`sage -pip install --user ffmpeg` did not make the "`OSError: Error: ffmpeg does not appear to be installed.`" message go away

Question

我是 运行 Docker Cocalc 在 Ubuntu 16 服务器上的一个实例。一切似乎都在工作，但我正在尝试调试为什么 sage -pip install --user ffmpeg 没有使“OSError: Error: ffmpeg does not appear to be installed.”消息消失，即使它说它已安装。这是完整的消息。

Error in lines 9-9
Traceback (most recent call last):
  File "/usr/local/sage/local/lib/python2.7/site-packages/smc_sagews/sage_server.py", line 1188, in execute
    flags=compile_flags) in namespace, locals
  File "", line 1, in <module>
  File "/usr/local/sage/local/lib/python2.7/site-packages/smc_sagews/sage_salvus.py", line 2944, in show
    s = show0(objs, combine_all=True)
  File "/usr/local/sage/local/lib/python2.7/site-packages/smc_sagews/sage_salvus.py", line 2903, in show0
    b = show0(a)
  File "/usr/local/sage/local/lib/python2.7/site-packages/smc_sagews/sage_salvus.py", line 2868, in show0
    show_animation(obj, **kwds)
  File "/usr/local/sage/local/lib/python2.7/site-packages/smc_sagews/sage_salvus.py", line 2642, in show_animation
    obj.ffmpeg(t, delay=delay, **kwds)
  File "/usr/local/sage/local/lib/python2.7/site-packages/sage/plot/animate.py", line 885, in ffmpeg
    raise OSError(msg)
OSError: Error: ffmpeg does not appear to be installed. Saving an animation to
a movie file in any format other than GIF requires this software, so
please install it and try again.

作为参考，这里是给出错误的代码：

n = var("n")
frames = []
xr = (x, 0, 1)
for k in srange(1, 50):
    g = plot((sum((-1)^(n-1)*sin(n*x)/n,n,1,k)), xr, color="blue", legend_label='k = %d' % k)
    g += plot(x/2, xr, color="green", legend_label="x/2")
    frames.append(g)

a = animate(frames, ymin=0.0, ymax=1.0, legend_loc=(0.2,0.8))
a.show()

Answer 1

尝试在系统范围内安装 ffmpeg 软件包？

sudo docker exec -it <name of cocalc container> bash
apt-get install ffmpeg # or something like that