matplotlib ArtistAnimation返回空白视频 [英] matplotlib ArtistAnimation returns a blank video

问题描述

我正在尝试制作随时间变化的networkx图的动画.我正在使用networkx_draw实用程序创建图表的matplotlib图形，并使用matplotlib的ArtistAnimation模块从networkx生成的艺术家创建动画.我对这里的操作做了最小程度的复制:

I'm trying to produce an animation of a networkx graph changing over time. I'm using the networkx_draw utilities to create matplotlib figures of the graph, and matplotlib's ArtistAnimation module to create an animation from the artists networkx produces. I've made a minimum reproduction of what I'm doing here:

import numpy as np
import networkx as nx
import matplotlib.animation as animation
import matplotlib.pyplot as plt

# Instantiate the graph model
G = nx.Graph()
G.add_edge(1, 2)

# Keep track of highest node ID
G.maxNode = 2

fig = plt.figure()
nx.draw(G)
ims = []

for timeStep in xrange(10):

    G.add_edge(G.maxNode,G.maxNode+1)
    G.maxNode += 1

    pos = nx.drawing.spring_layout(G)
    nodes = nx.drawing.draw_networkx_nodes(G, pos)
    lines = nx.drawing.draw_networkx_edges(G, pos)

    ims.append((nodes,lines,))
    plt.pause(.2)
    plt.cla()

im_ani = animation.ArtistAnimation(fig, ims, interval=200,            repeat_delay=3000,blit=True)
im_ani.save('im.mp4', metadata={'artist':'Guido'})

在实时显示人物时，该过程工作正常，它可以精确地产生我想要的动画.而且它甚至在脚本末尾的图形中生成循环动画，这也是我想要的，这表明动画处理有效.但是，当我打开保存在磁盘上的"im.mp4"文件时，它是一幅空白的白色图像，运行了预期的时间，从不显示任何实时显示的图形图像.

The process works fine while displaying the figures live, it produces exactly the animation I want. And it even produces a looping animation in a figure at the end of the script, again what I want, which would suggest that the animation process worked. However when I open the "im.mp4" file saved to disk, it is a blank white image which runs for the expected period of time, never showing any of the graph images which were showed live.

我使用的是networkx版本1.11和matplotlib版本2.0.我将ffmpeg用于动画，并在Mac OSX 10.12.3上运行.

I'm using networkx version 1.11, and matplotlib version 2.0. I'm using ffmpeg for the animation, and am running on a Mac, OSX 10.12.3.

我做错了什么?

推荐答案

简短的答案:如果您不想动画为空，请不要清除轴！ IE.删除行plt.cla().然后，您还应该删除初始的nx.draw(G)，因为它不会添加到ims数组中，否则会在动画的每一帧中停留.

The short answer: If you don't want to have an empty animation, do not clear the axes! I.e. remove the line plt.cla(). You should then also remove the initial nx.draw(G), because this is not added to the ims array and would otherwise stick around in every frame of the animation.

在此问题中可以找到原因和更详细的解释，
Matplotlib视频创建，其中也处理了类似的情况.

The reasons and a longer explanation can be found in this question,
Matplotlib video creation, where a similar case is tackled.

缺点当然是，当删除plt.cla()时，屏幕上会出现拥挤的动画.因此，您需要决定是在屏幕上绘制还是预先保存.

The drawback is of course that when removing the plt.cla() you'll end up with a crowded animation on screen; so you need to decide whether to plot on screen or whether to save beforehands.

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