Stop audio mixer on pipeline cancellation to prevent 100% CPU usage

changelog/2955.fixed.md

@@ -0,0 +1 @@
+- Fixed audio mixer not being stopped on pipeline cancellation, causing 100% CPU usage after call disconnect.

src/pipecat/transports/base_output.py

@@ -504,6 +504,10 @@ class BaseOutputTransport(FrameProcessor):
             await self._cancel_clock_task()
             await self._cancel_video_task()
 
+            # Stop audio mixer so it doesn't keep generating frames after cancellation.
+            if self._mixer:
+                await self._mixer.stop()
+
         async def handle_interruptions(self, _: InterruptionFrame):
             """Handle interruption events by restarting tasks and clearing buffers.