Can't save matplotlib animation

问题:

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

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?

回答1:

You need to specify your path to ffmpeg:

On linux I use:

import numpy as np
from matplotlib import pyplot as plt
from matplotlib import animation
plt.rcParams['animation.ffmpeg_path'] = '/usr/bin/ffmpeg'

You will obviously have to point to your windows .exe instead of '/usr/bin/ffmpeg'

If you don't have ffmpeg installed, you can get it here

回答2:

for some animation "anim" i use on windows:

plt.rcParams['animation.ffmpeg_path'] ='E:\\Media\\ffmpeg\\bin\\ffmpeg.exe'
FFwriter = animation.FFMpegWriter()
anim.save('basic_animation.mp4', writer = FFwriter, fps=30)

where path should be with \ \ and not with / or \ between folders

回答3:

Line 183 in animation.py is the subprocess.Popen call to ffmpeg. It seems that the ffmpeg exe is not where matplotlib expects it to be.

My first attempt would be to put the install path (directory) to ffmpeg into the windows Path environmental variable. I'm guessing that animation.py is expecting it to be available globally (as it would be under Linux).

If that doesn't work, I'd inspect the subprocess.Popen call in animation.py to see exactly what it is doing. You could break point it or adjust the verbose.report variable in your matplotlibrc file to spit it out. Line 179 there is:

verbose.report('MovieWriter.run: running command: %s' %
                   ' '.join(command))

回答4:

On Windows, I had to use plt.rcParams['animation.ffmpeg_path'] = 'C:\\mypath' with all double '\' in the path and this line has to be mentioned before

from matplotlib import animation

and mypath = path of ffmpeg.exe on the local disk.

Additionally, I also added the ffmpeg path in the environment variables.

It took me two days and after going through tons of advice I was able to solve this issue of saving animation.

Thank you everyone for all the answers.