SoundfileMixer: add mixing argument and require keywords

CHANGELOG.md

@@ -8,9 +8,18 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+### Added
+
+- It is now possible to disable `SoundfileMixer` when created. You can then use
+  `MixerEnableFrame` to dynamically enable it when necessary.
+
+### Changed
+
+- `SoundfileMixer` constructor arguments need to be keywords.
+
 ### Fixed
 
-- Fixed an issue in `SmallWebRTCTransport` where an error was thrown if the 
+- Fixed an issue in `SmallWebRTCTransport` where an error was thrown if the
   client did not create a video transceiver.
 
 ## [0.0.63] - 2025-04-11

src/pipecat/audio/mixers/soundfile_mixer.py

@@ -38,9 +38,11 @@ class SoundfileMixer(BaseAudioMixer):
 
     def __init__(
         self,
+        *,
         sound_files: Mapping[str, str],
         default_sound: str,
         volume: float = 0.4,
+        mixing: bool = True,
         loop: bool = True,
         **kwargs,
     ):
@@ -52,7 +54,7 @@ class SoundfileMixer(BaseAudioMixer):
         self._sound_pos = 0
         self._sounds: Dict[str, Any] = {}
         self._current_sound = default_sound
-        self._mixing = True
+        self._mixing = mixing
         self._loop = loop
 
     async def start(self, sample_rate: int):