From 7a5c4192975dfcc5e0faf5764debd272c6173757 Mon Sep 17 00:00:00 2001
From: Grant Sanderson <grant@3blue1brown.com>
Date: Tue, 29 Jan 2019 23:52:56 -0800
Subject: [PATCH] Changed what the gain argument of Scene.play means to instead
 actually apply gain to the passed in sound, not the background

---
 manimlib/scene/scene.py             |  4 ++--
 manimlib/scene/scene_file_writer.py | 30 ++++++++++++++++++++---------
 2 files changed, 23 insertions(+), 11 deletions(-)

diff --git a/manimlib/scene/scene.py b/manimlib/scene/scene.py
index d7977a5a..1f7f9bc1 100644
--- a/manimlib/scene/scene.py
+++ b/manimlib/scene/scene.py
@@ -572,9 +572,9 @@ class Scene(Container):
         for frame in frames:
             self.file_writer.write_frame(frame)
 
-    def add_sound(self, sound_file, time_offset=0, gain=0):
+    def add_sound(self, sound_file, time_offset=0, gain=None, **kwargs):
         time = self.get_time() + time_offset
-        self.file_writer.add_sound(sound_file, time, gain)
+        self.file_writer.add_sound(sound_file, time, gain, **kwargs)
 
     def show_frame(self):
         self.update_frame(ignore_skipping=True)
diff --git a/manimlib/scene/scene_file_writer.py b/manimlib/scene/scene_file_writer.py
index 9ca5664f..cd098afc 100644
--- a/manimlib/scene/scene_file_writer.py
+++ b/manimlib/scene/scene_file_writer.py
@@ -119,7 +119,9 @@ class SceneFileWriter(object):
     def create_audio_segment(self):
         self.audio_segment = AudioSegment.silent()
 
-    def add_audio_segment(self, new_segment, time=None, gain=0):
+    def add_audio_segment(self, new_segment,
+                          time=None,
+                          gain_to_background=None):
         if not self.includes_sound:
             self.includes_sound = True
             self.create_audio_segment()
@@ -140,13 +142,15 @@ class SceneFileWriter(object):
         self.audio_segment = segment.overlay(
             new_segment,
             position=int(1000 * time),
-            gain_during_overlay=gain,
+            gain_during_overlay=gain_to_background,
         )
 
-    def add_sound(self, sound_file, time, gain=0):
+    def add_sound(self, sound_file, time=None, gain=None, **kwargs):
         file_path = get_full_sound_file_path(sound_file)
         new_segment = AudioSegment.from_file(file_path)
-        self.add_audio_segment(new_segment, time, gain)
+        if gain:
+            new_segment = new_segment.apply_gain(gain)
+        self.add_audio_segment(new_segment, time, **kwargs)
 
     # Writers
     def begin_animation(self, allow_write=False):
@@ -307,17 +311,25 @@ class SceneFileWriter(object):
             )
             # Makes sure sound file length will match video file
             self.add_audio_segment(AudioSegment.silent(0))
-            self.audio_segment.export(sound_file_path)
+            self.audio_segment.export(
+                sound_file_path,
+                bitrate='312k',
+            )
             temp_file_path = movie_file_path.replace(".", "_temp.")
-            commands = commands = [
+            commands = [
                 "ffmpeg",
                 "-i", movie_file_path,
                 "-i", sound_file_path,
                 '-y',  # overwrite output file if it exists
-                "-c:v", "copy", "-c:a", "aac",
+                "-c:v", "copy",
+                "-c:a", "aac",
+                "-b:a", "320k",
+                # select video stream from first file
+                "-map", "0:v:0",
+                # select audio stream from second file
+                "-map", "1:a:0",
                 '-loglevel', 'error',
-                "-shortest",
-                "-strict", "experimental",
+                # "-shortest",
                 temp_file_path,
             ]
             subprocess.call(commands)