Fix fundamental floating point error in Clip.iter_frames (#1195)

CHANGELOG.md

@@ -53,6 +53,9 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - `IndexError` in `vfx.freeze`, `vfx.time_mirror` and `vfx.time_symmetrize` [#1124]
 - Using `rotate()` with a `ColorClip` no longer crashes [#1139]
 - `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] 
 
 
 ## [v1.0.3](https://github.com/zulko/moviepy/tree/v1.0.3) (2020-05-07)

moviepy/Clip.py

@@ -466,7 +466,11 @@ def iter_frames(self, fps=None, with_times=False, logger=None, dtype=None):
                      for frame in myclip.iter_frames()])
         """
         logger = proglog.default_bar_logger(logger)
-        for t in logger.iter_bar(t=np.arange(0, self.duration, 1.0 / fps)):
+        for frame_index in logger.iter_bar(t=np.arange(0, int(self.duration * fps))):
+            # int is used to ensure that floating point errors are rounded
+            # down to the nearest integer
+            t = frame_index / fps
+
             frame = self.get_frame(t)
             if (dtype is not None) and (frame.dtype != dtype):
                 frame = frame.astype(dtype)

tests/test_compositing.py

@@ -38,3 +38,26 @@ def test_clips_array_duration():
     video = clips_array([[red, green, blue]]).set_duration(5)
     video.write_videofile(join(TMP_DIR, "test_clips_array.mp4"))
     close_all_clips(locals())
+
+
+def test_concatenate_self():
+    clip = BitmapClip([["AAA", "BBB"], ["CCC", "DDD"]]).set_fps(1)
+    target = BitmapClip([["AAA", "BBB"], ["CCC", "DDD"]]).set_fps(1)
+
+    concatenated = concatenate_videoclips([clip])
+
+    concatenated.write_videofile(join(TMP_DIR, "test_concatenate_self.mp4"))
+    assert concatenated == target
+
+
+def test_concatenate_floating_point():
+    """
+    >>> print("{0:.20f}".format(1.12))
+    1.12000000000000010658
+
+    This test uses duration=1.12 to check that it still works when the clip duration is
+    represented as being bigger than it actually is. Fixed in #1195.
+    """
+    clip = ColorClip([100, 50], color=[255, 128, 64], duration=1.12).set_fps(25.0)
+    concat = concatenate_videoclips([clip])
+    concat.write_videofile("concat.mp4", preset="ultrafast")