Fix audio normalizing for mute clips (Zulko#1401)

CHANGELOG.md

@@ -27,6 +27,7 @@ Lots of method and parameter names have been changed. This will be explained bet
 - Fixed `rotate` sometimes failing with `ValueError: axes don't match array` [\#1335](https://github.com/Zulko/moviepy/pull/1335)
 - Fixed positioning error generating frames in `CompositeVideoClip` [\#1420](https://github.com/Zulko/moviepy/pull/1420)
 - Changed deprecated `tostring` method by `tobytes` in `video.io.gif_writers::write_gif` [\#1429](https://github.com/Zulko/moviepy/pull/1429)
+- Fixed calling `audio_normalize` on a clip with no sound causing `ZeroDivisionError` [\#1401](https://github.com/Zulko/moviepy/pull/1401)
 
 
 ## [v2.0.0.dev2](https://github.com/zulko/moviepy/tree/v2.0.0.dev2) (2020-10-05)

moviepy/audio/fx/audio_normalize.py

@@ -19,4 +19,9 @@ def audio_normalize(clip):
     """
 
     max_volume = clip.max_volume()
-    return volumex(clip, 1 / max_volume)
+    if max_volume == 0:
+        # Nothing to normalize.
+        # Avoids a divide by zero error.
+        return clip.copy()
+    else:
+        return volumex(clip, 1 / max_volume)

tests/test_fx.py

@@ -1,7 +1,9 @@
 import os
 
+import numpy as np
 import pytest
 
+from moviepy.audio.AudioClip import AudioClip
 from moviepy.audio.fx.audio_normalize import audio_normalize
 from moviepy.audio.io.AudioFileClip import AudioFileClip
 from moviepy.utils import close_all_clips
@@ -456,5 +458,14 @@ def test_normalize():
     close_all_clips(locals())
 
 
+def test_normalize_muted():
+    z_array = np.array([0.0])
+    make_frame = lambda t: z_array
+    clip = AudioClip(make_frame, duration=1, fps=44100)
+    clip = audio_normalize(clip)
+    assert np.array_equal(clip.to_soundarray(), z_array)
+    close_all_clips(locals())
+
+
 if __name__ == "__main__":
     pytest.main()