'Returns a Clip instance playing the content of the current clip
but with a modified timeline, time ``t`` being replaced by another
time `t_func(t)`.
Parameters
t_func:
A function ``t-> new_t``
apply_to:
Can be either \'mask\', or \'audio\', or [\'mask\',\'audio\'].
Specifies if the filter ``fl`` should also be applied to the
audio or the mask of the clip, if any.
keep_duration:
``False`` (default) if the transformation modifies the
``duration`` of the clip.
Examples
>>> # plays the clip (and its mask and sound) twice faster
>>> newclip = clip.fl_time(lambda: 2*t, apply_to=[\'mask\',\'audio\'])
>>> # plays the clip starting at t=3, and backwards:
>>> newclip = clip.fl_time(lambda: 3-t)'

def fl_time(self, t_func, apply_to=None, keep_duration=False):

    if (apply_to is None):
        apply_to = []
    return self.fl((lambda gf, t: gf(t_func(t))), apply_to, keep_duration=keep_duration)
