diff --git a/libraries/transformer/src/main/java/androidx/media3/transformer/FallbackListener.java b/libraries/transformer/src/main/java/androidx/media3/transformer/FallbackListener.java
index e2fa2ee3fa..1748d97fa8 100644
--- a/libraries/transformer/src/main/java/androidx/media3/transformer/FallbackListener.java
+++ b/libraries/transformer/src/main/java/androidx/media3/transformer/FallbackListener.java
@@ -18,6 +18,7 @@ package androidx.media3.transformer;
 
 import static androidx.media3.common.util.Assertions.checkState;
 
+import androidx.annotation.IntRange;
 import androidx.media3.common.C;
 import androidx.media3.common.MediaItem;
 import androidx.media3.common.util.HandlerWrapper;
@@ -61,13 +62,13 @@ import androidx.media3.common.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 androidx.media3.common.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);
diff --git a/libraries/transformer/src/main/java/androidx/media3/transformer/TransformerInternal.java b/libraries/transformer/src/main/java/androidx/media3/transformer/TransformerInternal.java
index 97ba06bfb2..28bb0219c0 100644
--- a/libraries/transformer/src/main/java/androidx/media3/transformer/TransformerInternal.java
+++ b/libraries/transformer/src/main/java/androidx/media3/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 =
diff --git a/libraries/transformer/src/test/java/androidx/media3/transformer/FallbackListenerTest.java b/libraries/transformer/src/test/java/androidx/media3/transformer/FallbackListenerTest.java
index d0b0e4c0f3..dfee2bfa6d 100644
--- a/libraries/transformer/src/test/java/androidx/media3/transformer/FallbackListenerTest.java
+++ b/libraries/transformer/src/test/java/androidx/media3/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();
diff --git a/libraries/transformer/src/test/java/androidx/media3/transformer/VideoEncoderWrapperTest.java b/libraries/transformer/src/test/java/androidx/media3/transformer/VideoEncoderWrapperTest.java
index 3724b5691b..b227f6fe23 100644
--- a/libraries/transformer/src/test/java/androidx/media3/transformer/VideoEncoderWrapperTest.java
+++ b/libraries/transformer/src/test/java/androidx/media3/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();
   }