Add ForwardingTrackOutput implementation

This allows users to extend and customize specific methods of the `TrackOutput` implementation while inheriting default behaviors for others.

PiperOrigin-RevId: 686454360

libraries/extractor/src/main/java/androidx/media3/extractor/ForwardingTrackOutput.java

@@ -0,0 +1,75 @@
+/*
+ * Copyright 2024 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package androidx.media3.extractor;
+
+import androidx.annotation.Nullable;
+import androidx.media3.common.C;
+import androidx.media3.common.DataReader;
+import androidx.media3.common.Format;
+import androidx.media3.common.util.ParsableByteArray;
+import androidx.media3.common.util.UnstableApi;
+import java.io.IOException;
+
+/**
+ * An overridable {@link TrackOutput} implementation forwarding all methods to another track output.
+ */
+@UnstableApi
+public class ForwardingTrackOutput implements TrackOutput {
+
+  private final TrackOutput trackOutput;
+
+  /** Creates a new instance that forwards all operations to {@code trackOutput}. */
+  public ForwardingTrackOutput(TrackOutput trackOutput) {
+    this.trackOutput = trackOutput;
+  }
+
+  @Override
+  public void format(Format format) {
+    trackOutput.format(format);
+  }
+
+  @Override
+  public int sampleData(DataReader input, int length, boolean allowEndOfInput) throws IOException {
+    return trackOutput.sampleData(input, length, allowEndOfInput);
+  }
+
+  @Override
+  public void sampleData(ParsableByteArray data, int length) {
+    trackOutput.sampleData(data, length);
+  }
+
+  @Override
+  public int sampleData(
+      DataReader input, int length, boolean allowEndOfInput, @SampleDataPart int sampleDataPart)
+      throws IOException {
+    return trackOutput.sampleData(input, length, allowEndOfInput, sampleDataPart);
+  }
+
+  @Override
+  public void sampleData(ParsableByteArray data, int length, @SampleDataPart int sampleDataPart) {
+    trackOutput.sampleData(data, length, sampleDataPart);
+  }
+
+  @Override
+  public void sampleMetadata(
+      long timeUs,
+      @C.BufferFlags int flags,
+      int size,
+      int offset,
+      @Nullable CryptoData cryptoData) {
+    trackOutput.sampleMetadata(timeUs, flags, size, offset, cryptoData);
+  }
+}

libraries/extractor/src/test/java/androidx/media3/extractor/ForwardingTrackOutputTest.java

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+/*
+ * Copyright 2024 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package androidx.media3.extractor;
+
+import static com.google.common.truth.Truth.assertThat;
+
+import androidx.media3.test.utils.TestUtil;
+import androidx.test.ext.junit.runners.AndroidJUnit4;
+import java.lang.reflect.Method;
+import java.util.List;
+import org.junit.Test;
+import org.junit.runner.RunWith;
+
+/** Unit tests for {@link ForwardingTrackOutput}. */
+@RunWith(AndroidJUnit4.class)
+public class ForwardingTrackOutputTest {
+  @Test
+  public void forwardingTrackOutput_overridesAllMethods() throws NoSuchMethodException {
+    // Check with reflection that ForwardingTrackOutput overrides all TrackOutput methods.
+    List<Method> methods = TestUtil.getPublicMethods(TrackOutput.class);
+    for (Method method : methods) {
+      assertThat(
+              ForwardingTrackOutput.class
+                  .getDeclaredMethod(method.getName(), method.getParameterTypes())
+                  .getDeclaringClass())
+          .isEqualTo(ForwardingTrackOutput.class);
+    }
+  }
+}