Call resize on mask when newsize is a function of time (#1200)

CHANGELOG.md

@@ -55,7 +55,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - `AudioFileClip` would not generate audio identical to the original file [#1108]
 - Several issues resulting from incorrect time values due to floating point errors [#1195], for example:
     - Blank frames at the end of clips [#210]
-    - Sometimes getting `IndexError: list index out of range` when using `concatenate_videoclips` [#646] 
+    - Sometimes getting `IndexError: list index out of range` when using `concatenate_videoclips` [#646]
+- Applying `resize` with a non-constant `newsize` to a clip with a mask would remove the mask [#1200] 
 
 
 ## [v1.0.3](https://github.com/zulko/moviepy/tree/v1.0.3) (2020-05-07)

moviepy/video/fx/resize.py

@@ -98,6 +98,7 @@ def trans_newsize(ns):
                 return ns
 
         if hasattr(newsize, "__call__"):
+            # The resizing is a function of time
 
             def newsize2(t):
                 return trans_newsize(newsize(t))
@@ -114,12 +115,15 @@ def fun(gf, t):
                 def fun(gf, t):
                     return resizer(gf(t).astype("uint8"), newsize2(t))
 
-            return clip.fl(
+            newclip = clip.fl(
                 fun, keep_duration=True, apply_to=(["mask"] if apply_to_mask else [])
             )
+            if apply_to_mask and clip.mask is not None:
+                newclip.mask = resize(clip.mask, newsize, apply_to_mask=False)
 
-        else:
+            return newclip
 
+        else:
             newsize = trans_newsize(newsize)
 
     elif height is not None:
@@ -132,7 +136,6 @@ def fun(t):
             return resize(clip, fun)
 
         else:
-
             newsize = [w * height / h, height]
 
     elif width is not None:
@@ -144,7 +147,8 @@ def fun(t):
 
             return resize(clip, fun)
 
-        newsize = [width, h * width / w]
+        else:
+            newsize = [width, h * width / w]
 
     # From here, the resizing is constant (not a function of time), size=newsize