feat: Support setVideoFPS for subscribe. (#258)

* feat: Support setVideoFPS for subscribe.

* Update lib/src/publication/remote.dart

Co-authored-by: David Zhao <dz@livekit.io>

* Add comment for setVideoFPS.

---------

Co-authored-by: David Zhao <dz@livekit.io>

example/lib/widgets/participant.dart

@@ -199,17 +199,22 @@ class _RemoteParticipantWidgetState
           mainAxisSize: MainAxisSize.max,
           mainAxisAlignment: MainAxisAlignment.end,
           children: [
+            // Menu for RemoteTrackPublication<RemoteAudioTrack>
+            if (firstAudioPublication != null && !isScreenShare)
+              RemoteTrackPublicationMenuWidget(
+                pub: firstAudioPublication!,
+                icon: EvaIcons.volumeUp,
+              ),
             // Menu for RemoteTrackPublication<RemoteVideoTrack>
             if (videoPublication != null)
               RemoteTrackPublicationMenuWidget(
                 pub: videoPublication!,
                 icon: isScreenShare ? EvaIcons.monitor : EvaIcons.video,
               ),
-            // Menu for RemoteTrackPublication<RemoteAudioTrack>
+            if (videoPublication != null)
-            if (firstAudioPublication != null && !isScreenShare)
+              RemoteTrackFPSMenuWidget(
-              RemoteTrackPublicationMenuWidget(
+                pub: videoPublication!,
-                pub: firstAudioPublication!,
+                icon: EvaIcons.options2,
-                icon: EvaIcons.volumeUp,
               ),
           ],
         ),
@@ -253,3 +258,37 @@ class RemoteTrackPublicationMenuWidget extends StatelessWidget {
         ),
       );
 }
+
+class RemoteTrackFPSMenuWidget extends StatelessWidget {
+  final IconData icon;
+  final RemoteTrackPublication pub;
+  const RemoteTrackFPSMenuWidget({
+    required this.pub,
+    required this.icon,
+    Key? key,
+  }) : super(key: key);
+
+  @override
+  Widget build(BuildContext context) => Material(
+        color: Colors.black.withOpacity(0.3),
+        child: PopupMenuButton<Function>(
+          tooltip: 'PreferredFPS',
+          icon: Icon(icon, color: Colors.white),
+          onSelected: (value) => value(),
+          itemBuilder: (BuildContext context) => <PopupMenuEntry<Function>>[
+            PopupMenuItem(
+              child: const Text('30'),
+              value: () => pub.setVideoFPS(30),
+            ),
+            PopupMenuItem(
+              child: const Text('15'),
+              value: () => pub.setVideoFPS(15),
+            ),
+            PopupMenuItem(
+              child: const Text('8'),
+              value: () => pub.setVideoFPS(8),
+            ),
+          ],
+        ),
+      );
+}

lib/src/publication/remote.dart

@@ -31,6 +31,10 @@ class RemoteTrackPublication<T extends RemoteTrack>
   bool get enabled => _enabled;
   bool _enabled = true;
 
+  /// The current desired FPS of the track. This is only available for video tracks that support SVC.
+  int? _fps;
+  int get fps => _fps ?? 0;
+
   lk_models.VideoQuality _videoQuality = lk_models.VideoQuality.HIGH;
   lk_models.VideoQuality get videoQuality => _videoQuality;
 
@@ -227,6 +231,14 @@ class RemoteTrackPublication<T extends RemoteTrack>
     sendUpdateTrackSettings();
   }
 
+  /// Set desired FPS, server will do its best to return FPS close to this.
+  /// It's only supported for video codecs that support SVC currently.
+  Future<void> setVideoFPS(int newValue) async {
+    if (newValue == _fps) return;
+    _fps = newValue;
+    sendUpdateTrackSettings();
+  }
+
   Future<void> enable() async {
     if (_enabled) return;
     _enabled = true;
@@ -289,6 +301,7 @@ class RemoteTrackPublication<T extends RemoteTrack>
     );
     if (kind == lk_models.TrackType.VIDEO) {
       settings.quality = _videoQuality;
+      if (_fps != null) settings.fps = _fps!;
     }
     participant.room.engine.signalClient.sendUpdateTrackSettings(settings);
   }