title: How to apply transparency to clips in moviepy?
body: <p>So I'm trying to create a clip with moviepy where five semi-transparent clips are overlaid on each other using the CompositeVideoClip.</p>
  
  <p>The output should be a clip of length equal to the longest clip, where the all the layers of the composite clip are visible.</p>
  
  <p>My code looks something like this:</p>
  
  <pre><code>from moviepy.editor import *
  
  clip_1 = VideoFileClip('some\\path\\here.mp4')
  clip_2 = VideoFileClip('some\\path\\here.mp4')
  clip_3 = VideoFileClip('some\\path\\here.mp4')
  clip_4 = VideoFileClip('some\\path\\here.mp4')
  clip_5 = VideoFileClip('some\\path\\here.mp4')
  
  list_of_clips = [clip_1, clip_2, clip_3, clip_4, clip_5]
  
  for index, clip in enumerate(list_of_clips):
      list_of_clips[index] = clip.set_opacity(.20)
  
  output_clip = CompositeVideoClip(list_of_clips)
  
  output_clip.write_videofile('some\\path\\here.mp4')
  </code></pre>
  
  <p>Code runs fine, except transparency is not applied.</p>
  
  <p>Neither does this work:</p>
  
  <pre><code>clip = VideoFileClip(some\\path\\here.mp4).set_opacity(.30)
  
  clip.write_videofile(some\\path\\here.mp4)
  </code></pre>
  
  <p>Export works fine, but clip is fully opaque.</p>
  
  <p>Any suggestions for how to achieve transparency in clip outputs?</p>