问尽管安装了mp4，但无法在磁盘上保存ffmpeg文件

EN

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()

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

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

Python 3.6.5

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