Move flush_audio to WebsocketTTSService base class

CHANGELOG.md

@@ -65,6 +65,16 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Added `AzureRealtimeBetaLLMService` to support Azure's OpeanAI Realtime API. Added
   foundational example `19a-azure-realtime-beta.py`.
 
+### Changed
+
+- Moved `flush_audio()` from the `TTSService` base class to
+  `WebsocketTTSService`.
+
+### Fixed
+
+- Fixed an issue in `GoogleSTTService`, where it didn't have a `set_language`
+  function. This required a name change from `set_languages` to `set_language`.
+
 ## [0.0.58] - 2025-02-26
 
 ### Added

src/pipecat/services/ai_services.py

@@ -270,10 +270,6 @@ class TTSService(AIService):
     def set_voice(self, voice: str):
         self._voice_id = voice
 
-    @abstractmethod
-    async def flush_audio(self):
-        pass
-
     # Converts the text to audio.
     @abstractmethod
     async def run_tts(self, text: str) -> AsyncGenerator[Frame, None]:
@@ -539,6 +535,11 @@ class WebsocketTTSService(TTSService, WebsocketService):
         TTSService.__init__(self, **kwargs)
         WebsocketService.__init__(self)
 
+    @abstractmethod
+    async def flush_audio(self):
+        """Flush any buffered audio in this websocket-based TTS service."""
+        pass
+
 
 class InterruptibleTTSService(WebsocketTTSService):
     """This is a base class for websocket-based TTS services that don't support