feat(video_player_android): migrate to Kotlin and improve event handling

- Moved video event processing logic to Dart for better buffer range updates during pause
- Switched Pigeon-generated code to Kotlin for improved type safety
- Added Kotlin plugin and configuration to build.gradle
- Implemented type-safe event channels for internal communication
- Refactored event handling to use dedicated event classes instead of HashMap
- Simplified buffering state management by moving logic to Dart layer

Author: nateshmbhat

packages/video_player/video_player_android/CHANGELOG.md

@@ -2,6 +2,13 @@
 
 * Implements `getAudioTracks()` and `selectAudioTrack()` methods for Android using ExoPlayer.
 
+## 2.8.17
+
+* Moves video event processing logic to Dart, and fixes an issue where buffer
+  range would not be updated for a paused video.
+* Switches to Kotlin for Pigeon-generated code.
+* Adopts type-safe event channels for internal communication.
+
 ## 2.8.16
 
 * Updates Java compatibility version to 17 and minimum supported SDK version to Flutter 3.35/Dart 3.9.

packages/video_player/video_player_android/android/build.gradle

@@ -2,13 +2,15 @@ group = 'io.flutter.plugins.videoplayer'
 version = '1.0-SNAPSHOT'
 
 buildscript {
+    ext.kotlin_version = '2.2.10'
     repositories {
         google()
         mavenCentral()
     }
 
     dependencies {
         classpath 'com.android.tools.build:gradle:8.12.1'
+        classpath "org.jetbrains.kotlin:kotlin-gradle-plugin:$kotlin_version"
     }
 }
 
@@ -20,6 +22,7 @@ rootProject.allprojects {
 }
 
 apply plugin: 'com.android.library'
+apply plugin: 'kotlin-android'
 
 android {
     namespace = "io.flutter.plugins.videoplayer"
@@ -38,6 +41,13 @@ android {
         sourceCompatibility = JavaVersion.VERSION_17
         targetCompatibility = JavaVersion.VERSION_17
     }
+    kotlinOptions {
+        jvmTarget = JavaVersion.VERSION_17.toString()
+    }
+
+    sourceSets {
+        main.java.srcDirs += 'src/main/kotlin'
+    }
 
     dependencies {
         def exoplayer_version = "1.5.1"

packages/video_player/video_player_android/android/src/main/java/io/flutter/plugins/videoplayer/ExoPlayerEventListener.java

@@ -10,7 +10,6 @@
 import androidx.media3.exoplayer.ExoPlayer;
 
 public abstract class ExoPlayerEventListener implements Player.Listener {
-  private boolean isBuffering = false;
   private boolean isInitialized = false;
   protected final ExoPlayer exoPlayer;
   protected final VideoPlayerCallbacks events;
@@ -47,47 +46,34 @@ public ExoPlayerEventListener(
     this.events = events;
   }
 
-  private void setBuffering(boolean buffering) {
-    if (isBuffering == buffering) {
-      return;
-    }
-    isBuffering = buffering;
-    if (buffering) {
-      events.onBufferingStart();
-    } else {
-      events.onBufferingEnd();
-    }
-  }
-
   protected abstract void sendInitialized();
 
   @Override
   public void onPlaybackStateChanged(final int playbackState) {
+    PlatformPlaybackState platformState = PlatformPlaybackState.UNKNOWN;
     switch (playbackState) {
       case Player.STATE_BUFFERING:
-        setBuffering(true);
-        events.onBufferingUpdate(exoPlayer.getBufferedPosition());
+        platformState = PlatformPlaybackState.BUFFERING;
         break;
       case Player.STATE_READY:
+        platformState = PlatformPlaybackState.READY;
         if (!isInitialized) {
           isInitialized = true;
           sendInitialized();
         }
         break;
       case Player.STATE_ENDED:
-        events.onCompleted();
+        platformState = PlatformPlaybackState.ENDED;
         break;
       case Player.STATE_IDLE:
+        platformState = PlatformPlaybackState.IDLE;
         break;
     }
-    if (playbackState != Player.STATE_BUFFERING) {
-      setBuffering(false);
-    }
+    events.onPlaybackStateChanged(platformState);
   }
 
   @Override
   public void onPlayerError(@NonNull final PlaybackException error) {
-    setBuffering(false);
     if (error.errorCode == PlaybackException.ERROR_CODE_BEHIND_LIVE_WINDOW) {
       // See
       // https://exoplayer.dev/live-streaming.html#behindlivewindowexception-and-error_code_behind_live_window

packages/video_player/video_player_android/android/src/main/java/io/flutter/plugins/videoplayer/QueuingEventSink.java

@@ -4,43 +4,39 @@
 
 package io.flutter.plugins.videoplayer;
 
-import io.flutter.plugin.common.EventChannel;
 import java.util.ArrayList;
 
 /**
- * And implementation of {@link EventChannel.EventSink} which can wrap an underlying sink.
+ * A wrapper for {@link PigeonEventSink} which can queue messages.
  *
  * <p>It delivers messages immediately when downstream is available, but it queues messages before
  * the delegate event sink is set with setDelegate.
  *
  * <p>This class is not thread-safe. All calls must be done on the same thread or synchronized
  * externally.
  */
-final class QueuingEventSink implements EventChannel.EventSink {
-  private EventChannel.EventSink delegate;
+final class QueuingEventSink {
+  private PigeonEventSink<PlatformVideoEvent> delegate;
   private final ArrayList<Object> eventQueue = new ArrayList<>();
   private boolean done = false;
 
-  public void setDelegate(EventChannel.EventSink delegate) {
+  public void setDelegate(PigeonEventSink<PlatformVideoEvent> delegate) {
     this.delegate = delegate;
     maybeFlush();
   }
 
-  @Override
   public void endOfStream() {
     enqueue(new EndOfStreamEvent());
     maybeFlush();
     done = true;
   }
 
-  @Override
   public void error(String code, String message, Object details) {
     enqueue(new ErrorEvent(code, message, details));
     maybeFlush();
   }
 
-  @Override
-  public void success(Object event) {
+  public void success(PlatformVideoEvent event) {
     enqueue(event);
     maybeFlush();
   }
@@ -63,7 +59,7 @@ private void maybeFlush() {
         ErrorEvent errorEvent = (ErrorEvent) event;
         delegate.error(errorEvent.code, errorEvent.message, errorEvent.details);
       } else {
-        delegate.success(event);
+        delegate.success((PlatformVideoEvent) event);
       }
     }
     eventQueue.clear();

packages/video_player/video_player_android/android/src/main/java/io/flutter/plugins/videoplayer/VideoPlayer.java

@@ -30,7 +30,7 @@
  *
  * <p>It provides methods to control playback, adjust volume, and handle seeking.
  */
-public abstract class VideoPlayer implements Messages.VideoPlayerInstanceApi {
+public abstract class VideoPlayer implements VideoPlayerInstanceApi {
   @NonNull protected final VideoPlayerCallbacks videoPlayerEvents;
   @Nullable protected final SurfaceProducer surfaceProducer;
   @Nullable private DisposeHandler disposeHandler;
@@ -100,35 +100,37 @@ public void pause() {
   }
 
   @Override
-  public void setLooping(@NonNull Boolean looping) {
+  public void setLooping(boolean looping) {
     exoPlayer.setRepeatMode(looping ? REPEAT_MODE_ALL : REPEAT_MODE_OFF);
   }
 
   @Override
-  public void setVolume(@NonNull Double volume) {
+  public void setVolume(double volume) {
     float bracketedValue = (float) Math.max(0.0, Math.min(1.0, volume));
     exoPlayer.setVolume(bracketedValue);
   }
 
   @Override
-  public void setPlaybackSpeed(@NonNull Double speed) {
+  public void setPlaybackSpeed(double speed) {
     // We do not need to consider pitch and skipSilence for now as we do not handle them and
     // therefore never diverge from the default values.
-    final PlaybackParameters playbackParameters = new PlaybackParameters(speed.floatValue());
+    final PlaybackParameters playbackParameters = new PlaybackParameters((float) speed);
 
     exoPlayer.setPlaybackParameters(playbackParameters);
   }
 
   @Override
-  public @NonNull Messages.PlaybackState getPlaybackState() {
-    return new Messages.PlaybackState.Builder()
-        .setPlayPosition(exoPlayer.getCurrentPosition())
-        .setBufferPosition(exoPlayer.getBufferedPosition())
-        .build();
+  public long getCurrentPosition() {
+    return exoPlayer.getCurrentPosition();
   }
 
   @Override
-  public void seekTo(@NonNull Long position) {
+  public long getBufferedPosition() {
+    return exoPlayer.getBufferedPosition();
+  }
+
+  @Override
+  public void seekTo(long position) {
     exoPlayer.seekTo(position);
   }
 

packages/video_player/video_player_android/android/src/main/java/io/flutter/plugins/videoplayer/VideoPlayerCallbacks.java

@@ -19,13 +19,7 @@
 public interface VideoPlayerCallbacks {
   void onInitialized(int width, int height, long durationInMs, int rotationCorrectionInDegrees);
 
-  void onBufferingStart();
-
-  void onBufferingUpdate(long bufferedPosition);
-
-  void onBufferingEnd();
-
-  void onCompleted();
+  void onPlaybackStateChanged(@NonNull PlatformPlaybackState state);
 
   void onError(@NonNull String code, @Nullable String message, @Nullable Object details);
 

packages/video_player/video_player_android/android/src/main/java/io/flutter/plugins/videoplayer/VideoPlayerEventCallbacks.java

@@ -7,80 +7,51 @@
 import androidx.annotation.NonNull;
 import androidx.annotation.Nullable;
 import androidx.annotation.VisibleForTesting;
-import io.flutter.plugin.common.EventChannel;
-import java.util.HashMap;
-import java.util.Map;
+import io.flutter.plugin.common.BinaryMessenger;
 
 final class VideoPlayerEventCallbacks implements VideoPlayerCallbacks {
-  private final EventChannel.EventSink eventSink;
+  private final QueuingEventSink eventSink;
 
-  static VideoPlayerEventCallbacks bindTo(EventChannel eventChannel) {
+  static VideoPlayerEventCallbacks bindTo(
+      @NonNull BinaryMessenger binaryMessenger, @NonNull String identifier) {
     QueuingEventSink eventSink = new QueuingEventSink();
-    eventChannel.setStreamHandler(
-        new EventChannel.StreamHandler() {
+    VideoEventsStreamHandler.Companion.register(
+        binaryMessenger,
+        new VideoEventsStreamHandler() {
           @Override
-          public void onListen(Object arguments, EventChannel.EventSink events) {
+          public void onListen(
+              Object arguments, @NonNull PigeonEventSink<PlatformVideoEvent> events) {
             eventSink.setDelegate(events);
           }
 
           @Override
           public void onCancel(Object arguments) {
             eventSink.setDelegate(null);
           }
-        });
+        },
+        identifier);
     return VideoPlayerEventCallbacks.withSink(eventSink);
   }
 
   @VisibleForTesting
-  static VideoPlayerEventCallbacks withSink(EventChannel.EventSink eventSink) {
+  static VideoPlayerEventCallbacks withSink(QueuingEventSink eventSink) {
     return new VideoPlayerEventCallbacks(eventSink);
   }
 
-  private VideoPlayerEventCallbacks(EventChannel.EventSink eventSink) {
+  private VideoPlayerEventCallbacks(QueuingEventSink eventSink) {
     this.eventSink = eventSink;
   }
 
   @Override
   public void onInitialized(
       int width, int height, long durationInMs, int rotationCorrectionInDegrees) {
-    Map<String, Object> event = new HashMap<>();
-    event.put("event", "initialized");
-    event.put("width", width);
-    event.put("height", height);
-    event.put("duration", durationInMs);
-    if (rotationCorrectionInDegrees != 0) {
-      event.put("rotationCorrection", rotationCorrectionInDegrees);
-    }
-    eventSink.success(event);
+    eventSink.success(
+        new InitializationEvent(durationInMs, width, height, rotationCorrectionInDegrees));
   }
 
   @Override
-  public void onBufferingStart() {
-    Map<String, Object> event = new HashMap<>();
-    event.put("event", "bufferingStart");
-    eventSink.success(event);
-  }
-
-  @Override
-  public void onBufferingUpdate(long bufferedPosition) {
-    Map<String, Object> event = new HashMap<>();
-    event.put("event", "bufferingUpdate");
-    event.put("position", bufferedPosition);
-    eventSink.success(event);
-  }
-
-  @Override
-  public void onBufferingEnd() {
-    Map<String, Object> event = new HashMap<>();
-    event.put("event", "bufferingEnd");
-    eventSink.success(event);
-  }
-
-  @Override
-  public void onCompleted() {
-    Map<String, Object> event = new HashMap<>();
-    event.put("event", "completed");
-    eventSink.success(event);
+  public void onPlaybackStateChanged(@NonNull PlatformPlaybackState state) {
+    eventSink.success(new PlaybackStateChangeEvent(state));
   }
 
   @Override
@@ -90,9 +61,6 @@ public void onError(@NonNull String code, @Nullable String message, @Nullable Ob
 
   @Override
   public void onIsPlayingStateUpdate(boolean isPlaying) {
-    Map<String, Object> event = new HashMap<>();
-    event.put("event", "isPlayingStateUpdate");
-    event.put("isPlaying", isPlaying);
-    eventSink.success(event);
+    eventSink.success(new IsPlayingStateEvent(isPlaying));
   }
 }