how to enable ear speaker instead of loud speaker in flutter - flutter

Question

I had done with calling peer to peer in flutter but there is a problem how can I enable ear speaker instead of the loudspeaker in a flutter. Please help me to do this,
while establishing calling from one device to another device it only enables the loudspeaker instead of ear speaker. Thanks in advance.
Future<void> joinRoom(String roomId, RTCVideoRenderer remoteVideo) async {
FirebaseFirestore db = FirebaseFirestore.instance;
DocumentReference roomRef = db.collection('rooms').doc('$roomId');
var roomSnapshot = await roomRef.get();
log('Got room ${roomSnapshot.exists}');
if (roomSnapshot.exists) {
log('Create PeerConnection with configuration: $configuration');
peerConnection = await createPeerConnection(configuration);
registerPeerConnectionListeners();
localStream?.getTracks()?.forEach((track) {
peerConnection?.addTrack(track, localStream);
});
// Code for collecting ICE candidates below
var calleeCandidatesCollection = roomRef.collection('calleeCandidates');
peerConnection.onIceCandidate = (RTCIceCandidate candidate) {
if (candidate == null) {
log('onIceCandidate: complete!');
return;
}
log('onIceCandidate: ${candidate.toMap()}');
calleeCandidatesCollection.add(candidate.toMap());
};
// Code for collecting ICE candidate above
peerConnection?.onTrack = (RTCTrackEvent event) {
log('Got remote track: ${event.streams[0]}');
event.streams[0].getTracks().forEach((track) {
log('Add a track to the remoteStream: $track');
remoteStream?.addTrack(track);
});
};
// Code for creating SDP answer below
var data = roomSnapshot.data();
log('Got offer $data');
var offer = data['offer'];
await peerConnection?.setRemoteDescription(
RTCSessionDescription(offer['sdp'], offer['type']),
);
var answer = await peerConnection.createAnswer();
log('Created Answer $answer');
await peerConnection.setLocalDescription(answer);
Map<String, dynamic> roomWithAnswer = {
'answer': {'type': answer.type, 'sdp': answer.sdp}
};
await roomRef.update(roomWithAnswer);
// Finished creating SDP answer
// Listening for remote ICE candidates below
roomRef.collection('callerCandidates').snapshots().listen((snapshot) {
snapshot.docChanges.forEach((document) {
var data = document.doc.data();
// log(data);
log('Got new remote ICE candidate: $data');
peerConnection.addCandidate(
RTCIceCandidate(
data['candidate'],
data['sdpMid'],
data['sdpMLineIndex'],
),
);
});
});
}
}
Future<void> openUserMedia(RTCVideoRenderer localVideo,
RTCVideoRenderer remoteVideo, BuildContext contextt) async {
context = contextt;
chatProvider = Provider.of<ChatProvider>(context, listen: false);
var stream = await navigator.mediaDevices.getUserMedia({'audio': true});
localVideo.srcObject = stream;
localStream = stream;
remoteVideo.srcObject = await createLocalMediaStream('key');
}