Fix async echo example (#118)

* Fix async example

* Version bump

---------

Co-authored-by: Freddy Boulton <freddyboulton@hf-freddy.local>

backend/fastrtc/tracks.py

@@ -35,6 +35,7 @@ from numpy import typing as npt
 from fastrtc.utils import (
     AdditionalOutputs,
     DataChannel,
+    WebRTCError,
     create_message,
     current_channel,
     player_worker_decode,
@@ -459,6 +460,11 @@ class AudioCallback(AudioStreamTrack):
             if isinstance(self.event_handler, AsyncHandler):
                 callable = self.event_handler.emit
                 start_up = self.event_handler.start_up()
+                if not inspect.isawaitable(start_up):
+                    raise WebRTCError(
+                        "In AsyncStreamHandler, start_up must be a coroutine (async def)"
+                    )
+
             else:
                 callable = functools.partial(
                     loop.run_in_executor, None, self.event_handler_emit

docs/userguide/audio.md

@@ -151,30 +151,30 @@ Here is aa simple example of using `AsyncStreamHandler`:
 
 === "Code"
     ``` py
-
-    from fastrtc import AsyncStreamHandler, wait_for_item
+    from fastrtc import AsyncStreamHandler, wait_for_item, Stream
     import asyncio
+    import numpy as np
 
     class AsyncEchoHandler(AsyncStreamHandler):
-        """Handler for the Gemini API"""
-        
+        """Simple Async Echo Handler"""
+
         def __init__(self) -> None:
-            super().__init__()
+            super().__init__(input_sample_rate=24000)
             self.queue = asyncio.Queue()
 
-        async def receive(self, frame: tuple[int, np.ndarray]) -> None: 
-            self.queue.put(frame)
+        async def receive(self, frame: tuple[int, np.ndarray]) -> None:
+            await self.queue.put(frame)
 
-        async def emit(self) -> None: # (2)
+        async def emit(self) -> None:
             return await wait_for_item(self.queue)
-        
+
         def copy(self):
             return AsyncEchoHandler()
-        
-        async def shutdown(self): # (3)
+
+        async def shutdown(self):
             pass
-        
-        def start_up(self) -> None: # (4)
+
+        async def start_up(self) -> None:
             pass
     ```
 

pyproject.toml

@@ -8,7 +8,7 @@ build-backend = "hatchling.build"
 
 [project]
 name = "fastrtc"
-version = "0.0.9"
+version = "0.0.10"
 description = "The realtime communication library for Python"
 readme = "README.md"
 license = "apache-2.0"