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• Can't save matplotlib animation

  19 novembre 2014, par renger

  I am trying to get a simple animation saved using ffmpeg. I followed a tutorial to install ffmpeg, and I can now access it from the command prompt.

  Now I run this piece of code :

  import numpy as np
  
  from matplotlib import pyplot as plt
  
  from matplotlib import animation
  
  
  
  fig = plt.figure()
  
  ax = plt.axes(xlim=(0, 2), ylim=(-2, 2))
  
  line, = ax.plot([], [], lw=2)
  
  
  
  def init():
  
      line.set_data([], [])
  
      return line,
  
  
  
  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,
  
  
  
  anim = animation.FuncAnimation(fig, animate, init_func=init,
  
                                 frames=200, interval=20, blit=True)
  
  
  
  mywriter = animation.FFMpegWriter()
  
  anim.save('mymovie.mp4',writer=mywriter)
  
  
  
  plt.show()

  I get this error :

  Traceback (most recent call last):
  
    File "<stdin>", line 1, in <module>
  
     File "C:\Python27\lib\site-packages\spyderlib\widgets\externalshell\sitecustomize.py", line 523, in runfile
  
      execfile(filename, namespace)
  
    File "C:\Users\Renger\.xy\startups\b.py", line 23, in <module>
  
      anim.save('mymovie.mp4',writer=mywriter)
  
    File "C:\Python27\lib\site-packages\matplotlib\animation.py", line 609, in save
  
      with writer.saving(self._fig, filename, dpi):
  
    File "C:\Python27\lib\contextlib.py", line 17, in __enter__
  
      return self.gen.next()
  
    File "C:\Python27\lib\site-packages\matplotlib\animation.py", line 166, in saving
  
      self.setup(*args)
  
    File "C:\Python27\lib\site-packages\matplotlib\animation.py", line 156, in setup
  
      self._run()
  
    File "C:\Python27\lib\site-packages\matplotlib\animation.py", line 183, in _run
  
      stdin=subprocess.PIPE)
  
    File "C:\Python27\lib\subprocess.py", line 711, in __init__
  
      errread, errwrite)
  
    File "C:\Python27\lib\subprocess.py", line 948, in _execute_child
  
      startupinfo)
  
  WindowsError: [Error 2] Het systeem kan het opgegeven bestand niet vinden
  
  </module></module></stdin>

  The last dutch sentence does mean something like : The system can’t find the specified file.

  What do these errors mean, and how can I solve them ?

• Revision b1b4ba1bdd : Properly save neon registers. Replace current code which corrupts the stack by

  27 septembre 2013, par Christian Duvivier

  Changed Paths :
   Modify /vp9/common/arm/neon/vp9_idct16x16_neon.c

  
   Add /vp9/common/arm/neon/vp9_save_reg_neon.asm

  
   Modify /vp9/common/arm/neon/vp9_short_idct16x16_add_neon.asm

  
   Modify /vp9/vp9_common.mk

  
  
  Properly save neon registers.

  Replace current code which corrupts the stack by
  duplicate of vp8 code to save and restore neon
  registers.

  Change-Id : Ibb0220b9aa985d10533befa0a455ebce57a2891a

• FFMPEG : how to save input camera stream into the file with the SAME codec format ?

  19 janvier 2014, par user3211926

  I have the camera-like device that produces video stream and passes it into my Windows-based machine via USB port.

  Using the command :

  ffmpeg -y -f vfwcap -i list

  I see that (as expected) FFmpeg finds the input stream as stream #0.

  Using the command :

  ffmpeg -y -f vfwcap -r 25 -i 0 c:\out.mp4

  I can successfully save the input stream into the file.

  From the log I see :

  Stream #0:0 : Video : rawvideo (UYVY / 0x59565955), uyvy422, 240x320, 25 tbr, 1k tbn, 25 tbc
  No pixel format specified, yuv422p for H.264 encoding chosen.

  So, my input format is transcoded to yuv422p.

  My question :

  • How can I cause FFmpeg to save my input video stream into out.mp4 WITHOUT transcoding - actually, to copy input stream to output file as close as possible, with the same format ?