initial commit and version 1.0

moviepy/video/fx/AccelDecel.py

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+from dataclasses import dataclass
+
+from moviepy.Effect import Effect
+
+
+@dataclass
+class AccelDecel(Effect):
+    """Accelerates and decelerates a clip, useful for GIF making.
+
+    Parameters
+    ----------
+
+    new_duration : float
+      Duration for the new transformed clip. If None, will be that of the
+      current clip.
+
+    abruptness : float
+      Slope shape in the acceleration-deceleration function. It will depend
+      on the value of the parameter:
+
+      * ``-1 < abruptness < 0``: speed up, down, up.
+      * ``abruptness == 0``: no effect.
+      * ``abruptness > 0``: speed down, up, down.
+
+    soonness : float
+      For positive abruptness, determines how soon the transformation occurs.
+      Should be a positive number.
+
+    Raises
+    ------
+
+    ValueError
+      When ``sooness`` argument is lower than 0.
+
+    Examples
+    --------
+
+    The following graphs show functions generated by different combinations
+    of arguments, where the value of the slopes represents the speed of the
+    videos generated, being the linear function (in red) a combination that
+    does not produce any transformation.
+
+    .. image:: /_static/medias/accel_decel-fx-params.png
+      :alt: acced_decel FX parameters combinations
+    """
+
+    new_duration: float = None
+    abruptness: float = 1.0
+    soonness: float = 1.0
+
+    def _f_accel_decel(
+        self, t, old_duration, new_duration, abruptness=1.0, soonness=1.0
+    ):
+        a = 1.0 + abruptness
+
+        def _f(t):
+            def f1(t):
+                return (0.5) ** (1 - a) * (t**a)
+
+            def f2(t):
+                return 1 - f1(1 - t)
+
+            return (t < 0.5) * f1(t) + (t >= 0.5) * f2(t)
+
+        return old_duration * _f((t / new_duration) ** soonness)
+
+    def apply(self, clip):
+        """Apply the effect to the clip."""
+        if self.new_duration is None:
+            self.new_duration = clip.duration
+
+        if self.soonness < 0:
+            raise ValueError("'sooness' should be a positive number")
+
+        return clip.time_transform(
+            lambda t: self._f_accel_decel(
+                t=t,
+                old_duration=clip.duration,
+                new_duration=self.new_duration,
+                abruptness=self.abruptness,
+                soonness=self.soonness,
+            )
+        ).with_duration(self.new_duration)