feat: add Transcription Event. (#531)

* feat: add Transcription Event.

* dart format.

* remove deprecated API.

* print seg.text in example app.

Author: cloudwebrtc

example/lib/widgets/participant.dart

@@ -84,17 +84,26 @@ abstract class _ParticipantWidgetState<T extends ParticipantWidget>
   TrackPublication? get videoPublication;
   TrackPublication? get audioPublication;
   bool get isScreenShare => widget.type == ParticipantTrackType.kScreenShare;
+  EventsListener<ParticipantEvent>? _listener;
 
   @override
   void initState() {
     super.initState();
+    _listener = widget.participant.createListener();
+    _listener?.on<TranscriptionEvent>((e) {
+      for (var seg in e.segments) {
+        print('Transcription: ${seg.text} ${seg.isFinal}');
+      }
+    });
+
     widget.participant.addListener(_onParticipantChanged);
     _onParticipantChanged();
   }
 
   @override
   void dispose() {
     widget.participant.removeListener(_onParticipantChanged);
+    _listener?.dispose();
     super.dispose();
   }
 

lib/src/core/engine.dart

@@ -616,6 +616,18 @@ class Engine extends Disposable with EventsEmittable<EngineEvent> {
         packet: dp.user,
         kind: dp.kind,
       ));
+    } else if (dp.whichValue() == lk_models.DataPacket_Value.transcription) {
+      // Transcription packet
+      events.emit(EngineTranscriptionReceivedEvent(
+        transcription: dp.transcription,
+      ));
+    } else if (dp.whichValue() == lk_models.DataPacket_Value.sipDtmf) {
+      // SIP DTMF packet
+      events.emit(EngineSipDtmfReceivedEvent(
+        dtmf: dp.sipDtmf,
+      ));
+    } else {
+      logger.warning('Unknown data packet type: ${dp.whichValue()}');
     }
   }
 

lib/src/core/room.dart

@@ -436,6 +436,7 @@ class Room extends DisposableChangeNotifier with EventsEmittable<RoomEvent> {
     ..on<EngineActiveSpeakersUpdateEvent>(
         (event) => _onEngineActiveSpeakersUpdateEvent(event.speakers))
     ..on<EngineDataPacketReceivedEvent>(_onDataMessageEvent)
+    ..on<EngineTranscriptionReceivedEvent>(_onTranscriptionEvent)
     ..on<AudioPlaybackStarted>((event) {
       _handleAudioPlaybackStarted();
     })
@@ -683,6 +684,37 @@ class Room extends DisposableChangeNotifier with EventsEmittable<RoomEvent> {
     }
   }
 
+  void _onTranscriptionEvent(EngineTranscriptionReceivedEvent event) {
+    final participant = getParticipantByIdentity(
+        event.transcription.transcribedParticipantIdentity);
+    if (participant == null) {
+      return;
+    }
+
+    final publication =
+        participant.getTrackPublicationBySid(event.transcription.trackId);
+
+    var segments = event.transcription.segments.map((e) {
+      return TranscriptionSegment(
+        text: e.text,
+        id: e.id,
+        startTime: DateTime.fromMillisecondsSinceEpoch(e.startTime.toInt()),
+        endTime: DateTime.fromMillisecondsSinceEpoch(e.endTime.toInt()),
+        isFinal: e.final_5,
+        language: e.language,
+      );
+    }).toList();
+
+    final transcription = TranscriptionEvent(
+      participant: participant,
+      publication: publication,
+      segments: segments,
+    );
+
+    participant.events.emit(transcription);
+    events.emit(transcription);
+  }
+
   void _onDataMessageEvent(EngineDataPacketReceivedEvent dataPacketEvent) {
     // participant may be null if data is sent from Server-API
     final senderSid = dataPacketEvent.packet.participantSid;

lib/src/events.dart

@@ -433,6 +433,35 @@ class ParticipantPermissionsUpdatedEvent with RoomEvent, ParticipantEvent {
       '(participant: ${participant}, permissions: ${permissions})';
 }
 
+class TranscriptionSegment {
+  final String id;
+  final String text;
+  final DateTime startTime;
+  final DateTime endTime;
+  final bool isFinal;
+  final String language;
+  const TranscriptionSegment({
+    required this.id,
+    required this.text,
+    required this.startTime,
+    required this.endTime,
+    required this.isFinal,
+    required this.language,
+  });
+}
+
+/// Transcription event received from the server.
+class TranscriptionEvent with RoomEvent, ParticipantEvent {
+  final Participant participant;
+  final TrackPublication<Track>? publication;
+  final List<TranscriptionSegment> segments;
+  const TranscriptionEvent({
+    required this.participant,
+    required this.publication,
+    required this.segments,
+  });
+}
+
 class ParticipantNameUpdatedEvent with RoomEvent, ParticipantEvent {
   final Participant participant;
   final String name;

lib/src/internal/events.dart

@@ -410,6 +410,22 @@ class EngineDataPacketReceivedEvent with EngineEvent, InternalEvent {
   });
 }
 
+@internal
+class EngineTranscriptionReceivedEvent with EngineEvent, InternalEvent {
+  final lk_models.Transcription transcription;
+  const EngineTranscriptionReceivedEvent({
+    required this.transcription,
+  });
+}
+
+@internal
+class EngineSipDtmfReceivedEvent with EngineEvent, InternalEvent {
+  final lk_models.SipDTMF dtmf;
+  const EngineSipDtmfReceivedEvent({
+    required this.dtmf,
+  });
+}
+
 @internal
 abstract class DataChannelStateUpdatedEvent with EngineEvent, InternalEvent {
   final bool isPrimary;