FFmpeg errors are not being caught when using BitmapClip

[tburrows13]

This is a strange one, because test_VideoFileClip.test_write_frame_errors() (from #1164) still behaves as expected, but BitmapClip acts differently. I'll get round to investigating it myself at some point if no one else does.

Expected Behavior

.write_videofile() fails when given an incorrect codec.

Actual Behavior

It says that it has succeeded, but no file is actually created:

Moviepy - Building video bitmap.avi.
Moviepy - Writing video bitmap.avi
Moviepy - Done !
Moviepy - video ready bitmap.avi

Steps to Reproduce the Problem

from moviepy.editor import *
c = BitmapClip([["R"], ["G"], ["B"], ["O"], ["W"]]).set_fps(1)
c.write_videofile("bitmap.avi", codec="avrn")

When I manually inspect proc.stderr, it says Unknown encoder 'avrn', but this is not raising an IOError so the error is never raised:

moviepy/moviepy/video/io/ffmpeg_writer.py

Line 136 in 5c7a69e

except IOError as err:

Specifications

• Python Version: 3.7
• Moviepy Version: Latest 2.0.0 branch
• Platform Name: macOS
• Platform Version: 10.15.5 Catalina