helpers/music_effect.py

   1 class GainEffect:
   2     effect_types = [
   3         'fade'
   4     ]
   5
   6     def __init__(self, effect, audio_segment, initial_loop, start, end,
   7             **kwargs):
   8         if effect in self.effect_types:
   9             self.effect = effect
  10         else:
  11             raise Exception("Unknown effect {}".format(effect))
  12
  13         self.start = start
  14         self.end = end
  15         self.audio_segment = audio_segment
  16         self.initial_loop = initial_loop
  17         getattr(self, self.effect + "_init")(**kwargs)
  18
  19     def get_last_gain(self):
  20         return getattr(self, self.effect + "_get_last_gain")()
  21
  22     def get_next_gain(self, current_frame, current_loop, frame_count):
  23         # This returns two values:
  24         # - The first one is the gain to apply on that frame
  25         # - The last one is True or False depending on whether it is the last
  26         #   call to the function and the last gain should be saved permanently
  27         return getattr(self, self.effect + "_get_next_gain")(
  28                 current_frame,
  29                 current_loop,
  30                 frame_count)
  31
  32     # Fading
  33     def fade_init(self, gain=0, **kwargs):
  34         self.audio_segment_frame_count = self.audio_segment.frame_count()
  35         self.first_frame = int(
  36                 self.audio_segment_frame_count * self.initial_loop +\
  37                 self.audio_segment.frame_rate * self.start)
  38         self.last_frame = int(
  39                 self.audio_segment_frame_count * self.initial_loop +\
  40                 self.audio_segment.frame_rate * self.end)
  41         self.gain= gain
  42
  43     def fade_get_last_gain(self):
  44         return self.gain
  45
  46     def fade_get_next_gain(self, current_frame, current_loop, frame_count):
  47         current_frame = current_frame \
  48                 + (current_loop - self.initial_loop) \
  49                     * self.audio_segment_frame_count
  50
  51         if current_frame >= self.last_frame:
  52             return [self.gain, True]
  53         elif current_frame < self.first_frame:
  54             return [0, False]
  55         else:
  56             return [
  57                     (current_frame - self.first_frame) / \
  58                             (self.last_frame - self.first_frame) * self.gain,
  59                     False
  60                     ]
  61
  62