fix(scene): record audio after cached animation replays

manim/renderer/cairo_renderer.py

@@ -71,6 +71,7 @@ def play(
         # Needed when rendering only some animations, and skipping others.
         self.skip_animations = self._original_skipping_status
         self.update_skipping_status()
+        skip_due_to_cache = False
 
         scene.compile_animation_data(*args, **kwargs)
 
@@ -96,6 +97,7 @@ def play(
                         {"hash_current_animation": hash_current_animation},
                     )
                     self.skip_animations = True
+                    skip_due_to_cache = True
                     self.time += scene.duration
         # adding None as a partial movie file will make file_writer ignore the latter.
         self.file_writer.add_partial_movie_file(hash_current_animation)
@@ -121,6 +123,9 @@ def play(
         self.file_writer.end_animation(not self.skip_animations)
 
         self.num_plays += 1
+        if skip_due_to_cache:
+            self.skip_animations = self._original_skipping_status
+            self.update_skipping_status()
 
     def update_frame(  # TODO Description in Docstring
         self,

manim/utils/caching.py

@@ -36,6 +36,7 @@ def handle_caching_play(func: Callable[..., None]) -> Callable[..., None]:
     def wrapper(self: OpenGLRenderer, scene: Scene, *args: Any, **kwargs: Any) -> None:
         self.skip_animations = self._original_skipping_status
         self.update_skipping_status()
+        skip_due_to_cache = False
         animations = scene.compile_animations(*args, **kwargs)
         scene.add_mobjects_from_animations(animations)
         if self.skip_animations:
@@ -60,6 +61,7 @@ def wrapper(self: OpenGLRenderer, scene: Scene, *args: Any, **kwargs: Any) -> No
                     {"hash_play": hash_play},
                 )
                 self.skip_animations = True
+                skip_due_to_cache = True
         else:
             hash_play = f"uncached_{self.num_plays:05}"
         self.animations_hashes.append(hash_play)
@@ -69,5 +71,8 @@ def wrapper(self: OpenGLRenderer, scene: Scene, *args: Any, **kwargs: Any) -> No
             {"h": str(self.animations_hashes[:5])},
         )
         func(self, scene, *args, **kwargs)
+        if skip_due_to_cache:
+            self.skip_animations = self._original_skipping_status
+            self.update_skipping_status()
 
     return wrapper

tests/module/scene/test_sound.py

@@ -4,7 +4,7 @@
 import wave
 from pathlib import Path
 
-from manim import Scene
+from manim import Scene, tempconfig
 
 
 def test_add_sound(tmpdir):
@@ -19,3 +19,30 @@ def test_add_sound(tmpdir):
 
     scene = Scene()
     scene.add_sound(sound_loc)
+
+
+def test_add_sound_after_cached_wait(tmpdir):
+    """Regression test for https://github.com/ManimCommunity/manim/issues/4751."""
+    sound_loc = Path(tmpdir, "noise.wav")
+    with wave.open(str(sound_loc), "w") as f:
+        f.setparams((1, 2, 44100, 0, "NONE", "not compressed"))
+        for _ in range(4410):
+            f.writeframes(struct.pack("h", 1000))
+
+    sounds_recorded: list[int] = []
+
+    class AudioAfterSilenceScene(Scene):
+        def construct(self):
+            self.add_sound(str(sound_loc))
+            self.wait(0.2)
+            self.wait(0.2)
+            self.add_sound(str(sound_loc))
+            sounds_recorded.append(len(self.renderer.file_writer.audio_segment))
+
+    with tempconfig({"media_dir": str(tmpdir), "disable_caching": False}):
+        AudioAfterSilenceScene().render()
+        AudioAfterSilenceScene().render()
+
+    assert len(sounds_recorded) == 2
+    assert sounds_recorded[0] > 0
+    assert sounds_recorded[1] == sounds_recorded[0]