Handle multiple sequences in a Composition

This lays the groundwork for full multi-asset, and more particularly for
adding looping background audio.

PiperOrigin-RevId: 512887888

library/transformer/src/main/java/com/google/android/exoplayer2/transformer/CompositeAssetLoader.java

@@ -73,6 +73,7 @@ import java.util.concurrent.atomic.AtomicInteger;
   private final AtomicInteger nonEndedTracks;
 
   private AssetLoader currentAssetLoader;
+  private boolean trackCountReported;
   private int processedInputsSize;
 
   private volatile long currentDurationUs;
@@ -197,8 +198,11 @@ import java.util.concurrent.atomic.AtomicInteger;
     if (currentMediaItemIndex.get() == 0) {
       boolean addForcedAudioTrack =
           forceAudioTrack && nonEndedTracks.get() == 1 && trackType == C.TRACK_TYPE_VIDEO;
-      int trackCount = nonEndedTracks.get() + (addForcedAudioTrack ? 1 : 0);
-      compositeAssetLoaderListener.onTrackCount(trackCount);
+      if (!trackCountReported) {
+        int trackCount = nonEndedTracks.get() + (addForcedAudioTrack ? 1 : 0);
+        compositeAssetLoaderListener.onTrackCount(trackCount);
+        trackCountReported = true;
+      }
       sampleConsumer =
           new SampleConsumerWrapper(
               compositeAssetLoaderListener.onTrackAdded(

library/transformer/src/main/java/com/google/android/exoplayer2/transformer/FallbackListener.java

@@ -23,6 +23,7 @@ import com.google.android.exoplayer2.C;
 import com.google.android.exoplayer2.util.HandlerWrapper;
 import com.google.android.exoplayer2.util.ListenerSet;
 import com.google.android.exoplayer2.util.Util;
+import java.util.concurrent.atomic.AtomicInteger;
 
 /**
  * Listener for fallback {@link TransformationRequest TransformationRequests} from the audio and
@@ -31,12 +32,12 @@ import com.google.android.exoplayer2.util.Util;
 /* package */ final class FallbackListener {
 
   private final Composition composition;
-  private final TransformationRequest originalTransformationRequest;
   private final ListenerSet<Transformer.Listener> transformerListeners;
   private final HandlerWrapper transformerListenerHandler;
+  private final TransformationRequest originalTransformationRequest;
+  private final AtomicInteger trackCount;
 
   private TransformationRequest fallbackTransformationRequest;
-  private int trackCount;
 
   /**
    * Creates a new instance.
@@ -58,6 +59,7 @@ import com.google.android.exoplayer2.util.Util;
     this.transformerListenerHandler = transformerListenerHandler;
     this.originalTransformationRequest = originalTransformationRequest;
     this.fallbackTransformationRequest = originalTransformationRequest;
+    trackCount = new AtomicInteger();
   }
 
   /**
@@ -65,9 +67,11 @@ import com.google.android.exoplayer2.util.Util;
    *
    * <p>The track count must be set before a transformation request is {@linkplain
    * #onTransformationRequestFinalized(TransformationRequest) finalized}.
+   *
+   * <p>Can be called from any thread.
    */
   public void setTrackCount(@IntRange(from = 1) int trackCount) {
-    this.trackCount = trackCount;
+    this.trackCount.set(trackCount);
   }
 
   /**
@@ -86,7 +90,7 @@ import com.google.android.exoplayer2.util.Util;
    *     #setTrackCount(int)}.
    */
   public void onTransformationRequestFinalized(TransformationRequest transformationRequest) {
-    checkState(trackCount-- > 0);
+    checkState(trackCount.getAndDecrement() > 0);
 
     TransformationRequest.Builder fallbackRequestBuilder =
         fallbackTransformationRequest.buildUpon();
@@ -107,7 +111,8 @@ import com.google.android.exoplayer2.util.Util;
     TransformationRequest newFallbackTransformationRequest = fallbackRequestBuilder.build();
     fallbackTransformationRequest = newFallbackTransformationRequest;
 
-    if (trackCount == 0 && !originalTransformationRequest.equals(fallbackTransformationRequest)) {
+    if (trackCount.get() == 0
+        && !originalTransformationRequest.equals(fallbackTransformationRequest)) {
       transformerListenerHandler.post(
           () ->
               transformerListeners.sendEvent(

library/transformer/src/main/java/com/google/android/exoplayer2/transformer/MuxerWrapper.java

@@ -69,7 +69,6 @@ import org.checkerframework.checker.nullness.qual.RequiresNonNull;
   private final SparseArray<TrackInfo> trackTypeToInfo;
   private final ScheduledExecutorService abortScheduledExecutorService;
 
-  private int trackCount;
   private boolean isReady;
   private boolean isEnded;
   private @C.TrackType int previousTrackType;
@@ -79,6 +78,8 @@ import org.checkerframework.checker.nullness.qual.RequiresNonNull;
   private boolean isAborted;
   private @MonotonicNonNull Muxer muxer;
 
+  private volatile int trackCount;
+
   public MuxerWrapper(String outputPath, Muxer.Factory muxerFactory, Listener listener) {
     this.outputPath = outputPath;
     this.muxerFactory = muxerFactory;
@@ -95,6 +96,8 @@ import org.checkerframework.checker.nullness.qual.RequiresNonNull;
    * <p>The track count must be set before any track format is {@linkplain #addTrackFormat(Format)
    * added}.
    *
+   * <p>Can be called from any thread.
+   *
    * @throws IllegalStateException If a track format was {@linkplain #addTrackFormat(Format) added}
    *     before calling this method.
    */
@@ -135,6 +138,7 @@ import org.checkerframework.checker.nullness.qual.RequiresNonNull;
    *     the track.
    */
   public void addTrackFormat(Format format) throws Muxer.MuxerException {
+    int trackCount = this.trackCount;
     checkState(trackCount > 0, "The track count should be set before the formats are added.");
     checkState(trackTypeToInfo.size() < trackCount, "All track formats have already been added.");
     @Nullable String sampleMimeType = format.sampleMimeType;

library/transformer/src/main/java/com/google/android/exoplayer2/transformer/SamplePipeline.java

@@ -39,8 +39,9 @@ import java.util.List;
  *
  * <p>The {@link SampleConsumer} and {@link OnMediaItemChangedListener} methods must be called from
  * the same thread. This thread can change when the {@link
- * OnMediaItemChangedListener#onMediaItemChanged(EditedMediaItem, Format, long) MediaItem} changes,
- * and can be different from the thread used to call the other {@code SamplePipeline} methods.
+ * OnMediaItemChangedListener#onMediaItemChanged(EditedMediaItem, long, Format, boolean) MediaItem}
+ * changes, and can be different from the thread used to call the other {@code SamplePipeline}
+ * methods.
  */
 /* package */ abstract class SamplePipeline implements SampleConsumer, OnMediaItemChangedListener {