AudioBufferProcessor: fix user/bot audio buffers silence padding

CHANGELOG.md

@@ -72,6 +72,9 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Fixed an issue in `AudioBufferProcessor` where user callback would not be
   called on task cancellation.
 
+- Fixed an issue in `AudioBufferProcessor` that would cause wrong silence
+  padding in some cases.
+
 - Fixed an issue where `ElevenLabsTTSService` messages would return a 1009
   websocket error by increasing the max message size limit to 16MB.
 

src/pipecat/processors/audio/audio_buffer_processor.py

@@ -79,14 +79,20 @@ class AudioBufferProcessor(FrameProcessor):
         if isinstance(frame, InputAudioRawFrame):
             resampled = self._resample_audio(frame)
             self._user_audio_buffer.extend(resampled)
-            # Sync the bot's buffer to the user's buffer by adding silence if needed
+            # Sync the bot's buffer to the user's buffer by adding silence if needed.
             if len(self._user_audio_buffer) > len(self._bot_audio_buffer):
-                silence = b"\x00" * len(resampled)
+                missing = len(self._user_audio_buffer) - len(self._bot_audio_buffer)
+                silence = b"\x00" * missing
                 self._bot_audio_buffer.extend(silence)
         # If the bot is speaking, include all audio from the bot.
         elif isinstance(frame, OutputAudioRawFrame):
             resampled = self._resample_audio(frame)
             self._bot_audio_buffer.extend(resampled)
+            # Sync the user's buffer to the bot's buffer by adding silence if needed.
+            if len(self._bot_audio_buffer) > len(self._user_audio_buffer):
+                missing = len(self._bot_audio_buffer) - len(self._user_audio_buffer)
+                silence = b"\x00" * missing
+                self._user_audio_buffer.extend(silence)
 
         if self._buffer_size > 0 and len(self._user_audio_buffer) > self._buffer_size:
             await self._call_on_audio_data_handler()