title: Matplotlib ArtistAnimation showing multiple elements in one step
body: <p>I've been using matplotlib for a while to create plots but have just now discovered the <code>animation</code> options. I want to show a series of plots (not just individual elements) in an animation using <code>animation.ArtistAnimation</code>.</p>
  
  <p>Unfortunately, I can't get it to animate multiple plotted elements at a time. Here's a minimal example to explain what I mean:</p>
  
  <pre class="lang-py prettyprint-override"><code>import random
  import matplotlib.pyplot as plt
  import matplotlib.animation as animation
  
  fig = plt.figure()
  
  ims = []
  for _ in range(10):
      im1, = plt.plot([random.randrange(10), random.randrange(10)], [random.randrange(10), random.randrange(10)])
      im2, = plt.plot([random.randrange(10), random.randrange(10)], [random.randrange(10), random.randrange(10)])
      ims.append((im1,))
      ims.append((im2,))
  ani = animation.ArtistAnimation(fig, ims)
  
  ani.save('im.mp4')
  </code></pre>
  
  <p>This randomly generates two lines <code>im1</code>, <code>im2</code> 10x. I always want to see both <code>im1</code> and <code>im2</code> at the same time. But this only shows one line at a time.
  If I comment <code>ims.append((im1,))</code>, the background is full of static lines, but it still just animates one line.
  I also tried to combine <code>im1</code> and <code>im2</code> using <code>im1 + im2</code> or <code>[im1, im2]</code>, but both lead to errors.</p>
  
  <p>Extra question: Is there any reason why <code>blit=False</code> by default? I thought, it's supposed to improve performance?</p>