Change FallbackListener registerTrack to setTrackCount

AssetLoader declares the tracks with a setTrackCount() method. Setting
the track count on the FallbackListener is easier than calling
registerTrack() as many times as the number of tracks.

PiperOrigin-RevId: 496919969

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

@@ -18,6 +18,7 @@ package com.google.android.exoplayer2.transformer;
 
 import static com.google.android.exoplayer2.util.Assertions.checkState;
 
+import androidx.annotation.IntRange;
 import com.google.android.exoplayer2.C;
 import com.google.android.exoplayer2.MediaItem;
 import com.google.android.exoplayer2.util.HandlerWrapper;
@@ -61,13 +62,13 @@ import com.google.android.exoplayer2.util.Util;
   }
 
   /**
-   * Registers an output track.
+   * Sets the number of output tracks.
    *
-   * <p>All tracks must be registered before a transformation request is {@linkplain
+   * <p>The track count must be set before a transformation request is {@linkplain
    * #onTransformationRequestFinalized(TransformationRequest) finalized}.
    */
-  public void registerTrack() {
-    trackCount++;
+  public void setTrackCount(@IntRange(from = 1) int trackCount) {
+    this.trackCount = trackCount;
   }
 
   /**
@@ -82,8 +83,8 @@ import com.google.android.exoplayer2.util.Util;
    * TransformationRequest)} once this method has been called for each track.
    *
    * @param transformationRequest The final {@link TransformationRequest} for a track.
-   * @throws IllegalStateException If called for more tracks than registered using {@link
-   *     #registerTrack()}.
+   * @throws IllegalStateException If called for more tracks than declared in {@link
+   *     #setTrackCount(int)}.
    */
   public void onTransformationRequestFinalized(TransformationRequest transformationRequest) {
     checkState(trackCount-- > 0);

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

@@ -417,8 +417,8 @@ import org.checkerframework.checker.nullness.qual.MonotonicNonNull;
         }
         for (int i = 0; i < trackCount.get(); i++) {
           muxerWrapper.registerTrack();
-          fallbackListener.registerTrack();
         }
+        fallbackListener.setTrackCount(trackCount.get());
       }
 
       SamplePipeline samplePipeline =

library/transformer/src/test/java/com/google/android/exoplayer2/transformer/FallbackListenerTest.java

@@ -40,7 +40,7 @@ public class FallbackListenerTest {
   private static final MediaItem PLACEHOLDER_MEDIA_ITEM = MediaItem.fromUri(Uri.EMPTY);
 
   @Test
-  public void onTransformationRequestFinalized_withoutTrackRegistration_throwsException() {
+  public void onTransformationRequestFinalized_withoutTrackCountSet_throwsException() {
     TransformationRequest transformationRequest = new TransformationRequest.Builder().build();
     FallbackListener fallbackListener =
         new FallbackListener(
@@ -52,13 +52,13 @@ public class FallbackListenerTest {
   }
 
   @Test
-  public void onTransformationRequestFinalized_afterTrackRegistration_completesSuccessfully() {
+  public void onTransformationRequestFinalized_afterTrackCountSet_completesSuccessfully() {
     TransformationRequest transformationRequest = new TransformationRequest.Builder().build();
     FallbackListener fallbackListener =
         new FallbackListener(
             PLACEHOLDER_MEDIA_ITEM, createListenerSet(), createHandler(), transformationRequest);
 
-    fallbackListener.registerTrack();
+    fallbackListener.setTrackCount(1);
     fallbackListener.onTransformationRequestFinalized(transformationRequest);
     ShadowLooper.idleMainLooper();
   }
@@ -76,7 +76,7 @@ public class FallbackListenerTest {
             createHandler(),
             originalRequest);
 
-    fallbackListener.registerTrack();
+    fallbackListener.setTrackCount(1);
     fallbackListener.onTransformationRequestFinalized(unchangedRequest);
     ShadowLooper.idleMainLooper();
 
@@ -97,7 +97,7 @@ public class FallbackListenerTest {
             createHandler(),
             originalRequest);
 
-    fallbackListener.registerTrack();
+    fallbackListener.setTrackCount(1);
     fallbackListener.onTransformationRequestFinalized(audioFallbackRequest);
     ShadowLooper.idleMainLooper();
 
@@ -127,8 +127,7 @@ public class FallbackListenerTest {
             createHandler(),
             originalRequest);
 
-    fallbackListener.registerTrack();
-    fallbackListener.registerTrack();
+    fallbackListener.setTrackCount(2);
     fallbackListener.onTransformationRequestFinalized(audioFallbackRequest);
     fallbackListener.onTransformationRequestFinalized(videoFallbackRequest);
     ShadowLooper.idleMainLooper();

library/transformer/src/test/java/com/google/android/exoplayer2/transformer/VideoEncoderWrapperTest.java

@@ -61,8 +61,8 @@ public final class VideoEncoderWrapperTest {
           fallbackListener);
 
   @Before
-  public void registerTrack() {
-    fallbackListener.registerTrack();
+  public void setUp() {
+    fallbackListener.setTrackCount(1);
     createShadowH264Encoder();
   }