BaseOutputTransport: only push downstream if transport write successful

Fixes #2589

CHANGELOG.md

@@ -68,6 +68,10 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ### Changed
 
+- `BaseOutputTransport` methods `write_audio_frame` and `write_video_frame` now
+  return a boolean to indicate if the transport implementation was able to write
+  the given frame or not.
+
 - Updated Silero VAD model to v6.
 
 - Updated `livekit` to 1.0.13.
@@ -98,6 +102,9 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ### Fixed
 
+- Fixed a `BaseOutputTransport` issue that could produce large saved
+  `AudioBufferProcessor` files when using an audio mixer.
+
 - Fixed a `PipelineRunner` issue on Windows where setting up SIGINT and SIGTERM
   was raising an exception.