diff --git a/src/pipecat/serializers/twilio.py b/src/pipecat/serializers/twilio.py
index 5ac6227dd..ea7a562aa 100644
--- a/src/pipecat/serializers/twilio.py
+++ b/src/pipecat/serializers/twilio.py
@@ -1,3 +1,9 @@
+#
+# Copyright (c) 2024, Daily
+#
+# SPDX-License-Identifier: BSD 2-Clause License
+#
+
 import base64
 import json
 
@@ -12,29 +18,36 @@ class TwilioFrameSerializer(FrameSerializer):
     }
 
     def __init__(self):
-        self.sid = None
+        self._sid = None
 
+    def serialize(self, frame: Frame) -> str | bytes | None:
+        if not isinstance(frame, AudioRawFrame):
+            return None
 
-    def serialize(self, frame: AudioRawFrame) -> dict:
         data = frame.audio
 
         serialized_data = pcm_16000_to_ulaw_8000(data)
-        payload = base64.b64encode(serialized_data).decode('utf-8')
-        answer_dict = {"event": "media",
-                       "streamSid": self.sid,
-                       "media": {"payload": payload}}
+        payload = base64.b64encode(serialized_data).decode("utf-8")
+        answer = {
+            "event": "media",
+            "streamSid": self._sid,
+            "media": {
+                "payload": payload
+            }
+        }
 
-        return answer_dict
+        return json.dumps(answer)
 
-    def deserialize(self, message: bytes) -> AudioRawFrame | None:
-        data = json.loads(message)
-        if not self.sid:
-            self.sid = data['streamSid'] if data.get("streamSid") else None
+    def deserialize(self, data: str | bytes) -> Frame | None:
+        message = json.loads(data)
 
-        if data['event'] != 'media':
+        if not self._sid:
+            self._sid = message["streamSid"] if "streamSid" in message else None
+
+        if message["event"] != "media":
             return None
         else:
-            payload_base64 = data['media']['payload']
+            payload_base64 = message["media"]["payload"]
             payload = base64.b64decode(payload_base64)
 
             deserialized_data = ulaw_8000_to_pcm_16000(payload)
diff --git a/src/pipecat/transports/network/fastapi_websocket.py b/src/pipecat/transports/network/fastapi_websocket.py
index fedcd9b4c..6e5307780 100644
--- a/src/pipecat/transports/network/fastapi_websocket.py
+++ b/src/pipecat/transports/network/fastapi_websocket.py
@@ -1,12 +1,18 @@
+#
+# Copyright (c) 2024, Daily
+#
+# SPDX-License-Identifier: BSD 2-Clause License
+#
+
+
 import asyncio
 import io
 import wave
-from fastapi import WebSocket
 
 from typing import Awaitable, Callable
 from pydantic.main import BaseModel
 
-from pipecat.serializers.TwilioFrameSerializer import TwilioFrameSerializer
+from pipecat.serializers.twilio import TwilioFrameSerializer
 from pipecat.frames.frames import AudioRawFrame, StartFrame
 from pipecat.processors.frame_processor import FrameProcessor
 from pipecat.serializers.base_serializer import FrameSerializer
@@ -16,6 +22,15 @@ from pipecat.transports.base_transport import BaseTransport, TransportParams
 
 from loguru import logger
 
+try:
+    from fastapi import WebSocket
+    from starlette.websockets import WebSocketState
+except ModuleNotFoundError as e:
+    logger.error(f"Exception: {e}")
+    logger.error(
+        "In order to use FastAPI websockets, you need to `pip install pipecat-ai[websocket]`.")
+    raise Exception(f"Missing module: {e}")
+
 
 class FastAPIWebsocketParams(TransportParams):
     add_wav_header: bool = False
@@ -30,7 +45,12 @@ class FastAPIWebsocketCallbacks(BaseModel):
 
 class FastAPIWebsocketInputTransport(BaseInputTransport):
 
-    def __init__(self, websocket: WebSocket, params: FastAPIWebsocketParams, callbacks: FastAPIWebsocketCallbacks, **kwargs):
+    def __init__(
+            self,
+            websocket: WebSocket,
+            params: FastAPIWebsocketParams,
+            callbacks: FastAPIWebsocketCallbacks,
+            **kwargs):
         super().__init__(params, **kwargs)
 
         self._websocket = websocket
@@ -43,7 +63,8 @@ class FastAPIWebsocketInputTransport(BaseInputTransport):
         self._receive_task = self.get_event_loop().create_task(self._receive_messages())
 
     async def stop(self):
-        await self._websocket.close()
+        if self._websocket.client_state != WebSocketState.DISCONNECTED:
+            await self._websocket.close()
         await super().stop()
 
     async def _receive_messages(self):
@@ -58,6 +79,7 @@ class FastAPIWebsocketInputTransport(BaseInputTransport):
 
         await self._callbacks.on_client_disconnected(self._websocket)
 
+
 class FastAPIWebsocketOutputTransport(BaseOutputTransport):
 
     def __init__(self, websocket: WebSocket, params: FastAPIWebsocketParams, **kwargs):
@@ -92,17 +114,23 @@ class FastAPIWebsocketOutputTransport(BaseOutputTransport):
                 frame = wav_frame
 
             payload = self._params.serializer.serialize(frame)
-
-            future = asyncio.run_coroutine_threadsafe(
-                self._websocket.send_json(payload), self.get_event_loop())
-            future.result()
+            if payload:
+                future = asyncio.run_coroutine_threadsafe(
+                    self._websocket.send_text(payload), self.get_event_loop())
+                future.result()
 
             self._audio_buffer = self._audio_buffer[self._params.audio_frame_size:]
 
 
 class FastAPIWebsocketTransport(BaseTransport):
 
-    def __init__(self, websocket: WebSocket, params: FastAPIWebsocketParams = FastAPIWebsocketParams(), input_name: str | None = None, output_name: str | None = None, loop: asyncio.AbstractEventLoop | None = None):
+    def __init__(
+            self,
+            websocket: WebSocket,
+            params: FastAPIWebsocketParams = FastAPIWebsocketParams(),
+            input_name: str | None = None,
+            output_name: str | None = None,
+            loop: asyncio.AbstractEventLoop | None = None):
         super().__init__(input_name=input_name, output_name=output_name, loop=loop)
         self._params = params
 
@@ -111,8 +139,10 @@ class FastAPIWebsocketTransport(BaseTransport):
             on_client_disconnected=self._on_client_disconnected
         )
 
-        self._input = FastAPIWebsocketInputTransport(websocket, self._params, self._callbacks, name=self._input_name)
-        self._output = FastAPIWebsocketOutputTransport(websocket, self._params, name=self._output_name)
+        self._input = FastAPIWebsocketInputTransport(
+            websocket, self._params, self._callbacks, name=self._input_name)
+        self._output = FastAPIWebsocketOutputTransport(
+            websocket, self._params, name=self._output_name)
 
         # Register supported handlers. The user will only be able to register
         # these handlers.