[Python] Moviepy - Output video not playable

I'm using the library moviepy on Linux Mint 18.1.

Specifically, it's moviepy 0.2.3.2 on python 3.5.2

Since I'm getting started, I tried this simple script, which should concatenate two videos one after the other:

import moviepy.editor as mp

video1 = mp.VideoFileClip("short.mp4")
video2 = mp.VideoFileClip("motivation.mp4")

final_video = mp.concatenate_videoclips([video1,video2])
final_video.write_videofile("composition.mp4")


The two videos are short random videos that I downloaded from YouTube. They both play perfectly, both with VLC and the standard video player provided with Linux Mint.

The script runs fine with no errors, with the final message:

[MoviePy] >>>> Building video composition.mp4
[MoviePy] Writing audio in compositionTEMP_MPY_wvf_snd.mp3
100%|██████████████████████████████| 1449/1449 [00:23<00:00, 59.19it/s]
[MoviePy] Done.
[MoviePy] Writing video composition.mp4
100%|██████████████████████████████| 1971/1971 [11:34<00:00, 2.84it/s]
[MoviePy] Done.
[MoviePy] >>>> Video ready: composition.mp4


The file is indeed created, and it also have a size (about 20 MB). However, when I try to play it, nothing happens: it seems to be corrupted. The standard video player even tells me that "there is no video stream to be played".

If I try to do the same with the interactive console, and use final_video.preview(), I get an AttributeError, along with this traceback:

In [5]: final_video.preview()
Exception in thread Thread-417:
Traceback (most recent call last):
File "/usr/lib/python3.5/threading.py", line 914, in _bootstrap_inner
self.run()
File "/usr/lib/python3.5/threading.py", line 862, in run
self._target(*self._args, **self._kwargs)
File "<decorator-gen-211>", line 2, in preview
File "/usr/local/lib/python3.5/dist-packages/moviepy/decorators.py", line 54, in requires_duration
return f(clip, *a, **k)
File "/usr/local/lib/python3.5/dist-packages/moviepy/audio/io/preview.py", line 49, in preview
sndarray = clip.to_soundarray(tt,nbytes=nbytes, quantize=True)
File "<decorator-gen-184>", line 2, in to_soundarray
File "/usr/local/lib/python3.5/dist-packages/moviepy/decorators.py", line 54, in requires_duration
return f(clip, *a, **k)
File "/usr/local/lib/python3.5/dist-packages/moviepy/audio/AudioClip.py", line 107, in to_soundarray
fps = self.fps
AttributeError: 'CompositeAudioClip' object has no attribute 'fps'


and the video seems frozen at the first frame.

I don't have any clue, since everything seems to work fine (except with the preview, which doesn't work because of the error). I tried to reinstall ffmpeg, but no succes: everything is exactly the same. Without any useful error, how can I fix this problem?

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