Add IntRange annotation to onTrackCount

PiperOrigin-RevId: 496942702

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

@@ -18,6 +18,7 @@ package androidx.media3.transformer;
 
 import android.content.Context;
 import android.os.Looper;
+import androidx.annotation.IntRange;
 import androidx.media3.common.Format;
 import androidx.media3.common.MediaItem;
 import androidx.media3.common.util.Clock;
@@ -131,7 +132,7 @@ public interface AssetLoader {
     void onDurationUs(long durationUs);
 
     /** Called when the number of tracks output by the asset loader is known. */
-    void onTrackCount(int trackCount);
+    void onTrackCount(@IntRange(from = 1) int trackCount);
 
     /**
      * Called when the information on a track is known.

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

@@ -16,6 +16,7 @@
 
 package androidx.media3.transformer;
 
+import static androidx.media3.common.PlaybackException.ERROR_CODE_FAILED_RUNTIME_CHECK;
 import static androidx.media3.common.util.Assertions.checkStateNotNull;
 import static androidx.media3.exoplayer.DefaultLoadControl.DEFAULT_BUFFER_FOR_PLAYBACK_AFTER_REBUFFER_MS;
 import static androidx.media3.exoplayer.DefaultLoadControl.DEFAULT_BUFFER_FOR_PLAYBACK_MS;
@@ -350,7 +351,15 @@ public final class ExoPlayerAssetLoader implements AssetLoader {
       if (tracks.isTypeSelected(C.TRACK_TYPE_VIDEO)) {
         trackCount++;
       }
-      assetLoaderListener.onTrackCount(trackCount);
+      if (trackCount == 0) {
+        assetLoaderListener.onError(
+            new PlaybackException(
+                "The asset loader has no track to output.",
+                /* cause= */ null,
+                ERROR_CODE_FAILED_RUNTIME_CHECK));
+      } else {
+        assetLoaderListener.onTrackCount(trackCount);
+      }
     }
 
     @Override

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

@@ -401,8 +401,9 @@ import org.checkerframework.checker.nullness.qual.MonotonicNonNull;
 
     @Override
     public void onTrackCount(int trackCount) {
-      if (trackCount == 0) {
-        onError(new IllegalStateException("The output does not contain any tracks."));
+      if (trackCount <= 0) {
+        onError(new IllegalStateException("AssetLoader instances must provide at least 1 track."));
+        return;
       }
       this.trackCount.set(trackCount);
       if (forceSilentAudio) {