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• Piping to FFMPEG with Python subprocess freezes

  23 septembre 2023, par Simon Streicher

  With the following code, I am able to pipe frames of a video to FFMPEG using Python, Numpy and the FFMPEG binaries :

  



  from __future__ import print_function
import subprocess
import numpy as np
import sys

npshape = [480, 480]
cmd_out = ['ffmpeg',
           '-y', # (optional) overwrite output file if it exists
           '-f', 'rawvideo',
           '-vcodec','rawvideo',
           '-s', '%dx%d'%(npshape[1], npshape[0]), # size of one frame
           '-pix_fmt', 'rgb24',
           '-r', '24', # frames per second
           '-i', '-', # The input comes from a pipe
           '-an', # Tells FFMPEG not to expect any audio
           '-vcodec', 'mpeg4',
           'output.mp4']

fout = subprocess.Popen(cmd_out, stdin=subprocess.PIPE, stderr=subprocess.PIPE).stdin

for i in range(24*40):
    if i%(24)==0: 
        print('%d'%(i/24), end=' ')
        sys.stdout.flush()

    fout.write((np.random.random(npshape[0]*npshape[1]*3)*128).astype('uint8').tostring())

fout.close()


  



  This works fine if I write anything less than 37 seconds worth of frames, but if I try to write anything more, the code just hangs. What is the underlying cause for this behaviour ? How can I fix it ?

  


• Piping to FFMPEG with Python subprocess freezes

  5 décembre 2016, par Simon Streicher

  With the following code, I am able to pipe frames of a video to FFMPEG using Python, Numpy and the FFMPEG binaries :

  from __future__ import print_function
  
  import subprocess
  
  import numpy as np
  
  import sys
  
  
  
  npshape = [480, 480]
  
  cmd_out = ['ffmpeg',
  
             '-y', # (optional) overwrite output file if it exists
  
             '-f', 'rawvideo',
  
             '-vcodec','rawvideo',
  
             '-s', '%dx%d'%(npshape[1], npshape[0]), # size of one frame
  
             '-pix_fmt', 'rgb24',
  
             '-r', '24', # frames per second
  
             '-i', '-', # The input comes from a pipe
  
             '-an', # Tells FFMPEG not to expect any audio
  
             '-vcodec', 'mpeg4',
  
             'output.mp4']
  
  
  
  fout = subprocess.Popen(cmd_out, stdin=subprocess.PIPE, stderr=subprocess.PIPE).stdin
  
  
  
  for i in range(24*40):
  
      if i%(24)==0: 
  
          print('%d'%(i/24), end=' ')
  
          sys.stdout.flush()
  
  
  
      fout.write((np.random.random(npshape[0]*npshape[1]*3)*128).astype('uint8').tostring())
  
  
  
  fout.close()

  This works fine if I write anything less than 37 seconds worth of frames, but if I try to write anything more, the code just hangs. What is the underlying cause for this behaviour ? How can I fix it ?

• How do i use libavfilter to deinterlace frames in my video player software

  19 juin 2014, par justanothercoder

  I’m using libavformat/libavcodec/libswscale/libavutil/libavfilter (ffmpeg related libraries) to make a video player.

  I’v gotten into issues with interlaced videos, it just pairs them incorrectly... It always draws the previous bottom frame with the current top frame. Which results in things I don’t want. And i’v tried messing about with the variables around this, it just won’t work. (I haven’t found a player which would play the videos I have correctly, no you can’t have them, i’m sorry)

  I managed to find a way around this, by re-encoding the video with the following command :

  ffmpeg -i video.mp4 -filter:v yadif -vcodec mpeg4 out.avi

  Now what i’d need is directions on how to do this with c++ code, inside my video player.

  I haven’t found any tutorials on the matter and the ffmpeg.c source code is just too alien to me.

  A link to a tutorial would be fine, i just haven’t found it..

  Edit :

  Also this example was worth checking out :

  https://github.com/krieger-od/imgs2video/blob/master/imgs2video.c

  It’s by a gentleman named Andrey Utkin