问题:

I am trying to save a simple matplotlib animation from Jake Vanderplas, but I keep getting OSError: [Errno 13] Permission denied.

I should note that I made two small modifications to Jake Vanderplas's example. I installed ffmpeg from MacPorts so I added the line plt.rcParams['animation.ffmpeg_path'] = '/opt/local/bin' and I ran into the problem discussed in (Using FFmpeg and IPython), so I added FFwriter = animation.FFMpegWriter().

Here is the code:

import numpy as np from matplotlib import pyplot as plt from matplotlib import animation plt.rcParams['animation.ffmpeg_path'] = '/opt/local/bin'  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)  FFwriter = animation.FFMpegWriter() anim.save('basic_animation.mp4', writer = FFwriter, fps=30, extra_args=['-vcodec', 'libx264'])

Here is the traceback:

File "ani_debug.py", line 34, in    anim.save('basic_animation.mp4', writer = FFwriter, fps=30, extra_args=['-vcodec', 'libx264']) File "/Users/Ben/Library/Enthought/Canopy_64bit/User/lib/python2.7/site- packages/matplotlib/animation.py", line 712, in save   with writer.saving(self._fig, filename, dpi): File "/Applications/Canopy.app/appdata/canopy-1.3.0.1715.macosx-x86_64/Canopy.app/Contents/lib/python2.7/contextlib.py", line 17, in __enter__   return self.gen.next() File "/Users/Ben/Library/Enthought/Canopy_64bit/User/lib/python2.7/site-packages/matplotlib/animation.py", line 169, in saving   self.setup(*args) File "/Users/Ben/Library/Enthought/Canopy_64bit/User/lib/python2.7/site-packages/matplotlib/animation.py", line 159, in setup   self._run() File "/Users/Ben/Library/Enthought/Canopy_64bit/User/lib/python2.7/site-packages/matplotlib/animation.py", line 186, in _run   stdin=subprocess.PIPE) File "/Applications/Canopy.app/appdata/canopy-1.3.0.1715.macosx-x86_64/Canopy.app/Contents/lib/python2.7/subprocess.py", line 709, in __init__   errread, errwrite) File "/Applications/Canopy.app/appdata/canopy-1.3.0.1715.macosx-x86_64/Canopy.app/Contents/lib/python2.7/subprocess.py", line 1326, in _execute_child   raise child_exception OSError: [Errno 13] Permission denied

I have also tried using Spyder's built-in python and received a similar traceback. Any suggestions?

EDIT: I realized that I did not give the proper path to ffmpeg. Apparently, plt.rcParams['animation.ffmpeg_path'] does not work similar to PYTHONPATH. You must tell the animation module exactly where ffmpeg is with plt.rcParams['animation.ffmpeg_path'] = '/opt/local/bin/ffmpeg'.

Now, I get a movie file that will play, but the content is completely garbled. I can't tell what I am looking at.

Here is the traceback:

Exception in Tkinter callback Traceback (most recent call last):   File "Tkinter.pyc", line 1470, in __call__   File "Tkinter.pyc", line 531, in callit   File "/Applications/Spyder.app/Contents/Resources/lib/python2.7/matplotlib/backends/backend_tkagg.py", line 141, in _on_timer     TimerBase._on_timer(self)   File "/Applications/Spyder.app/Contents/Resources/lib/python2.7/matplotlib/backend_bases.py", line 1203, in _on_timer     ret = func(*args, **kwargs)   File "/Applications/Spyder.app/Contents/Resources/lib/python2.7/matplotlib/animation.py", line 876, in _step     still_going = Animation._step(self, *args)   File "/Applications/Spyder.app/Contents/Resources/lib/python2.7/matplotlib/animation.py", line 735, in _step     self._draw_next_frame(framedata, self._blit)   File "/Applications/Spyder.app/Contents/Resources/lib/python2.7/matplotlib/animation.py", line 753, in _draw_next_frame     self._pre_draw(framedata, blit)   File "/Applications/Spyder.app/Contents/Resources/lib/python2.7/matplotlib/animation.py", line 766, in _pre_draw     self._blit_clear(self._drawn_artists, self._blit_cache)   File "/Applications/Spyder.app/Contents/Resources/lib/python2.7/matplotlib/animation.py", line 806, in _blit_clear     a.figure.canvas.restore_region(bg_cache[a]) KeyError:

EDIT: For some reason, everything is working fine now. I have tried things on my home computer and my work computer, and neither one can recreate the garbled video file I got after I fixed the ffmpeg path issue.

EDIT: Aaaahaaa! I tracked this sucker down. Sometimes I would import a module that had plt.rcParams['savefig.bbox'] = 'tight' in it. (I would never use that module, but rcParams persist, until you restart your python interpreter.) That setting causes the video to come out all garbled. I will post my solution below.

回答1:

So it turns out there were two issues.

Issue #1: The path to ffmpeg was wrong. I thought I needed to provide the path to the directory that ffmpeg resides in, but I needed to provide the path all the way to the ffmpeg binary.

Issue #2: Prior to testing out my code to generate videos, I sometimes would import a module with the setting plt.rcParams['savefig.bbox'] = 'tight'. (I did not think much of it, because I did not use the module, but rcParams persist until you restart the python interpreter.) This plt.rcParams['savefig.bbox'] = 'tight' causes the video file to save without any errors, but the frames are all garbled when you try to play the video. Although it took me all evening to track this down, it turns out this is a known issue.

Here is the updated solution that creates a video file for me with a nice, translating, sine wave.

import numpy as np from matplotlib import pyplot as plt from matplotlib import animation plt.rcParams['animation.ffmpeg_path'] = '/opt/local/bin/ffmpeg'  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)  FFwriter = animation.FFMpegWriter() anim.save('basic_animation.mp4', writer = FFwriter, fps=30, extra_args=['-vcodec', 'libx264'])

回答2:

I had garbling issues when I first (naively) tried to modify the working example of answer 3 to show the graph in realtime (as well as keep the movie).

Not quite right mods of answer 3 (which worked for me)

plt.ion() # interaction on
plt.draw() and plt.show() inside animate function, before return statent
frames=20, interval=200 to slow graph creation a bit, but still make a 4 second movie

Now plot shows up in a window as it is being created, but the output movie is garbled.

Correct step 2: