Allow multiple Transformer listeners to be registered.

Multiple listeners can be added to Transformer and its builder.
All or specific listeners can also be removed.

PiperOrigin-RevId: 421047650

libraries/common/src/main/java/androidx/media3/common/util/ListenerSet.java

@@ -118,6 +118,21 @@ public final class ListenerSet<T extends @NonNull Object> {
    */
   @CheckResult
   public ListenerSet<T> copy(Looper looper, IterationFinishedEvent<T> iterationFinishedEvent) {
+    return copy(looper, clock, iterationFinishedEvent);
+  }
+
+  /**
+   * Copies the listener set.
+   *
+   * @param looper The new {@link Looper} for the copied listener set.
+   * @param clock The new {@link Clock} for the copied listener set.
+   * @param iterationFinishedEvent The new {@link IterationFinishedEvent} sent when all other events
+   *     sent during one {@link Looper} message queue iteration were handled by the listeners.
+   * @return The copied listener set.
+   */
+  @CheckResult
+  public ListenerSet<T> copy(
+      Looper looper, Clock clock, IterationFinishedEvent<T> iterationFinishedEvent) {
     return new ListenerSet<>(listeners, looper, clock, iterationFinishedEvent);
   }
 
@@ -152,6 +167,11 @@ public final class ListenerSet<T extends @NonNull Object> {
     }
   }
 
+  /** Removes all listeners from the set. */
+  public void clear() {
+    listeners.clear();
+  }
+
   /** Returns the number of added listeners. */
   public int size() {
     return listeners.size();

libraries/transformer/src/androidTest/java/androidx/media3/transformer/mh/AndroidTestUtil.java

@@ -72,7 +72,7 @@ import org.checkerframework.checker.nullness.compatqual.NullableType;
     Transformer testTransformer =
         transformer
             .buildUpon()
-            .setListener(
+            .addListener(
                 new Transformer.Listener() {
                   @Override
                   public void onTransformationCompleted(MediaItem inputMediaItem) {

libraries/transformer/src/main/java/androidx/media3/transformer/Transformer.java

@@ -43,6 +43,7 @@ import androidx.media3.common.Player;
 import androidx.media3.common.Timeline;
 import androidx.media3.common.TracksInfo;
 import androidx.media3.common.util.Clock;
+import androidx.media3.common.util.ListenerSet;
 import androidx.media3.common.util.UnstableApi;
 import androidx.media3.common.util.Util;
 import androidx.media3.exoplayer.DefaultLoadControl;
@@ -100,7 +101,7 @@ public final class Transformer {
     private boolean removeVideo;
     private String containerMimeType;
     private TransformationRequest transformationRequest;
-    private Transformer.Listener listener;
+    private ListenerSet<Transformer.Listener> listeners;
     private DebugViewProvider debugViewProvider;
     private Looper looper;
     private Clock clock;
@@ -110,9 +111,9 @@ public final class Transformer {
     @Deprecated
     public Builder() {
       muxerFactory = new FrameworkMuxer.Factory();
-      listener = new Listener() {};
       looper = Util.getCurrentOrMainLooper();
       clock = Clock.DEFAULT;
+      listeners = new ListenerSet<>(looper, clock, (listener, flags) -> {});
       encoderFactory = Codec.EncoderFactory.DEFAULT;
       debugViewProvider = DebugViewProvider.NONE;
       containerMimeType = MimeTypes.VIDEO_MP4;
@@ -127,9 +128,9 @@ public final class Transformer {
     public Builder(Context context) {
       this.context = context.getApplicationContext();
       muxerFactory = new FrameworkMuxer.Factory();
-      listener = new Listener() {};
       looper = Util.getCurrentOrMainLooper();
       clock = Clock.DEFAULT;
+      listeners = new ListenerSet<>(looper, clock, (listener, flags) -> {});
       encoderFactory = Codec.EncoderFactory.DEFAULT;
       debugViewProvider = DebugViewProvider.NONE;
       containerMimeType = MimeTypes.VIDEO_MP4;
@@ -145,7 +146,7 @@ public final class Transformer {
       this.removeVideo = transformer.removeVideo;
       this.containerMimeType = transformer.containerMimeType;
       this.transformationRequest = transformer.transformationRequest;
-      this.listener = transformer.listener;
+      this.listeners = transformer.listeners;
       this.looper = transformer.looper;
       this.encoderFactory = transformer.encoderFactory;
       this.debugViewProvider = transformer.debugViewProvider;
@@ -267,15 +268,51 @@ public final class Transformer {
     }
 
     /**
-     * Sets the {@link Transformer.Listener} to listen to the transformation events.
+     * @deprecated Use {@link #addListener(Listener)}, {@link #removeListener(Listener)} or {@link
+     *     #removeAllListeners()} instead.
+     */
+    @Deprecated
+    public Builder setListener(Transformer.Listener listener) {
+      this.listeners.clear();
+      this.listeners.add(listener);
+      return this;
+    }
+
+    /**
+     * Adds a {@link Transformer.Listener} to listen to the transformation events.
      *
-     * <p>This is equivalent to {@link Transformer#setListener(Listener)}.
+     * <p>This is equivalent to {@link Transformer#addListener(Listener)}.
      *
      * @param listener A {@link Transformer.Listener}.
      * @return This builder.
      */
-    public Builder setListener(Transformer.Listener listener) {
+    public Builder addListener(Transformer.Listener listener) {
-      this.listener = listener;
+      this.listeners.add(listener);
+      return this;
+    }
+
+    /**
+     * Removes a {@link Transformer.Listener}.
+     *
+     * <p>This is equivalent to {@link Transformer#removeListener(Listener)}.
+     *
+     * @param listener A {@link Transformer.Listener}.
+     * @return This builder.
+     */
+    public Builder removeListener(Transformer.Listener listener) {
+      this.listeners.remove(listener);
+      return this;
+    }
+
+    /**
+     * Removes all {@link Transformer.Listener listeners}.
+     *
+     * <p>This is equivalent to {@link Transformer#removeAllListeners()}.
+     *
+     * @return This builder.
+     */
+    public Builder removeAllListeners() {
+      this.listeners.clear();
       return this;
     }
 
@@ -290,6 +327,7 @@ public final class Transformer {
      */
     public Builder setLooper(Looper looper) {
       this.looper = looper;
+      this.listeners = listeners.copy(looper, (listener, flags) -> {});
       return this;
     }
 
@@ -330,6 +368,7 @@ public final class Transformer {
     @VisibleForTesting
     /* package */ Builder setClock(Clock clock) {
       this.clock = clock;
+      this.listeners = listeners.copy(looper, clock, (listener, flags) -> {});
       return this;
     }
 
@@ -383,7 +422,7 @@ public final class Transformer {
           removeVideo,
           containerMimeType,
           transformationRequest,
-          listener,
+          listeners,
           looper,
           clock,
           encoderFactory,
@@ -482,8 +521,8 @@ public final class Transformer {
   private final Codec.EncoderFactory encoderFactory;
   private final Codec.DecoderFactory decoderFactory;
   private final Transformer.DebugViewProvider debugViewProvider;
+  private final ListenerSet<Transformer.Listener> listeners;
 
-  private Transformer.Listener listener;
   @Nullable private MuxerWrapper muxerWrapper;
   @Nullable private ExoPlayer player;
   @ProgressState private int progressState;
@@ -496,7 +535,7 @@ public final class Transformer {
       boolean removeVideo,
       String containerMimeType,
       TransformationRequest transformationRequest,
-      Transformer.Listener listener,
+      ListenerSet<Transformer.Listener> listeners,
       Looper looper,
       Clock clock,
       Codec.EncoderFactory encoderFactory,
@@ -510,7 +549,7 @@ public final class Transformer {
     this.removeVideo = removeVideo;
     this.containerMimeType = containerMimeType;
     this.transformationRequest = transformationRequest;
-    this.listener = listener;
+    this.listeners = listeners;
     this.looper = looper;
     this.clock = clock;
     this.encoderFactory = encoderFactory;
@@ -525,20 +564,52 @@ public final class Transformer {
   }
 
   /**
-   * Sets the {@link Transformer.Listener} to listen to the transformation events.
+   * @deprecated Use {@link #addListener(Listener)}, {@link #removeListener(Listener)} or {@link
+   *     #removeAllListeners()} instead.
+   */
+  @Deprecated
+  public void setListener(Transformer.Listener listener) {
+    verifyApplicationThread();
+    this.listeners.clear();
+    this.listeners.add(listener);
+  }
+
+  /**
+   * Adds a {@link Transformer.Listener} to listen to the transformation events.
    *
    * @param listener A {@link Transformer.Listener}.
    * @throws IllegalStateException If this method is called from the wrong thread.
    */
-  public void setListener(Transformer.Listener listener) {
+  public void addListener(Transformer.Listener listener) {
     verifyApplicationThread();
-    this.listener = listener;
+    this.listeners.add(listener);
+  }
+
+  /**
+   * Removes a {@link Transformer.Listener}.
+   *
+   * @param listener A {@link Transformer.Listener}.
+   * @throws IllegalStateException If this method is called from the wrong thread.
+   */
+  public void removeListener(Transformer.Listener listener) {
+    verifyApplicationThread();
+    this.listeners.remove(listener);
+  }
+
+  /**
+   * Removes all {@link Transformer.Listener listeners}.
+   *
+   * @throws IllegalStateException If this method is called from the wrong thread.
+   */
+  public void removeAllListeners() {
+    verifyApplicationThread();
+    this.listeners.clear();
   }
 
   /**
    * Starts an asynchronous operation to transform the given {@link MediaItem}.
    *
-   * <p>The transformation state is notified through the {@link Builder#setListener(Listener)
+   * <p>The transformation state is notified through the {@link Builder#addListener(Listener)
    * listener}.
    *
    * <p>Concurrent transformations on the same Transformer object are not allowed.
@@ -561,7 +632,7 @@ public final class Transformer {
   /**
    * Starts an asynchronous operation to transform the given {@link MediaItem}.
    *
-   * <p>The transformation state is notified through the {@link Builder#setListener(Listener)
+   * <p>The transformation state is notified through the {@link Builder#addListener(Listener)
    * listener}.
    *
    * <p>Concurrent transformations on the same Transformer object are not allowed.
@@ -842,16 +913,26 @@ public final class Transformer {
       }
 
       if (exception == null && resourceReleaseException == null) {
-        listener.onTransformationCompleted(mediaItem);
+        // TODO(b/213341814): Add event flags for Transformer events.
+        listeners.queueEvent(
+            /* eventFlag= */ C.INDEX_UNSET,
+            listener -> listener.onTransformationCompleted(mediaItem));
+        listeners.flushEvents();
         return;
       }
 
       if (exception != null) {
-        listener.onTransformationError(mediaItem, exception);
+        listeners.queueEvent(
+            /* eventFlag= */ C.INDEX_UNSET,
+            listener -> listener.onTransformationError(mediaItem, exception));
       }
       if (resourceReleaseException != null) {
-        listener.onTransformationError(mediaItem, resourceReleaseException);
+        TransformationException finalResourceReleaseException = resourceReleaseException;
-      }
+        listeners.queueEvent(
+            /* eventFlag= */ C.INDEX_UNSET,
+            listener -> listener.onTransformationError(mediaItem, finalResourceReleaseException));
+      }
+      listeners.flushEvents();
     }
   }
 }

libraries/transformer/src/test/java/androidx/media3/transformer/TransformerTest.java

@@ -22,6 +22,9 @@ import static androidx.media3.transformer.Transformer.PROGRESS_STATE_UNAVAILABLE
 import static androidx.media3.transformer.Transformer.PROGRESS_STATE_WAITING_FOR_AVAILABILITY;
 import static com.google.common.truth.Truth.assertThat;
 import static org.junit.Assert.assertThrows;
+import static org.mockito.Mockito.mock;
+import static org.mockito.Mockito.times;
+import static org.mockito.Mockito.verify;
 
 import android.content.Context;
 import android.media.MediaCrypto;
@@ -248,6 +251,77 @@ public final class TransformerTest {
         context, testMuxer, getDumpFileName(FILE_AUDIO_VIDEO + ".novideo"));
   }
 
+  @Test
+  public void startTransformation_withMultipleListeners_callsEachOnCompletion() throws Exception {
+    Transformer.Listener mockListener1 = mock(Transformer.Listener.class);
+    Transformer.Listener mockListener2 = mock(Transformer.Listener.class);
+    Transformer.Listener mockListener3 = mock(Transformer.Listener.class);
+    Transformer transformer =
+        new Transformer.Builder(context)
+            .setClock(clock)
+            .setMuxerFactory(new TestMuxerFactory())
+            .addListener(mockListener1)
+            .addListener(mockListener2)
+            .addListener(mockListener3)
+            .build();
+    MediaItem mediaItem = MediaItem.fromUri(URI_PREFIX + FILE_AUDIO_VIDEO);
+
+    transformer.startTransformation(mediaItem, outputPath);
+    TransformerTestRunner.runUntilCompleted(transformer);
+
+    verify(mockListener1, times(1)).onTransformationCompleted(mediaItem);
+    verify(mockListener2, times(1)).onTransformationCompleted(mediaItem);
+    verify(mockListener3, times(1)).onTransformationCompleted(mediaItem);
+  }
+
+  @Test
+  public void startTransformation_withMultipleListeners_callsEachOnError() throws Exception {
+    Transformer.Listener mockListener1 = mock(Transformer.Listener.class);
+    Transformer.Listener mockListener2 = mock(Transformer.Listener.class);
+    Transformer.Listener mockListener3 = mock(Transformer.Listener.class);
+    Transformer transformer =
+        new Transformer.Builder(context)
+            .setClock(clock)
+            .setMuxerFactory(new TestMuxerFactory())
+            .addListener(mockListener1)
+            .addListener(mockListener2)
+            .addListener(mockListener3)
+            .build();
+    MediaItem mediaItem = MediaItem.fromUri(URI_PREFIX + FILE_AUDIO_UNSUPPORTED_BY_MUXER);
+
+    transformer.startTransformation(mediaItem, outputPath);
+    TransformationException exception = TransformerTestRunner.runUntilError(transformer);
+
+    verify(mockListener1, times(1)).onTransformationError(mediaItem, exception);
+    verify(mockListener2, times(1)).onTransformationError(mediaItem, exception);
+    verify(mockListener3, times(1)).onTransformationError(mediaItem, exception);
+  }
+
+  @Test
+  public void startTransformation_afterBuildUponWithListenerRemoved_onlyCallsRemainingListeners()
+      throws Exception {
+    Transformer.Listener mockListener1 = mock(Transformer.Listener.class);
+    Transformer.Listener mockListener2 = mock(Transformer.Listener.class);
+    Transformer.Listener mockListener3 = mock(Transformer.Listener.class);
+    Transformer transformer1 =
+        new Transformer.Builder(context)
+            .setClock(clock)
+            .setMuxerFactory(new TestMuxerFactory())
+            .addListener(mockListener1)
+            .addListener(mockListener2)
+            .addListener(mockListener3)
+            .build();
+    Transformer transformer2 = transformer1.buildUpon().removeListener(mockListener2).build();
+    MediaItem mediaItem = MediaItem.fromUri(URI_PREFIX + FILE_AUDIO_VIDEO);
+
+    transformer2.startTransformation(mediaItem, outputPath);
+    TransformerTestRunner.runUntilCompleted(transformer2);
+
+    verify(mockListener1, times(1)).onTransformationCompleted(mediaItem);
+    verify(mockListener2, times(0)).onTransformationCompleted(mediaItem);
+    verify(mockListener3, times(1)).onTransformationCompleted(mediaItem);
+  }
+
   @Test
   public void startTransformation_flattenForSlowMotion_completesSuccessfully() throws Exception {
     Transformer transformer =

libraries/transformer/src/test/java/androidx/media3/transformer/TransformerTestRunner.java

@@ -69,7 +69,7 @@ public final class TransformerTestRunner {
   private static TransformationException runUntilListenerCalled(Transformer transformer)
       throws TimeoutException {
     TransformationResult transformationResult = new TransformationResult();
-    Transformer.Listener listener =
+    transformer.addListener(
         new Transformer.Listener() {
           @Override
           public void onTransformationCompleted(MediaItem inputMediaItem) {
@@ -81,8 +81,7 @@ public final class TransformerTestRunner {
               MediaItem inputMediaItem, TransformationException exception) {
             transformationResult.exception = exception;
           }
-        };
+        });
-    transformer.setListener(listener);
     runLooperUntil(
         transformer.getApplicationLooper(),
         () -> transformationResult.isCompleted || transformationResult.exception != null);