Add fading

1 files changed, 50 insertions, 0 deletions

diff --git a/helpers/music_effect.py b/helpers/music_effect.py
new file mode 100644
index 0000000..ef8dc90
--- /dev/null
+++ b/helpers/music_effect.py
@@ -0,0 +1,50 @@
+class GainEffect:
+    effect_types = [
+        'fade'
+    ]
+
+    def __init__(self, effect, audio_segment, start, end, **kwargs):
+        if effect in self.effect_types:
+            self.effect = effect
+        else:
+            raise Exception("Unknown effect {}".format(effect))
+
+        self.start = start
+        self.end = end
+        self.audio_segment = audio_segment
+        getattr(self, self.effect + "_init")(**kwargs)
+
+    def get_last_gain(self):
+        return getattr(self, self.effect + "_get_last_gain")()
+
+    def get_next_gain(self, current_frame, frame_count):
+        # This returns two values:
+        # - The first one is the gain to apply on that frame
+        # - The last one is True or False depending on whether it is the last
+        #   call to the function and the last gain should be saved permanently
+        return getattr(self, self.effect + "_get_next_gain")(
+                current_frame,
+                frame_count)
+
+    # Fading
+    def fade_init(self, gain=0, **kwargs):
+        self.first_frame = int(self.audio_segment.frame_rate * self.start)
+        self.last_frame = int(self.audio_segment.frame_rate * self.end)
+        self.gain= gain
+
+    def fade_get_last_gain(self):
+        return self.gain
+
+    def fade_get_next_gain(self, current_frame, frame_count):
+        if current_frame >= self.last_frame:
+            return [self.gain, True]
+        elif current_frame < self.first_frame:
+            return [0, False]
+        else:
+            return [
+                    (current_frame - self.first_frame) / \
+                            (self.last_frame - self.first_frame) * self.gain,
+                    False
+                    ]
+
+