Simplify AssetLoader.Listener interface

Replace onTrackRegistered and onAllTracksRegistered with onTrackCount.

PiperOrigin-RevId: 496853037

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

@@ -119,8 +119,7 @@ public interface AssetLoader {
    *
    * <ul>
    *   <li>{@linkplain #onDurationUs(long)} Report} the duration of the input media.
-   *   <li>{@linkplain #onTrackRegistered() Register} each output track.
+   *   <li>{@linkplain #onTrackCount(int) Report} the number of output tracks.
-   *   <li>{@linkplain #onAllTracksRegistered() Signal} that all the tracks have been registered.
    *   <li>{@linkplain #onTrackAdded(Format, long, long) Add} the information for each track.
    * </ul>
    *
@@ -131,25 +130,16 @@ public interface AssetLoader {
     /** Called when the duration of the input media is known. */
     void onDurationUs(long durationUs);
 
-    /**
+    /** Called when the number of tracks output by the asset loader is known. */
-     * Called to register a single output track of sample data.
+    void onTrackCount(int trackCount);
-     *
-     * <p>Must be called for each track that will be output.
-     *
-     * <p>Must be called on the same thread as {@link #onTrackAdded(Format, long, long)}.
-     */
-    void onTrackRegistered();
-
-    /** Called when all the tracks have been {@linkplain #onTrackRegistered() registered}. */
-    void onAllTracksRegistered();
 
     /**
-     * Called when the information on a {@linkplain #onTrackRegistered() registered} track is known.
+     * Called when the information on a track is known.
      *
-     * <p>Must be called after the duration has been {@linkplain #onDurationUs(long) reported} and
+     * <p>Must be called after the {@linkplain #onDurationUs(long) duration} and the {@linkplain
-     * all the tracks have been {@linkplain #onAllTracksRegistered registered}.
+     * #onTrackCount(int) track count} have been reported.
      *
-     * <p>Must be called on the same thread as {@link #onTrackRegistered()}.
+     * <p>Must be called once per {@linkplain #onTrackCount(int) declared} track.
      *
      * @param format The {@link Format} of the input media (prior to video slow motion flattening or
      *     to decoding).

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

@@ -343,7 +343,14 @@ public final class ExoPlayerAssetLoader implements AssetLoader {
 
     @Override
     public void onTracksChanged(Tracks tracks) {
-      assetLoaderListener.onAllTracksRegistered();
+      int trackCount = 0;
+      if (tracks.isTypeSelected(C.TRACK_TYPE_AUDIO)) {
+        trackCount++;
+      }
+      if (tracks.isTypeSelected(C.TRACK_TYPE_VIDEO)) {
+        trackCount++;
+      }
+      assetLoaderListener.onTrackCount(trackCount);
     }
 
     @Override

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

@@ -129,7 +129,6 @@ import org.checkerframework.checker.nullness.qual.RequiresNonNull;
 
   @Override
   protected void onEnabled(boolean joining, boolean mayRenderStartOfStream) {
-    assetLoaderListener.onTrackRegistered();
     mediaClock.updateTimeForTrackType(getTrackType(), 0L);
   }
 

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

@@ -49,6 +49,7 @@ import java.lang.annotation.RetentionPolicy;
 import java.lang.annotation.Target;
 import java.util.ArrayList;
 import java.util.List;
+import java.util.concurrent.atomic.AtomicInteger;
 import org.checkerframework.checker.nullness.qual.MonotonicNonNull;
 
 /* package */ final class TransformerInternal {
@@ -378,15 +379,16 @@ import org.checkerframework.checker.nullness.qual.MonotonicNonNull;
 
     private final MediaItem mediaItem;
     private final FallbackListener fallbackListener;
+    private final AtomicInteger trackCount;
 
     private int tracksAddedCount;
 
     private volatile long durationUs;
-    private volatile boolean trackRegistered;
 
     public ComponentListener(MediaItem mediaItem, FallbackListener fallbackListener) {
       this.mediaItem = mediaItem;
       this.fallbackListener = fallbackListener;
+      trackCount = new AtomicInteger();
       durationUs = C.TIME_UNSET;
     }
 
@@ -398,28 +400,27 @@ import org.checkerframework.checker.nullness.qual.MonotonicNonNull;
     }
 
     @Override
-    public void onTrackRegistered() {
+    public void onTrackCount(int trackCount) {
-      trackRegistered = true;
+      if (trackCount == 0) {
-      muxerWrapper.registerTrack();
-      fallbackListener.registerTrack();
-
-      if (forceSilentAudio) {
-        muxerWrapper.registerTrack();
-        fallbackListener.registerTrack();
-      }
-    }
-
-    @Override
-    public void onAllTracksRegistered() {
-      if (!trackRegistered) {
         onError(new IllegalStateException("The output does not contain any tracks."));
       }
+      this.trackCount.set(trackCount);
     }
 
     @Override
     public SamplePipeline.Input onTrackAdded(
         Format format, long streamStartPositionUs, long streamOffsetUs)
         throws TransformationException {
+      if (tracksAddedCount == 0) {
+        if (forceSilentAudio) {
+          trackCount.incrementAndGet();
+        }
+        for (int i = 0; i < trackCount.get(); i++) {
+          muxerWrapper.registerTrack();
+          fallbackListener.registerTrack();
+        }
+      }
+
       SamplePipeline samplePipeline =
           getSamplePipeline(format, streamStartPositionUs, streamOffsetUs);
       internalHandler.obtainMessage(MSG_REGISTER_SAMPLE_PIPELINE, samplePipeline).sendToTarget();