Not serializing a JSON in case we have no audio.

src/pipecat/serializers/exotel.py

@@ -108,6 +108,10 @@ class ExotelFrameSerializer(FrameSerializer):
             serialized_data = await self._output_resampler.resample(
                 data, frame.sample_rate, self._exotel_sample_rate
             )
+            if serialized_data is None or len(serialized_data) == 0:
+                # Ignoring in case we don't have audio
+                return None
+
             payload = base64.b64encode(serialized_data).decode("ascii")
 
             answer = {

src/pipecat/serializers/plivo.py

@@ -132,6 +132,10 @@ class PlivoFrameSerializer(FrameSerializer):
             serialized_data = await pcm_to_ulaw(
                 data, frame.sample_rate, self._plivo_sample_rate, self._output_resampler
             )
+            if serialized_data is None or len(serialized_data) == 0:
+                # Ignoring in case we don't have audio
+                return None
+
             payload = base64.b64encode(serialized_data).decode("utf-8")
             answer = {
                 "event": "playAudio",

src/pipecat/serializers/telnyx.py

@@ -155,6 +155,10 @@ class TelnyxFrameSerializer(FrameSerializer):
             else:
                 raise ValueError(f"Unsupported encoding: {self._params.inbound_encoding}")
 
+            if serialized_data is None or len(serialized_data) == 0:
+                # Ignoring in case we don't have audio
+                return None
+
             payload = base64.b64encode(serialized_data).decode("utf-8")
             answer = {
                 "event": "media",

src/pipecat/serializers/twilio.py

@@ -13,11 +13,7 @@ from typing import Optional
 from loguru import logger
 from pydantic import BaseModel
 
-from pipecat.audio.utils import (
+from pipecat.audio.utils import create_stream_resampler, pcm_to_ulaw, ulaw_to_pcm
-    create_stream_resampler,
-    pcm_to_ulaw,
-    ulaw_to_pcm,
-)
 from pipecat.frames.frames import (
     AudioRawFrame,
     CancelFrame,
@@ -136,6 +132,10 @@ class TwilioFrameSerializer(FrameSerializer):
             serialized_data = await pcm_to_ulaw(
                 data, frame.sample_rate, self._twilio_sample_rate, self._output_resampler
             )
+            if serialized_data is None or len(serialized_data) == 0:
+                # Ignoring in case we don't have audio
+                return None
+
             payload = base64.b64encode(serialized_data).decode("utf-8")
             answer = {
                 "event": "media",