[Python] No audio in the final video when converting webm blobs to mp4 using ffmpeg

I trying to record user camera and microphone and using MediaRecorder to convert the stream to blobs and sending the blobs every 2 second to the backend using websocket. Everything is working fine, but when I checked the final mp4 video in the backend, it doesn't have any audio to it, I try specifying the audio codec, but still no help.

My frontend code :-

const micStream = await navigator.mediaDevices.getUserMedia({ audio: true });

const recorder = new MediaRecorder(stream, {
mimeType: 'video/webm;codecs=H264',
videoBitsPerSecond: 8000000,
audioBitsPerSecond : 8000000
});

recorder.ondataavailable = (e: BlobEvent) => {
websocket.send(e.data)
}
recorder.start(2000);


And here is the backend code :-

@router.websocket("/streamaudio")
async def websocket_endpoint(websocket: WebSocket):
await manager.connect(websocket)

recordingFile = os.path.join(os.getcwd(), f"recording_.mp4")

command = [
'ffmpeg',
'-y',
'-i',
'-',
'-codec:v',
'copy',
'-c:a', 'aac',
'-y',
'-f', 'mp4',
recordingFile,
# "-"
# f'output{queueNumber}.mp4',
]


try:
while True:
try:

data = await websocket.receive_bytes()

process.stdin.send(data)

except RuntimeError:
break
except WebSocketDisconnect:
print(f"Client disconnected: {websocket.client.host}")
finally:
manager.disconnect(websocket)
await process.stdin.aclose()
await process.wait()

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