Add API for injecting AudioMixer.Factory.

Rename AudioMixerImpl to DefaultAudioMixer.

Removes the AudioMixerImpl specific getOutputAudioFormat, as the caller
defines and sets this.

PiperOrigin-RevId: 555887722

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

@@ -28,17 +28,19 @@ import java.nio.ByteBuffer;
 
 /** Processes raw audio samples. */
 /* package */ final class AudioGraph {
-  private final AudioMixerImpl mixer;
+  private final AudioMixer mixer;
   private final SparseArray<AudioGraphInput> inputs;
 
+  private AudioFormat outputAudioFormat;
   private int finishedInputs;
   private ByteBuffer currentOutput;
 
   /** Creates an instance. */
-  public AudioGraph() {
-    mixer = new AudioMixerImpl(/* outputSilenceWithNoSources= */ false);
+  public AudioGraph(AudioMixer.Factory mixerFactory) {
+    mixer = mixerFactory.create();
     inputs = new SparseArray<>();
     currentOutput = EMPTY_BUFFER;
+    outputAudioFormat = AudioFormat.NOT_SET;
   }
 
   /** Returns a new {@link AudioGraphInput} instance. */
@@ -48,10 +50,9 @@ import java.nio.ByteBuffer;
       AudioGraphInput audioGraphInput = new AudioGraphInput(item, format);
 
       if (inputs.size() == 0) {
+        outputAudioFormat = audioGraphInput.getOutputAudioFormat();
         mixer.configure(
-            audioGraphInput.getOutputAudioFormat(),
-            /* bufferSizeMs= */ C.LENGTH_UNSET,
-            /* startTimeUs= */ 0);
+            outputAudioFormat, /* bufferSizeMs= */ C.LENGTH_UNSET, /* startTimeUs= */ 0);
       }
 
       int sourceId = mixer.addSource(audioGraphInput.getOutputAudioFormat(), /* startTimeUs= */ 0);
@@ -69,7 +70,7 @@ import java.nio.ByteBuffer;
    * registered}.
    */
   public AudioFormat getOutputAudioFormat() {
-    return mixer.getOutputAudioFormat();
+    return outputAudioFormat;
   }
 
   /**

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

@@ -53,9 +53,18 @@ import java.nio.ByteBuffer;
  */
 @UnstableApi
 public interface AudioMixer {
-  /** Creates an unconfigured instance. */
-  public static AudioMixer create() {
-    return new AudioMixerImpl(/* outputSilenceWithNoSources= */ true);
+
+  /** A factory for {@link AudioMixer} instances. */
+  interface Factory {
+    AudioMixer create();
+  }
+
+  /**
+   * @deprecated Use {@link DefaultAudioMixer.Factory#create()}.
+   */
+  @Deprecated
+  static AudioMixer create() {
+    return new DefaultAudioMixer.Factory(/* outputSilenceWithNoSources= */ true).create();
   }
 
   /**

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

@@ -52,12 +52,13 @@ import org.checkerframework.dataflow.qual.Pure;
       Format firstInputFormat,
       TransformationRequest transformationRequest,
       EditedMediaItem firstEditedMediaItem,
+      AudioMixer.Factory mixerFactory,
       Codec.EncoderFactory encoderFactory,
       MuxerWrapper muxerWrapper,
       FallbackListener fallbackListener)
       throws ExportException {
     super(firstAssetLoaderTrackFormat, muxerWrapper);
-    audioGraph = new AudioGraph();
+    audioGraph = new AudioGraph(mixerFactory);
     this.firstInputFormat = firstInputFormat;
     firstInput = audioGraph.registerInput(firstEditedMediaItem, firstInputFormat);
     encoderInputAudioFormat = audioGraph.getOutputAudioFormat();

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

@@ -28,12 +28,42 @@ import androidx.media3.common.audio.AudioMixingUtil;
 import androidx.media3.common.audio.AudioProcessor.AudioFormat;
 import androidx.media3.common.audio.AudioProcessor.UnhandledAudioFormatException;
 import androidx.media3.common.audio.ChannelMixingMatrix;
+import androidx.media3.common.util.UnstableApi;
 import androidx.media3.common.util.Util;
 import java.nio.ByteBuffer;
 import java.nio.ByteOrder;
 
 /** An {@link AudioMixer} that incrementally mixes source audio into a fixed size mixing buffer. */
-/* package */ final class AudioMixerImpl implements AudioMixer {
+@UnstableApi
+public final class DefaultAudioMixer implements AudioMixer {
+
+  /** An {@link AudioMixer.Factory} implementation for {@link DefaultAudioMixer} instances. */
+  public static final class Factory implements AudioMixer.Factory {
+    private final boolean outputSilenceWithNoSources;
+
+    /**
+     * Creates an instance that does not {@linkplain #getOutput() output} silence when there are no
+     * {@linkplain #addSource sources}.
+     */
+    public Factory() {
+      this(/* outputSilenceWithNoSources= */ false);
+    }
+
+    /**
+     * Creates an instance.
+     *
+     * @param outputSilenceWithNoSources Whether to {@linkplain #getOutput() output} silence when
+     *     there are no {@linkplain #addSource sources}.
+     */
+    public Factory(boolean outputSilenceWithNoSources) {
+      this.outputSilenceWithNoSources = outputSilenceWithNoSources;
+    }
+
+    @Override
+    public DefaultAudioMixer create() {
+      return new DefaultAudioMixer(outputSilenceWithNoSources);
+    }
+  }
 
   // TODO(b/290002438, b/276734854): Improve buffer management & determine best default size.
   private static final int DEFAULT_BUFFER_SIZE_MS = 500;
@@ -60,13 +90,7 @@ import java.nio.ByteOrder;
    */
   private long maxPositionOfRemovedSources;
 
-  /**
-   * Creates an instance.
-   *
-   * @param outputSilenceWithNoSources Whether {@link #getOutput()} should output buffers of silence
-   *     when there are no {@link #addSource sources}.
-   */
-  public AudioMixerImpl(boolean outputSilenceWithNoSources) {
+  private DefaultAudioMixer(boolean outputSilenceWithNoSources) {
     sources = new SparseArray<>();
     outputAudioFormat = AudioFormat.NOT_SET;
     bufferSizeFrames = C.LENGTH_UNSET;
@@ -79,10 +103,6 @@ import java.nio.ByteOrder;
     }
   }
 
-  public AudioFormat getOutputAudioFormat() {
-    return outputAudioFormat;
-  }
-
   @Override
   public void configure(AudioFormat outputAudioFormat, int bufferSizeMs, long startTimeUs)
       throws UnhandledAudioFormatException {

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

@@ -94,6 +94,7 @@ public final class Transformer {
     private boolean flattenForSlowMotion;
     private ListenerSet<Transformer.Listener> listeners;
     private AssetLoader.@MonotonicNonNull Factory assetLoaderFactory;
+    private AudioMixer.Factory audioMixerFactory;
     private VideoFrameProcessor.Factory videoFrameProcessorFactory;
     private Codec.EncoderFactory encoderFactory;
     private Muxer.Factory muxerFactory;
@@ -110,6 +111,7 @@ public final class Transformer {
       this.context = context.getApplicationContext();
       audioProcessors = ImmutableList.of();
       videoEffects = ImmutableList.of();
+      audioMixerFactory = new DefaultAudioMixer.Factory();
       videoFrameProcessorFactory = new DefaultVideoFrameProcessor.Factory.Builder().build();
       encoderFactory = new DefaultEncoderFactory.Builder(this.context).build();
       muxerFactory = new DefaultMuxer.Factory();
@@ -131,6 +133,7 @@ public final class Transformer {
       this.removeVideo = transformer.removeVideo;
       this.listeners = transformer.listeners;
       this.assetLoaderFactory = transformer.assetLoaderFactory;
+      this.audioMixerFactory = transformer.audioMixerFactory;
       this.videoFrameProcessorFactory = transformer.videoFrameProcessorFactory;
       this.encoderFactory = transformer.encoderFactory;
       this.muxerFactory = transformer.muxerFactory;
@@ -339,7 +342,23 @@ public final class Transformer {
     }
 
     /**
-     * Sets the factory to be used to create {@link VideoFrameProcessor} instances.
+     * Sets the {@link AudioMixer.Factory} to be used when {@linkplain AudioMixer audio mixing} is
+     * needed.
+     *
+     * <p>The default value is a {@link DefaultAudioMixer.Factory} with default values.
+     *
+     * @param audioMixerFactory A {@link AudioMixer.Factory}.
+     * @return This builder.
+     */
+    @CanIgnoreReturnValue
+    public Builder setAudioMixerFactory(AudioMixer.Factory audioMixerFactory) {
+      this.audioMixerFactory = audioMixerFactory;
+      return this;
+    }
+
+    /**
+     * Sets the {@link VideoFrameProcessor.Factory} to be used to create {@link VideoFrameProcessor}
+     * instances.
      *
      * <p>The default value is a {@link DefaultVideoFrameProcessor.Factory} built with default
      * values.
@@ -369,7 +388,7 @@ public final class Transformer {
     }
 
     /**
-     * Sets the factory for muxers that write the media container.
+     * Sets the {@link Muxer.Factory} for muxers that write the media container.
      *
      * <p>The default value is a {@link DefaultMuxer.Factory}.
      *
@@ -468,6 +487,7 @@ public final class Transformer {
           flattenForSlowMotion,
           listeners,
           assetLoaderFactory,
+          audioMixerFactory,
           videoFrameProcessorFactory,
           encoderFactory,
           muxerFactory,
@@ -637,6 +657,7 @@ public final class Transformer {
   private final boolean flattenForSlowMotion;
   private final ListenerSet<Transformer.Listener> listeners;
   @Nullable private final AssetLoader.Factory assetLoaderFactory;
+  private final AudioMixer.Factory audioMixerFactory;
   private final VideoFrameProcessor.Factory videoFrameProcessorFactory;
   private final Codec.EncoderFactory encoderFactory;
   private final Muxer.Factory muxerFactory;
@@ -656,6 +677,7 @@ public final class Transformer {
       boolean flattenForSlowMotion,
       ListenerSet<Listener> listeners,
       @Nullable AssetLoader.Factory assetLoaderFactory,
+      AudioMixer.Factory audioMixerFactory,
       VideoFrameProcessor.Factory videoFrameProcessorFactory,
       Codec.EncoderFactory encoderFactory,
       Muxer.Factory muxerFactory,
@@ -672,6 +694,7 @@ public final class Transformer {
     this.flattenForSlowMotion = flattenForSlowMotion;
     this.listeners = listeners;
     this.assetLoaderFactory = assetLoaderFactory;
+    this.audioMixerFactory = audioMixerFactory;
     this.videoFrameProcessorFactory = videoFrameProcessorFactory;
     this.encoderFactory = encoderFactory;
     this.muxerFactory = muxerFactory;
@@ -839,6 +862,7 @@ public final class Transformer {
             path,
             transformationRequest,
             assetLoaderFactory,
+            audioMixerFactory,
             videoFrameProcessorFactory,
             encoderFactory,
             muxerFactory,

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

@@ -136,6 +136,7 @@ import org.checkerframework.checker.nullness.qual.MonotonicNonNull;
       String outputPath,
       TransformationRequest transformationRequest,
       AssetLoader.Factory assetLoaderFactory,
+      AudioMixer.Factory audioMixerFactory,
       VideoFrameProcessor.Factory videoFrameProcessorFactory,
       Codec.EncoderFactory encoderFactory,
       Muxer.Factory muxerFactory,
@@ -162,6 +163,7 @@ import org.checkerframework.checker.nullness.qual.MonotonicNonNull;
               /* sequenceIndex= */ i,
               composition,
               transformationRequest,
+              audioMixerFactory,
               videoFrameProcessorFactory,
               fallbackListener,
               debugViewProvider);
@@ -449,6 +451,7 @@ import org.checkerframework.checker.nullness.qual.MonotonicNonNull;
     private final ImmutableList<EditedMediaItem> editedMediaItems;
     private final Composition composition;
     private final TransformationRequest transformationRequest;
+    private final AudioMixer.Factory audioMixerFactory;
     private final VideoFrameProcessor.Factory videoFrameProcessorFactory;
     private final FallbackListener fallbackListener;
     private final DebugViewProvider debugViewProvider;
@@ -458,6 +461,7 @@ import org.checkerframework.checker.nullness.qual.MonotonicNonNull;
         int sequenceIndex,
         Composition composition,
         TransformationRequest transformationRequest,
+        AudioMixer.Factory audioMixerFactory,
         VideoFrameProcessor.Factory videoFrameProcessorFactory,
         FallbackListener fallbackListener,
         DebugViewProvider debugViewProvider) {
@@ -465,6 +469,7 @@ import org.checkerframework.checker.nullness.qual.MonotonicNonNull;
       this.editedMediaItems = composition.sequences.get(sequenceIndex).editedMediaItems;
       this.composition = composition;
       this.transformationRequest = transformationRequest;
+      this.audioMixerFactory = audioMixerFactory;
       this.videoFrameProcessorFactory = videoFrameProcessorFactory;
       this.fallbackListener = fallbackListener;
       this.debugViewProvider = debugViewProvider;
@@ -579,6 +584,7 @@ import org.checkerframework.checker.nullness.qual.MonotonicNonNull;
                 /* firstInputFormat= */ assetLoaderOutputFormat,
                 transformationRequest,
                 editedMediaItems.get(0),
+                audioMixerFactory,
                 encoderFactory,
                 muxerWrapper,
                 fallbackListener));

libraries/transformer/src/test/java/androidx/media3/transformer/DefaultAudioMixerTest.java

@@ -33,7 +33,7 @@ import org.robolectric.ParameterizedRobolectricTestRunner.Parameter;
 import org.robolectric.ParameterizedRobolectricTestRunner.Parameters;
 
 /**
- * Unit tests for {@link AudioMixerImpl}.
+ * Unit tests for {@link DefaultAudioMixer}.
  *
  * <p>The duration of a given buffer can be calculated with the {@link AudioFormat}:
  *
@@ -48,7 +48,7 @@ import org.robolectric.ParameterizedRobolectricTestRunner.Parameters;
  */
 // TODO(b/290002720): Expand and generalize parameterized test cases.
 @RunWith(ParameterizedRobolectricTestRunner.class)
-public final class AudioMixerImplTest {
+public final class DefaultAudioMixerTest {
 
   @Parameters(name = "outputSilenceWithNoSources={0}")
   public static ImmutableList<Boolean> parameters() {
@@ -67,7 +67,7 @@ public final class AudioMixerImplTest {
 
   @Before
   public void setup() {
-    mixer = new AudioMixerImpl(outputSilenceWithNoSources);
+    mixer = new DefaultAudioMixer.Factory(outputSilenceWithNoSources).create();
   }
 
   @Test