Fix a race condition in AudioGraphInput

AudioGraphInput.onMediaItemChanged is called on input thread. Pending
media item changes are processed on processing thread, inside calls to
getOutput().
This change allows multiple pending media item changes to be enqueued,
and processed in sequence.

PiperOrigin-RevId: 638995291

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

@@ -36,7 +36,6 @@ import androidx.media3.common.audio.ChannelMixingAudioProcessor;
 import androidx.media3.common.audio.ChannelMixingMatrix;
 import androidx.media3.common.audio.SonicAudioProcessor;
 import androidx.media3.common.audio.SpeedChangingAudioProcessor;
-import androidx.media3.common.util.NullableType;
 import androidx.media3.common.util.Util;
 import androidx.media3.decoder.DecoderInputBuffer;
 import com.google.common.collect.ImmutableList;
@@ -45,7 +44,6 @@ import java.nio.ByteOrder;
 import java.util.Queue;
 import java.util.concurrent.ConcurrentLinkedQueue;
 import java.util.concurrent.atomic.AtomicLong;
-import java.util.concurrent.atomic.AtomicReference;
 
 /**
  * Processes a single sequential stream of PCM audio samples.
@@ -64,7 +62,7 @@ import java.util.concurrent.atomic.AtomicReference;
 
   private final Queue<DecoderInputBuffer> availableInputBuffers;
   private final Queue<DecoderInputBuffer> pendingInputBuffers;
-  private final AtomicReference<@NullableType MediaItemChange> pendingMediaItemChange;
+  private final Queue<MediaItemChange> pendingMediaItemChanges;
   private final AtomicLong startTimeUs;
 
   // silentAudioGenerator.audioFormat must match the current media item's input format.
@@ -103,7 +101,7 @@ import java.util.concurrent.atomic.AtomicReference;
       availableInputBuffers.add(inputBuffer);
     }
     pendingInputBuffers = new ConcurrentLinkedQueue<>();
-    pendingMediaItemChange = new AtomicReference<>();
+    pendingMediaItemChanges = new ConcurrentLinkedQueue<>();
     silentAudioGenerator = new SilentAudioGenerator(inputAudioFormat);
     audioProcessingPipeline =
         configureProcessing(
@@ -138,7 +136,7 @@ import java.util.concurrent.atomic.AtomicReference;
       return outputBuffer;
     }
 
-    if (!hasDataToOutput() && pendingMediaItemChange.get() != null) {
+    if (!hasDataToOutput() && !pendingMediaItemChanges.isEmpty()) {
       configureForPendingMediaItemChange();
     }
 
@@ -167,7 +165,7 @@ import java.util.concurrent.atomic.AtomicReference;
       AudioFormat audioFormat = new AudioFormat(decodedFormat);
       checkState(isInputAudioFormatValid(audioFormat), /* errorMessage= */ audioFormat);
     }
-    pendingMediaItemChange.set(
+    pendingMediaItemChanges.add(
         new MediaItemChange(editedMediaItem, durationUs, decodedFormat, isLast));
   }
 
@@ -179,7 +177,7 @@ import java.util.concurrent.atomic.AtomicReference;
   @Override
   @Nullable
   public DecoderInputBuffer getInputBuffer() {
-    if (inputBlocked || (pendingMediaItemChange.get() != null)) {
+    if (inputBlocked || !pendingMediaItemChanges.isEmpty()) {
       return null;
     }
     return availableInputBuffers.peek();
@@ -195,7 +193,7 @@ import java.util.concurrent.atomic.AtomicReference;
     if (inputBlocked) {
       return false;
     }
-    checkState(pendingMediaItemChange.get() == null);
+    checkState(pendingMediaItemChanges.isEmpty());
     DecoderInputBuffer inputBuffer = availableInputBuffers.remove();
     pendingInputBuffers.add(inputBuffer);
     startTimeUs.compareAndSet(
@@ -235,7 +233,7 @@ import java.util.concurrent.atomic.AtomicReference;
    * <p>Should only be called if the input thread and processing thread are the same.
    */
   public void flush() {
-    pendingMediaItemChange.set(null);
+    pendingMediaItemChanges.clear();
     processedFirstMediaItemChange = true;
     if (!availableInputBuffers.isEmpty()) {
       // Clear first available buffer in case the caller wrote data in the input buffer without
@@ -279,7 +277,7 @@ import java.util.concurrent.atomic.AtomicReference;
     if (hasDataToOutput()) {
       return false;
     }
-    if (pendingMediaItemChange.get() != null) {
+    if (!pendingMediaItemChanges.isEmpty()) {
       return false;
     }
     if (currentItemExpectedInputDurationUs != C.TIME_UNSET) {
@@ -323,7 +321,7 @@ import java.util.concurrent.atomic.AtomicReference;
 
     @Nullable DecoderInputBuffer pendingInputBuffer = pendingInputBuffers.peek();
     if (pendingInputBuffer == null) {
-      if (pendingMediaItemChange.get() != null) {
+      if (!pendingMediaItemChanges.isEmpty()) {
         if (shouldAppendSilence()) {
           appendSilence();
           return true;
@@ -377,7 +375,7 @@ import java.util.concurrent.atomic.AtomicReference;
 
     @Nullable DecoderInputBuffer currentInputBuffer = pendingInputBuffers.poll();
     if (currentInputBuffer == null) {
-      if (pendingMediaItemChange.get() != null && shouldAppendSilence()) {
+      if (!pendingMediaItemChanges.isEmpty() && shouldAppendSilence()) {
         appendSilence();
       }
       return EMPTY_BUFFER;
@@ -439,7 +437,7 @@ import java.util.concurrent.atomic.AtomicReference;
    * through {@link #getOutput()}.
    */
   private void configureForPendingMediaItemChange() throws UnhandledAudioFormatException {
-    MediaItemChange pendingChange = checkStateNotNull(pendingMediaItemChange.get());
+    MediaItemChange pendingChange = checkStateNotNull(pendingMediaItemChanges.poll());
 
     currentItemInputBytesRead = 0;
     isCurrentItemLast = pendingChange.isLast;
@@ -476,7 +474,6 @@ import java.util.concurrent.atomic.AtomicReference;
               /* requiredOutputAudioFormat= */ outputAudioFormat);
     }
     audioProcessingPipeline.flush();
-    pendingMediaItemChange.set(null);
     receivedEndOfStreamFromInput = false;
     processedFirstMediaItemChange = true;
   }

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

@@ -481,6 +481,36 @@ public class AudioGraphInputTest {
     assertThat(bytesOutput).isEqualTo(expectedSampleCount * STEREO_44100.bytesPerFrame);
   }
 
+  @Test
+  public void getOutput_withThreeSilentMediaItemChanges_outputsCorrectAmountOfSilentBytes()
+      throws Exception {
+    AudioGraphInput audioGraphInput =
+        new AudioGraphInput(
+            /* requestedOutputAudioFormat= */ AudioFormat.NOT_SET,
+            /* editedMediaItem= */ FAKE_ITEM,
+            /* inputFormat= */ getPcmFormat(STEREO_44100));
+
+    audioGraphInput.onMediaItemChanged(
+        /* editedMediaItem= */ FAKE_ITEM,
+        /* durationUs= */ 200_000,
+        /* decodedFormat= */ null,
+        /* isLast= */ false);
+    audioGraphInput.onMediaItemChanged(
+        /* editedMediaItem= */ FAKE_ITEM,
+        /* durationUs= */ 300_000,
+        /* decodedFormat= */ null,
+        /* isLast= */ false);
+    audioGraphInput.onMediaItemChanged(
+        /* editedMediaItem= */ FAKE_ITEM,
+        /* durationUs= */ 500_000,
+        /* decodedFormat= */ null,
+        /* isLast= */ true);
+
+    int bytesOutput = drainAudioGraphInputUntilEnded(audioGraphInput).size();
+    long expectedSampleCount = Util.durationUsToSampleCount(1_000_000, STEREO_44100.sampleRate);
+    assertThat(bytesOutput).isEqualTo(expectedSampleCount * STEREO_44100.bytesPerFrame);
+  }
+
   @Test
   public void getOutput_withSilentMediaItemAndEffectsChange_outputsCorrectAmountOfSilentBytes()
       throws Exception {