case ? are there any modems(with antennas) that support this system ?