fix: Use audio_in_sample_rate to deserialize data for TwilioFrameSerializer

CHANGELOG.md

@@ -5,6 +5,14 @@ All notable changes to **Pipecat** will be documented in this file.
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
+## [Unreleased]
+
+### Fixed
+
+- Fixed an issue with the `TwilioFrameSerializer` where
+  `frame.audio_out_sample_rate` was incorrectly used in place of
+  `frame.audio_in_sample_rate`.
+
 ## [0.0.55] - 2025-02-05
 
 ### Added

src/pipecat/serializers/twilio.py

@@ -27,15 +27,15 @@ from pipecat.serializers.base_serializer import FrameSerializer, FrameSerializer
 
 class TwilioFrameSerializer(FrameSerializer):
     class InputParams(BaseModel):
-        twilio_sample_rate: Optional[int] = None
-        sample_rate: Optional[int] = None
+        twilio_sample_rate: Optional[int] = None  # Default Twilio rate (8kHz)
+        sample_rate: Optional[int] = None  # Pipeline input rate
 
     def __init__(self, stream_sid: str, params: InputParams = InputParams()):
         self._stream_sid = stream_sid
         self._params = params
 
-        self._twilio_sample_rate = 0
-        self._sample_rate = 0
+        self._twilio_sample_rate = 0  # Fixed rate for Twilio (8kHz)
+        self._sample_rate = 0  # Pipeline input rate
 
         self._resampler = create_default_resampler()
 
@@ -44,8 +44,9 @@ class TwilioFrameSerializer(FrameSerializer):
         return FrameSerializerType.TEXT
 
     async def setup(self, frame: StartFrame):
+        # Configure rates for input path: Twilio (8kHz μ-law) -> Pipeline (PCM)
         self._twilio_sample_rate = self._params.twilio_sample_rate or frame.audio_in_sample_rate
-        self._sample_rate = self._params.sample_rate or frame.audio_out_sample_rate
+        self._sample_rate = self._params.sample_rate or frame.audio_in_sample_rate
 
     async def serialize(self, frame: Frame) -> str | bytes | None:
         if isinstance(frame, StartInterruptionFrame):
@@ -54,6 +55,7 @@ class TwilioFrameSerializer(FrameSerializer):
         elif isinstance(frame, AudioRawFrame):
             data = frame.audio
 
+            # Output: Convert PCM at frame's rate to 8kHz μ-law for Twilio
             serialized_data = await pcm_to_ulaw(
                 data, frame.sample_rate, self._twilio_sample_rate, self._resampler
             )
@@ -75,6 +77,7 @@ class TwilioFrameSerializer(FrameSerializer):
             payload_base64 = message["media"]["payload"]
             payload = base64.b64decode(payload_base64)
 
+            # Input: Convert Twilio's 8kHz μ-law to PCM at pipeline input rate
             deserialized_data = await ulaw_to_pcm(
                 payload, self._twilio_sample_rate, self._sample_rate, self._resampler
             )