Misc small fixes

- Improve AssetLoader Javadoc
- Fix Javadoc of sample pipelines
- Improve Javadoc of Transformer.startTransformation
- Move thread hops for Transformer listener callbacks to
  TransformerInternal

PiperOrigin-RevId: 499156604

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

@@ -123,14 +123,6 @@ public interface AssetLoader {
   /**
    * A listener of {@link AssetLoader} events.
    *
-   * <p>This listener is typically used in the following way:
-   *
-   * <ul>
-   *   <li>{@linkplain #onDurationUs(long)} Report} the duration of the input media.
-   *   <li>{@linkplain #onTrackCount(int) Report} the number of output tracks.
-   *   <li>{@linkplain #onTrackAdded(Format, int, long, long) Add} the information for each track.
-   * </ul>
-   *
    * <p>This listener can be called from any thread.
    */
   interface Listener {

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

@@ -35,9 +35,7 @@ import java.util.List;
 import org.checkerframework.checker.nullness.qual.EnsuresNonNullIf;
 import org.checkerframework.dataflow.qual.Pure;
 
-/**
+/** Pipeline to apply audio processing to raw audio samples, encode them and mux them. */
- * Pipeline to decode audio samples, apply audio processing to the raw samples, and re-encode them.
- */
 /* package */ final class AudioTranscodingSamplePipeline extends BaseSamplePipeline {
 
   private static final int DEFAULT_ENCODER_BITRATE = 128 * 1024;

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

@@ -248,7 +248,7 @@ import org.checkerframework.checker.nullness.qual.RequiresNonNull;
   }
 
   /**
-   * Attempts to read input data and pass the input data to the sample pipeline.
+   * Attempts to read input data and pass it to the sample pipeline.
    *
    * @return Whether it may be possible to read more data immediately by calling this method again.
    */

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

@@ -20,7 +20,7 @@ import androidx.annotation.Nullable;
 import androidx.media3.common.Format;
 import androidx.media3.decoder.DecoderInputBuffer;
 
-/** Pipeline that passes through the samples without any re-encoding or transformation. */
+/** Pipeline that muxes encoded samples without any transcoding or transformation. */
 /* package */ final class PassthroughSamplePipeline extends BaseSamplePipeline {
 
   private final DecoderInputBuffer buffer;

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

@@ -21,7 +21,7 @@ import androidx.media3.common.util.UnstableApi;
 import androidx.media3.decoder.DecoderInputBuffer;
 
 /**
- * Pipeline for processing {@link DecoderInputBuffer DecoderInputBuffers}.
+ * Pipeline for processing media data.
  *
  * <p>This pipeline can be used to implement transformations of audio or video samples.
  */

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

@@ -43,7 +43,6 @@ import androidx.media3.effect.GlEffect;
 import androidx.media3.effect.GlEffectsFrameProcessor;
 import androidx.media3.effect.GlMatrixTransformation;
 import androidx.media3.exoplayer.audio.SonicAudioProcessor;
-import androidx.media3.exoplayer.source.MediaSource;
 import com.google.common.collect.ImmutableList;
 import com.google.errorprone.annotations.CanIgnoreReturnValue;
 import java.lang.annotation.Documented;
@@ -695,8 +694,10 @@ public final class Transformer {
    *
    * <p>Concurrent transformations on the same Transformer object are not allowed.
    *
-   * <p>The output is an MP4 file. It can contain at most one video track and one audio track. Other
+   * <p>If no custom {@link Muxer.Factory} is specified, the output is an MP4 file.
-   * track types are ignored. For adaptive bitrate {@linkplain MediaSource media sources}, the
+   *
+   * <p>The output can contain at most one video track and one audio track. Other track types are
+   * ignored. For adaptive bitrate, if no custom {@link AssetLoader.Factory} is specified, the
    * highest bitrate video and audio streams are selected.
    *
    * @param mediaItem The {@link MediaItem} to transform.
@@ -718,8 +719,10 @@ public final class Transformer {
    *
    * <p>Concurrent transformations on the same Transformer object are not allowed.
    *
-   * <p>The output is an MP4 file. It can contain at most one video track and one audio track. Other
+   * <p>If no custom {@link Muxer.Factory} is specified, the output is an MP4 file.
-   * track types are ignored. For adaptive bitrate {@linkplain MediaSource media sources}, the
+   *
+   * <p>The output can contain at most one video track and one audio track. Other track types are
+   * ignored. For adaptive bitrate, if no custom {@link AssetLoader.Factory} is specified, the
    * highest bitrate video and audio streams are selected.
    *
    * @param mediaItem The {@link MediaItem} to transform.
@@ -753,12 +756,9 @@ public final class Transformer {
     }
     TransformerInternalListener transformerInternalListener =
         new TransformerInternalListener(mediaItem);
+    HandlerWrapper applicationHandler = clock.createHandler(looper, /* callback= */ null);
     FallbackListener fallbackListener =
-        new FallbackListener(
+        new FallbackListener(mediaItem, listeners, applicationHandler, transformationRequest);
-            mediaItem,
-            listeners,
-            clock.createHandler(looper, /* callback= */ null),
-            transformationRequest);
     transformerInternal =
         new TransformerInternal(
             context,
@@ -778,6 +778,7 @@ public final class Transformer {
             muxerFactory,
             transformerInternalListener,
             fallbackListener,
+            applicationHandler,
             debugViewProvider,
             clock);
     transformerInternal.start();
@@ -836,37 +837,29 @@ public final class Transformer {
   private final class TransformerInternalListener implements TransformerInternal.Listener {
 
     private final MediaItem mediaItem;
-    private final HandlerWrapper handler;
 
     public TransformerInternalListener(MediaItem mediaItem) {
       this.mediaItem = mediaItem;
-      handler = clock.createHandler(looper, /* callback= */ null);
     }
 
     @Override
     public void onTransformationCompleted(TransformationResult transformationResult) {
       // TODO(b/213341814): Add event flags for Transformer events.
-      handler.post(
+      transformerInternal = null;
-          () -> {
+      listeners.queueEvent(
-            transformerInternal = null;
+          /* eventFlag= */ C.INDEX_UNSET,
-            listeners.queueEvent(
+          listener -> listener.onTransformationCompleted(mediaItem, transformationResult));
-                /* eventFlag= */ C.INDEX_UNSET,
+      listeners.flushEvents();
-                listener -> listener.onTransformationCompleted(mediaItem, transformationResult));
-            listeners.flushEvents();
-          });
     }
 
     @Override
     public void onTransformationError(
         TransformationResult result, TransformationException exception) {
-      handler.post(
+      transformerInternal = null;
-          () -> {
+      listeners.queueEvent(
-            transformerInternal = null;
+          /* eventFlag= */ C.INDEX_UNSET,
-            listeners.queueEvent(
+          listener -> listener.onTransformationError(mediaItem, result, exception));
-                /* eventFlag= */ C.INDEX_UNSET,
+      listeners.flushEvents();
-                listener -> listener.onTransformationError(mediaItem, result, exception));
-            listeners.flushEvents();
-          });
     }
   }
 }

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

@@ -100,6 +100,7 @@ import org.checkerframework.checker.nullness.qual.MonotonicNonNull;
   private final CapturingEncoderFactory encoderFactory;
   private final FrameProcessor.Factory frameProcessorFactory;
   private final Listener listener;
+  private final HandlerWrapper applicationHandler;
   private final DebugViewProvider debugViewProvider;
   private final Clock clock;
   private final HandlerThread internalHandlerThread;
@@ -137,6 +138,7 @@ import org.checkerframework.checker.nullness.qual.MonotonicNonNull;
       Muxer.Factory muxerFactory,
       Listener listener,
       FallbackListener fallbackListener,
+      HandlerWrapper applicationHandler,
       DebugViewProvider debugViewProvider,
       Clock clock) {
     this.context = context;
@@ -148,6 +150,7 @@ import org.checkerframework.checker.nullness.qual.MonotonicNonNull;
     this.encoderFactory = new CapturingEncoderFactory(encoderFactory);
     this.frameProcessorFactory = frameProcessorFactory;
     this.listener = listener;
+    this.applicationHandler = applicationHandler;
     this.debugViewProvider = debugViewProvider;
     this.clock = clock;
     internalHandlerThread = new HandlerThread("Transformer:Internal");
@@ -349,10 +352,15 @@ import org.checkerframework.checker.nullness.qual.MonotonicNonNull;
     }
 
     if (exception != null) {
-      listener.onTransformationError(
+      TransformationException finalException = exception;
-          transformationResultBuilder.setTransformationException(exception).build(), exception);
+      applicationHandler.post(
+          () ->
+              listener.onTransformationError(
+                  transformationResultBuilder.setTransformationException(finalException).build(),
+                  finalException));
     } else {
-      listener.onTransformationCompleted(transformationResultBuilder.build());
+      applicationHandler.post(
+          () -> listener.onTransformationCompleted(transformationResultBuilder.build()));
     }
   }