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• Although ffmpeg installed, unable to save mp4 file on disk

  2 janvier 2020, par yannis

  Although I have installed ffmpeg, matplotlib reports that MovieWriter ffmpeg is unavailable and the MP4 file created is empty.

  import numpy as np
  
  from matplotlib import pyplot as plt
  
  from matplotlib import animation
  
  
  
  # First set up the figure, the axis, and the plot element we want to animate
  
  fig = plt.figure()
  
  ax = plt.axes(xlim=(0, 2), ylim=(-2, 2))
  
  line, = ax.plot([], [], lw=2)
  
  
  
  # initialization function: plot the background of each frame
  
  def init():
  
      line.set_data([], [])
  
      return line,
  
  
  
  # animation function.  This is called sequentially
  
  def animate(i):
  
      x = np.linspace(0, 2, 1000)
  
      y = np.sin(2 * np.pi * (x - 0.01 * i))
  
      line.set_data(x, y)
  
      return line,
  
  
  
  # call the animator.  blit=True means only re-draw the parts that have changed.
  
  anim = animation.FuncAnimation(fig, animate, init_func=init,
  
                                 frames=200, interval=20, blit=True)
  
  
  
  # save the animation as an mp4.  This requires ffmpeg or mencoder to be
  
  # installed.  The extra_args ensure that the x264 codec is used, so that
  
  # the video can be embedded in html5.  You may need to adjust this for
  
  # your system: for more information, see
  
  # http://matplotlib.sourceforge.net/api/animation_api.html
  
  anim.save('basic_animation.mp4', fps=30, extra_args=['-vcodec', 'libx264'])
  
  
  
  plt.show()

  I have even added the line plt.switch_backend('TkAgg') proposed in another post, nothing changed. Here is my matplotlib :

  Name: matplotlib
  
  Version: 2.1.0
  
  Summary: Python plotting package
  
  Home-page: http://matplotlib.org

  my ffmpeg :

  Name: ffmpeg
  
  Version: 1.4
  
  Summary: ffmpeg python package url [https://github.com/jiashaokun/ffmpeg]
  
  Home-page: https://github.com/jiashaokun/ffmpeg

  and my Python version :

  Python 3.6.5

  The error I get is :

  /usr/local/lib/python3.6/site-packages/matplotlib/animation.py:1218: UserWarning: MovieWriter ffmpeg unavailable
  
    warnings.warn("MovieWriter %s unavailable" % writer)

  This error has been reported many times on stackoverflow, each time the solution is either to install ffmpeg (mine is installed) or to add that extra line about the backend, which hasn’t changed anything for me.

  Curiously enough the plt.show()command works and I do preview an animation, but the only file format to save it is (nonanimated) PNG.

• ffmpeg map and filter_complex subprocess in python

  4 décembre 2015, par jlarsch

  I want to crop and re encode videos via ffmpeg from within python using subprocesses.

  I managed starting a subprocess using a pure string command and shell=True but I want to build more complex commands and would prefer to use shell=False and passing a list of arguments.

  So what works is this form (this is a simplified example, there will be multiple streams in the final version) :

  import subprocess as sp
  
  
  
  sp.Popen('ffmpeg.exe -i Test.avi -filter_complex "[0:v]crop=1024:1024:0:0[out1]" -map [out1] out1.mp4', shell=True)

  This script produces the expected cropped output video.

  For a list of arguments, I tried :

  FFMPEG_PATH = 'ffmpeg.exe'
  
  aviP='Test.avi'
  
  sp.Popen([FFMPEG_PATH,
  
  '-i', aviP,
  
  '-filter_complex', '[0:v]crop=1024:1024:0:0[out1]',
  
  '-map', '[out1] out1.mp4'])

  When I execute this second version, simply nothing happens. (no error, no output)

  I suspect I am messing up something in the map command syntax ?

• Ffmpeg map and filter_complex subprocess - Python

  4 décembre 2015, par jlarsch

  I want to crop and re encode videos via ffmpeg from within python using subprocesses.

  I managed starting a subprocess using a pure string command and shell=True but I want to build more complex commands and would prefer to use shell=False and passing a list of arguments.

  So what works is this form (this is a simplified example, there will be multiple streams in the final version) :

  import subprocess as sp
  
  
  
  sp.Popen('ffmpeg.exe -i Test.avi -filter_complex "[0:v]crop=1024:1024:0:0[out1]" -map [out1] out1.mp4', shell=True)

  This script produces the expected cropped output video.

  For a list of arguments, I tried :

  FFMPEG_PATH = 'ffmpeg.exe'
  
  aviP='Test.avi'
  
  sp.Popen([FFMPEG_PATH,
  
  '-i', aviP,
  
  '-filter_complex', '[0:v]crop=1024:1024:0:0[out1]',
  
  '-map', '[out1] out1.mp4'])

  When I execute this second version, simply nothing happens. (no error, no output)

  I suspect I am messing up something in the map command syntax ?