title: ValueError: MoviePy couldn't find the codec associated with the filename. Provide the 'codec' parameter in write_videofile
body: <p>Why is it throwing this error on some files, and for other files it doesn't ?</p>
  
  <p>The files are all .mp4 videos.</p>
  
  <blockquote>
    <p>'ValueError: MoviePy couldn't find the codec associated with the filename. Provide the 'codec' parameter in write_videofile.'</p>
  </blockquote>
  
  <h1>The code, with comments:</h1>
  
  <pre><code>    # The videos on which we will work on (intro &amp; a video)
      intro = VideoFileClip('./videos/intro.mp4')
      original = VideoFileClip('./videos/original_video.mp4')
  
  
      # We cut 2s and crop the original video
      original.cutout(0, 2)
      original = vfx.crop(original, x1=10)
  
  
      # Adding a watermark on top of the original video
      watermark = (ImageClip("./images/watermark.png")
                      .set_duration(original.duration)
                      .set_position(("center","bottom"))
                      .resize(width=intro.w))
      watermaked = CompositeVideoClip([original, watermark], size=original.size)
  
  
      # Our final video: Intro + Waterkarmed, and output it.
      final_render = concatenate_videoclips([intro, watermaked], method='compose')
      final_render.write_videofile('./videos/output_video.mp4', fps=30, threads=1)
  </code></pre>
  
  <h1>The error stack:</h1>
  
  <pre><code>  final_render.write_videofile('./videos/output_video.mp4', fps=30, threads=1)
  
    File "&lt;decorator-gen-51&gt;", line 2, in write_videofile
    File "/usr/lib/python2.7/site-packages/moviepy/decorators.py", line 54, in requires_duration
      return f(clip, *a, **k)
    File "&lt;decorator-gen-50&gt;", line 2, in write_videofile
    File "/usr/lib/python2.7/site-packages/moviepy/decorators.py", line 137, in use_clip_fps_by_default
      return f(clip, *new_a, **new_kw)
    File "&lt;decorator-gen-49&gt;", line 2, in write_videofile
    File "/usr/lib/python2.7/site-packages/moviepy/decorators.py", line 22, in convert_masks_to_RGB
      return f(clip, *a, **k)
    File "/usr/lib/python2.7/site-packages/moviepy/video/VideoClip.py", line 288, in write_videofile
      raise ValueError("MoviePy couldn't find the codec associated "
  ValueError: MoviePy couldn't find the codec associated with the filename. Provide the 'codec' parameter in write_videofile.
  </code></pre>