def f_accel_decel(t, old_d, new_d, abruptness=1, soonness=1.0):
"""
abruptness
negative abruptness (>-1): speed up down up
zero abruptness : no effect
positive abruptness: speed down up down
soonness
for positive abruptness, determines how soon the
speedup occurs (0<soonness < inf)
"""
a = 1.0+abruptness
def _f(t):
f1 = lambda t: (0.5)**(1-a)*(t**a)
f2 = lambda t: (1-f1(1-t))
return (t<.5)*f1(t) + (t>=.5)*f2(t)
return old_d*_f((t/new_d)**soonness)
[docs]def accel_decel(clip, new_duration=None, abruptness=1.0, soonness=1.0):
"""
new_duration
If None, will be that of the current clip.
abruptness
negative abruptness (>-1): speed up down up
zero abruptness : no effect
positive abruptness: speed down up down
soonness
for positive abruptness, determines how soon the
speedup occurs (0<soonness < inf)
"""
if new_duration is None:
new_duration = clip.duration
fl = lambda t : f_accel_decel(t, clip.duration, new_duration,
abruptness, soonness)
return clip.fl_time(fl).set_duration(new_duration)