Add an option to force a silent audio track.

PiperOrigin-RevId: 492154544

libraries/test_data/src/test/assets/transformerdumps/mp4/sample.mp4.silentaudio.dump

@@ -0,0 +1,467 @@
+format 0:
+  id = 1
+  sampleMimeType = video/avc
+  codecs = avc1.64001F
+  maxInputSize = 36722
+  width = 1080
+  height = 720
+  frameRate = 29.970028
+  initializationData:
+    data = length 29, hash 4746B5D9
+    data = length 10, hash 7A0D0F2B
+format 1:
+  sampleMimeType = audio/mp4a-latm
+  channelCount = 2
+  sampleRate = 44100
+  pcmEncoding = 2
+sample:
+  trackIndex = 1
+  dataHashCode = 1742602241
+  size = 4096
+  isKeyFrame = true
+  presentationTimeUs = 0
+sample:
+  trackIndex = 1
+  dataHashCode = 1742602241
+  size = 4096
+  isKeyFrame = true
+  presentationTimeUs = 23220
+sample:
+  trackIndex = 1
+  dataHashCode = 1742602241
+  size = 4096
+  isKeyFrame = true
+  presentationTimeUs = 46440
+sample:
+  trackIndex = 1
+  dataHashCode = 1742602241
+  size = 4096
+  isKeyFrame = true
+  presentationTimeUs = 69660
+sample:
+  trackIndex = 1
+  dataHashCode = 1742602241
+  size = 4096
+  isKeyFrame = true
+  presentationTimeUs = 92880
+sample:
+  trackIndex = 1
+  dataHashCode = 1742602241
+  size = 4096
+  isKeyFrame = true
+  presentationTimeUs = 116100
+sample:
+  trackIndex = 1
+  dataHashCode = 1742602241
+  size = 4096
+  isKeyFrame = true
+  presentationTimeUs = 139320
+sample:
+  trackIndex = 1
+  dataHashCode = 1742602241
+  size = 4096
+  isKeyFrame = true
+  presentationTimeUs = 162540
+sample:
+  trackIndex = 1
+  dataHashCode = 1742602241
+  size = 4096
+  isKeyFrame = true
+  presentationTimeUs = 185760
+sample:
+  trackIndex = 1
+  dataHashCode = 1742602241
+  size = 4096
+  isKeyFrame = true
+  presentationTimeUs = 208980
+sample:
+  trackIndex = 1
+  dataHashCode = 1742602241
+  size = 4096
+  isKeyFrame = true
+  presentationTimeUs = 232200
+sample:
+  trackIndex = 1
+  dataHashCode = 1742602241
+  size = 4096
+  isKeyFrame = true
+  presentationTimeUs = 255420
+sample:
+  trackIndex = 1
+  dataHashCode = 1742602241
+  size = 4096
+  isKeyFrame = true
+  presentationTimeUs = 278640
+sample:
+  trackIndex = 1
+  dataHashCode = 1742602241
+  size = 4096
+  isKeyFrame = true
+  presentationTimeUs = 301860
+sample:
+  trackIndex = 1
+  dataHashCode = 1742602241
+  size = 4096
+  isKeyFrame = true
+  presentationTimeUs = 325080
+sample:
+  trackIndex = 1
+  dataHashCode = 1742602241
+  size = 4096
+  isKeyFrame = true
+  presentationTimeUs = 348300
+sample:
+  trackIndex = 1
+  dataHashCode = 1742602241
+  size = 4096
+  isKeyFrame = true
+  presentationTimeUs = 371520
+sample:
+  trackIndex = 1
+  dataHashCode = 1742602241
+  size = 4096
+  isKeyFrame = true
+  presentationTimeUs = 394740
+sample:
+  trackIndex = 1
+  dataHashCode = 1742602241
+  size = 4096
+  isKeyFrame = true
+  presentationTimeUs = 417960
+sample:
+  trackIndex = 1
+  dataHashCode = 1742602241
+  size = 4096
+  isKeyFrame = true
+  presentationTimeUs = 441180
+sample:
+  trackIndex = 1
+  dataHashCode = 1742602241
+  size = 4096
+  isKeyFrame = true
+  presentationTimeUs = 464400
+sample:
+  trackIndex = 1
+  dataHashCode = 1742602241
+  size = 4096
+  isKeyFrame = true
+  presentationTimeUs = 487620
+sample:
+  trackIndex = 1
+  dataHashCode = 1742602241
+  size = 4096
+  isKeyFrame = true
+  presentationTimeUs = 510840
+sample:
+  trackIndex = 0
+  dataHashCode = -770308242
+  size = 36692
+  isKeyFrame = true
+  presentationTimeUs = 0
+sample:
+  trackIndex = 0
+  dataHashCode = -732087136
+  size = 5312
+  isKeyFrame = false
+  presentationTimeUs = 66733
+sample:
+  trackIndex = 1
+  dataHashCode = 1742602241
+  size = 4096
+  isKeyFrame = true
+  presentationTimeUs = 534059
+sample:
+  trackIndex = 1
+  dataHashCode = 1742602241
+  size = 4096
+  isKeyFrame = true
+  presentationTimeUs = 557279
+sample:
+  trackIndex = 1
+  dataHashCode = 1742602241
+  size = 4096
+  isKeyFrame = true
+  presentationTimeUs = 580499
+sample:
+  trackIndex = 0
+  dataHashCode = 468156717
+  size = 599
+  isKeyFrame = false
+  presentationTimeUs = 33366
+sample:
+  trackIndex = 0
+  dataHashCode = 1150349584
+  size = 7735
+  isKeyFrame = false
+  presentationTimeUs = 200200
+sample:
+  trackIndex = 1
+  dataHashCode = 1742602241
+  size = 4096
+  isKeyFrame = true
+  presentationTimeUs = 603719
+sample:
+  trackIndex = 1
+  dataHashCode = 1742602241
+  size = 4096
+  isKeyFrame = true
+  presentationTimeUs = 626939
+sample:
+  trackIndex = 1
+  dataHashCode = 1742602241
+  size = 4096
+  isKeyFrame = true
+  presentationTimeUs = 650159
+sample:
+  trackIndex = 1
+  dataHashCode = 1742602241
+  size = 4096
+  isKeyFrame = true
+  presentationTimeUs = 673379
+sample:
+  trackIndex = 1
+  dataHashCode = 1742602241
+  size = 4096
+  isKeyFrame = true
+  presentationTimeUs = 696599
+sample:
+  trackIndex = 1
+  dataHashCode = 1742602241
+  size = 4096
+  isKeyFrame = true
+  presentationTimeUs = 719819
+sample:
+  trackIndex = 0
+  dataHashCode = 1443582006
+  size = 987
+  isKeyFrame = false
+  presentationTimeUs = 133466
+sample:
+  trackIndex = 0
+  dataHashCode = -310585145
+  size = 673
+  isKeyFrame = false
+  presentationTimeUs = 100100
+sample:
+  trackIndex = 0
+  dataHashCode = 807460688
+  size = 523
+  isKeyFrame = false
+  presentationTimeUs = 166833
+sample:
+  trackIndex = 0
+  dataHashCode = 1936487090
+  size = 6061
+  isKeyFrame = false
+  presentationTimeUs = 333666
+sample:
+  trackIndex = 1
+  dataHashCode = 1742602241
+  size = 4096
+  isKeyFrame = true
+  presentationTimeUs = 743039
+sample:
+  trackIndex = 1
+  dataHashCode = 1742602241
+  size = 4096
+  isKeyFrame = true
+  presentationTimeUs = 766259
+sample:
+  trackIndex = 1
+  dataHashCode = 1742602241
+  size = 4096
+  isKeyFrame = true
+  presentationTimeUs = 789479
+sample:
+  trackIndex = 1
+  dataHashCode = 1742602241
+  size = 4096
+  isKeyFrame = true
+  presentationTimeUs = 812699
+sample:
+  trackIndex = 1
+  dataHashCode = 1742602241
+  size = 4096
+  isKeyFrame = true
+  presentationTimeUs = 835919
+sample:
+  trackIndex = 0
+  dataHashCode = -32297181
+  size = 992
+  isKeyFrame = false
+  presentationTimeUs = 266933
+sample:
+  trackIndex = 0
+  dataHashCode = 1529616406
+  size = 623
+  isKeyFrame = false
+  presentationTimeUs = 233566
+sample:
+  trackIndex = 0
+  dataHashCode = 1949198785
+  size = 421
+  isKeyFrame = false
+  presentationTimeUs = 300300
+sample:
+  trackIndex = 0
+  dataHashCode = -147880287
+  size = 4899
+  isKeyFrame = false
+  presentationTimeUs = 433766
+sample:
+  trackIndex = 1
+  dataHashCode = 1742602241
+  size = 4096
+  isKeyFrame = true
+  presentationTimeUs = 859139
+sample:
+  trackIndex = 1
+  dataHashCode = 1742602241
+  size = 4096
+  isKeyFrame = true
+  presentationTimeUs = 882359
+sample:
+  trackIndex = 1
+  dataHashCode = 1742602241
+  size = 4096
+  isKeyFrame = true
+  presentationTimeUs = 905579
+sample:
+  trackIndex = 1
+  dataHashCode = 1742602241
+  size = 4096
+  isKeyFrame = true
+  presentationTimeUs = 928799
+sample:
+  trackIndex = 1
+  dataHashCode = 1742602241
+  size = 4096
+  isKeyFrame = true
+  presentationTimeUs = 952019
+sample:
+  trackIndex = 0
+  dataHashCode = 1369083472
+  size = 568
+  isKeyFrame = false
+  presentationTimeUs = 400400
+sample:
+  trackIndex = 0
+  dataHashCode = 965782073
+  size = 620
+  isKeyFrame = false
+  presentationTimeUs = 367033
+sample:
+  trackIndex = 0
+  dataHashCode = -261176150
+  size = 5450
+  isKeyFrame = false
+  presentationTimeUs = 567233
+sample:
+  trackIndex = 1
+  dataHashCode = 1742602241
+  size = 4096
+  isKeyFrame = true
+  presentationTimeUs = 975239
+sample:
+  trackIndex = 1
+  dataHashCode = 1742602241
+  size = 4096
+  isKeyFrame = true
+  presentationTimeUs = 998459
+sample:
+  trackIndex = 1
+  dataHashCode = -1029274849
+  size = 409
+  isKeyFrame = true
+  presentationTimeUs = 1021679
+sample:
+  trackIndex = 0
+  dataHashCode = -1830836678
+  size = 1051
+  isKeyFrame = false
+  presentationTimeUs = 500500
+sample:
+  trackIndex = 0
+  dataHashCode = 1767407540
+  size = 874
+  isKeyFrame = false
+  presentationTimeUs = 467133
+sample:
+  trackIndex = 0
+  dataHashCode = 918440283
+  size = 781
+  isKeyFrame = false
+  presentationTimeUs = 533866
+sample:
+  trackIndex = 0
+  dataHashCode = -1408463661
+  size = 4725
+  isKeyFrame = false
+  presentationTimeUs = 700700
+sample:
+  trackIndex = 0
+  dataHashCode = 1569455924
+  size = 1022
+  isKeyFrame = false
+  presentationTimeUs = 633966
+sample:
+  trackIndex = 0
+  dataHashCode = -1723778407
+  size = 790
+  isKeyFrame = false
+  presentationTimeUs = 600600
+sample:
+  trackIndex = 0
+  dataHashCode = 1578275472
+  size = 610
+  isKeyFrame = false
+  presentationTimeUs = 667333
+sample:
+  trackIndex = 0
+  dataHashCode = 1989768395
+  size = 2751
+  isKeyFrame = false
+  presentationTimeUs = 834166
+sample:
+  trackIndex = 0
+  dataHashCode = -1215674502
+  size = 745
+  isKeyFrame = false
+  presentationTimeUs = 767433
+sample:
+  trackIndex = 0
+  dataHashCode = -814473606
+  size = 621
+  isKeyFrame = false
+  presentationTimeUs = 734066
+sample:
+  trackIndex = 0
+  dataHashCode = 498370894
+  size = 505
+  isKeyFrame = false
+  presentationTimeUs = 800800
+sample:
+  trackIndex = 0
+  dataHashCode = -1051506468
+  size = 1268
+  isKeyFrame = false
+  presentationTimeUs = 967633
+sample:
+  trackIndex = 0
+  dataHashCode = -1025604144
+  size = 880
+  isKeyFrame = false
+  presentationTimeUs = 900900
+sample:
+  trackIndex = 0
+  dataHashCode = -913586520
+  size = 530
+  isKeyFrame = false
+  presentationTimeUs = 867533
+sample:
+  trackIndex = 0
+  dataHashCode = 1340459242
+  size = 568
+  isKeyFrame = false
+  presentationTimeUs = 934266
+released = true

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

@@ -41,6 +41,7 @@ import org.checkerframework.dataflow.qual.Pure;
 
   private static final int DEFAULT_ENCODER_BITRATE = 128 * 1024;
 
+  @Nullable private final SilentAudioGenerator silentAudioGenerator;
   private final DecoderInputBuffer inputBuffer;
   private final AudioProcessingPipeline audioProcessingPipeline;
   private final Codec encoder;
@@ -52,12 +53,14 @@ import org.checkerframework.dataflow.qual.Pure;
   private long nextEncoderInputBufferTimeUs;
   private long encoderBufferDurationRemainder;
 
+  // TODO(b/260618558): Move silent audio generation upstream of this component.
   public AudioTranscodingSamplePipeline(
       Format inputFormat,
       long streamStartPositionUs,
       long streamOffsetUs,
       TransformationRequest transformationRequest,
       ImmutableList<AudioProcessor> audioProcessors,
+      long forceSilentAudioDurationUs,
       Codec.EncoderFactory encoderFactory,
       MuxerWrapper muxerWrapper,
       Listener listener,
@@ -71,6 +74,16 @@ import org.checkerframework.dataflow.qual.Pure;
         muxerWrapper,
         listener);
 
+    if (forceSilentAudioDurationUs != C.TIME_UNSET) {
+      silentAudioGenerator =
+          new SilentAudioGenerator(
+              forceSilentAudioDurationUs,
+              inputFormat.sampleRate,
+              Util.getPcmFrameSize(C.ENCODING_PCM_16BIT, inputFormat.channelCount));
+    } else {
+      silentAudioGenerator = null;
+    }
+
     inputBuffer = new DecoderInputBuffer(BUFFER_REPLACEMENT_MODE_DISABLED);
     encoderInputBuffer = new DecoderInputBuffer(BUFFER_REPLACEMENT_MODE_DISABLED);
     encoderOutputBuffer = new DecoderInputBuffer(BUFFER_REPLACEMENT_MODE_DISABLED);
@@ -160,11 +173,17 @@ import org.checkerframework.dataflow.qual.Pure;
 
   @Override
   protected boolean processDataUpToMuxer() throws TransformationException {
-    if (audioProcessingPipeline.isOperational()) {
-      return feedEncoderFromProcessingPipeline() || feedProcessingPipelineFromInput();
-    } else {
-      return feedEncoderFromInput();
+    if (!audioProcessingPipeline.isOperational()) {
+      return silentAudioGenerator == null ? feedEncoderFromInput() : feedEncoderFromSilence();
     }
+
+    if (feedEncoderFromProcessingPipeline()) {
+      return true;
+    }
+
+    return silentAudioGenerator == null
+        ? feedProcessingPipelineFromInput()
+        : feedProcessingPipelineFromSilence();
   }
 
   @Override
@@ -268,6 +287,45 @@ import org.checkerframework.dataflow.qual.Pure;
     return true;
   }
 
+  /**
+   * Attempts to pass silent audio to the encoder.
+   *
+   * @return Whether it may be possible to feed more data immediately by calling this method again.
+   */
+  private boolean feedEncoderFromSilence() throws TransformationException {
+    checkNotNull(silentAudioGenerator);
+    if (!encoder.maybeDequeueInputBuffer(encoderInputBuffer)) {
+      return false;
+    }
+
+    if (silentAudioGenerator.isEnded()) {
+      queueEndOfStreamToEncoder();
+      return false;
+    }
+
+    ByteBuffer silence = silentAudioGenerator.getBuffer();
+    feedEncoder(silence);
+    return true;
+  }
+
+  /**
+   * Attempts to feed silent audio to the {@link AudioProcessingPipeline}.
+   *
+   * @return Whether it may be possible to feed more data immediately by calling this method again.
+   */
+  private boolean feedProcessingPipelineFromSilence() {
+    checkNotNull(silentAudioGenerator);
+    if (silentAudioGenerator.isEnded()) {
+      audioProcessingPipeline.queueEndOfStream();
+      return false;
+    }
+    checkState(!audioProcessingPipeline.isEnded());
+
+    ByteBuffer silence = silentAudioGenerator.getBuffer();
+    audioProcessingPipeline.queueInput(silence);
+    return !silence.hasRemaining();
+  }
+
   /**
    * Feeds as much data as possible between the current position and limit of the specified {@link
    * ByteBuffer} to the encoder, and advances its position by the number of bytes fed.

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

@@ -0,0 +1,51 @@
+/*
+ * Copyright 2022 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
+ *
+ *      http://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.transformer;
+
+import java.nio.ByteBuffer;
+import java.nio.ByteOrder;
+
+/* package */ final class SilentAudioGenerator {
+  private static final int DEFAULT_BUFFER_SIZE = 4096;
+
+  private final ByteBuffer internalBuffer;
+
+  private long remainingBytesToOutput;
+
+  public SilentAudioGenerator(long totalDurationUs, long sampleRate, int frameSize) {
+    remainingBytesToOutput = (sampleRate * frameSize * totalDurationUs) / 1_000_000L;
+    internalBuffer = ByteBuffer.allocate(DEFAULT_BUFFER_SIZE).order(ByteOrder.nativeOrder());
+    internalBuffer.flip();
+  }
+
+  public ByteBuffer getBuffer() {
+    if (!internalBuffer.hasRemaining()) {
+      // "next" buffer.
+      internalBuffer.clear();
+      if (remainingBytesToOutput < internalBuffer.capacity()) {
+        internalBuffer.limit((int) remainingBytesToOutput);
+      }
+      // Only reduce remaining bytes when we "generate" a new one.
+      remainingBytesToOutput -= internalBuffer.remaining();
+    }
+    return internalBuffer;
+  }
+
+  public boolean isEnded() {
+    return !internalBuffer.hasRemaining() && remainingBytesToOutput == 0;
+  }
+}

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

@@ -42,6 +42,7 @@ import androidx.media3.common.util.Util;
 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.DefaultMediaSourceFactory;
 import androidx.media3.exoplayer.source.MediaSource;
 import androidx.media3.extractor.DefaultExtractorsFactory;
@@ -88,6 +89,7 @@ public final class Transformer {
     private ImmutableList<Effect> videoEffects;
     private boolean removeAudio;
     private boolean removeVideo;
+    private boolean forceSilentAudio;
     private ListenerSet<Transformer.Listener> listeners;
     private MediaSource.@MonotonicNonNull Factory mediaSourceFactory;
     private Codec.DecoderFactory decoderFactory;
@@ -126,6 +128,7 @@ public final class Transformer {
       this.videoEffects = transformer.videoEffects;
       this.removeAudio = transformer.removeAudio;
       this.removeVideo = transformer.removeVideo;
+      this.forceSilentAudio = transformer.forceSilentAudio;
       this.listeners = transformer.listeners;
       this.mediaSourceFactory = transformer.mediaSourceFactory;
       this.decoderFactory = transformer.decoderFactory;
@@ -416,6 +419,33 @@ public final class Transformer {
       return this;
     }
 
+    /**
+     * Sets whether to force silent audio for the output file, ignoring any existing audio.
+     *
+     * <p>This method is experimental and may be removed or changed without warning.
+     *
+     * <p>Audio properties/format:
+     *
+     * <ul>
+     *   <li>Duration will match duration of the input media.
+     *   <li>Sample mime type will match {@link TransformationRequest#audioMimeType}, or {@link
+     *       MimeTypes#AUDIO_AAC} if {@code null}.
+     *   <li>Sample rate will be 44100hz. This can be modified by passing a {@link
+     *       SonicAudioProcessor} to {@link #setAudioProcessors(List)}, using {@link
+     *       SonicAudioProcessor#setOutputSampleRateHz(int)}.
+     *   <li>Channel count will be 2. This can be modified by implementing a custom {@link
+     *       AudioProcessor} and passing it to {@link #setAudioProcessors(List)}.
+     * </ul>
+     *
+     * @param forceSilentAudio Whether to output silent audio for the output file.
+     * @return This builder.
+     */
+    @CanIgnoreReturnValue
+    public Builder experimentalSetForceSilentAudio(boolean forceSilentAudio) {
+      this.forceSilentAudio = forceSilentAudio;
+      return this;
+    }
+
     /**
      * Builds a {@link Transformer} instance.
      *
@@ -445,6 +475,7 @@ public final class Transformer {
           videoEffects,
           removeAudio,
           removeVideo,
+          forceSilentAudio,
           listeners,
           mediaSourceFactory,
           decoderFactory,
@@ -557,6 +588,7 @@ public final class Transformer {
   private final ImmutableList<Effect> videoEffects;
   private final boolean removeAudio;
   private final boolean removeVideo;
+  private final boolean forceSilentAudio;
   private final ListenerSet<Transformer.Listener> listeners;
   private final MediaSource.Factory mediaSourceFactory;
   private final FrameProcessor.Factory frameProcessorFactory;
@@ -574,7 +606,8 @@ public final class Transformer {
       ImmutableList<Effect> videoEffects,
       boolean removeAudio,
       boolean removeVideo,
-      ListenerSet<Transformer.Listener> listeners,
+      boolean forceSilentAudio,
+      ListenerSet<Listener> listeners,
       MediaSource.Factory mediaSourceFactory,
       Codec.DecoderFactory decoderFactory,
       Codec.EncoderFactory encoderFactory,
@@ -583,6 +616,10 @@ public final class Transformer {
       Looper looper,
       DebugViewProvider debugViewProvider,
       Clock clock) {
+    if (forceSilentAudio) {
+      removeAudio = true;
+    }
+    checkState(!removeVideo || !forceSilentAudio, "Silent only audio track needs a video track.");
     checkState(!removeAudio || !removeVideo, "Audio and video cannot both be removed.");
     this.context = context;
     this.transformationRequest = transformationRequest;
@@ -590,6 +627,7 @@ public final class Transformer {
     this.videoEffects = videoEffects;
     this.removeAudio = removeAudio;
     this.removeVideo = removeVideo;
+    this.forceSilentAudio = forceSilentAudio;
     this.listeners = listeners;
     this.mediaSourceFactory = mediaSourceFactory;
     this.decoderFactory = decoderFactory;
@@ -728,6 +766,7 @@ public final class Transformer {
             videoEffects,
             removeAudio,
             removeVideo,
+            forceSilentAudio,
             mediaSourceFactory,
             decoderFactory,
             encoderFactory,

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

@@ -97,6 +97,7 @@ import org.checkerframework.checker.nullness.qual.MonotonicNonNull;
   private final TransformationRequest transformationRequest;
   private final ImmutableList<AudioProcessor> audioProcessors;
   private final ImmutableList<Effect> videoEffects;
+  private final boolean forceSilentAudio;
   private final Codec.DecoderFactory decoderFactory;
   private final Codec.EncoderFactory encoderFactory;
   private final FrameProcessor.Factory frameProcessorFactory;
@@ -114,6 +115,7 @@ import org.checkerframework.checker.nullness.qual.MonotonicNonNull;
 
   @Nullable private DecoderInputBuffer pendingInputBuffer;
   private boolean isDrainingPipelines;
+  private int silentSamplePipelineIndex;
   private @Transformer.ProgressState int progressState;
   private long progressPositionMs;
   private long durationUs;
@@ -131,6 +133,7 @@ import org.checkerframework.checker.nullness.qual.MonotonicNonNull;
       ImmutableList<Effect> videoEffects,
       boolean removeAudio,
       boolean removeVideo,
+      boolean forceSilentAudio,
       MediaSource.Factory mediaSourceFactory,
       Codec.DecoderFactory decoderFactory,
       Codec.EncoderFactory encoderFactory,
@@ -145,6 +148,7 @@ import org.checkerframework.checker.nullness.qual.MonotonicNonNull;
     this.transformationRequest = transformationRequest;
     this.audioProcessors = audioProcessors;
     this.videoEffects = videoEffects;
+    this.forceSilentAudio = forceSilentAudio;
     this.decoderFactory = decoderFactory;
     this.encoderFactory = encoderFactory;
     this.frameProcessorFactory = frameProcessorFactory;
@@ -168,6 +172,7 @@ import org.checkerframework.checker.nullness.qual.MonotonicNonNull;
             componentListener,
             clock);
     samplePipelines = new ArrayList<>();
+    silentSamplePipelineIndex = C.INDEX_UNSET;
     dequeueBufferConditionVariable = new ConditionVariable();
     muxerWrapper =
         new MuxerWrapper(
@@ -258,6 +263,10 @@ import org.checkerframework.checker.nullness.qual.MonotonicNonNull;
     while (samplePipeline.processData()) {}
     pendingInputBuffer = samplePipeline.dequeueInputBuffer();
     dequeueBufferConditionVariable.open();
+
+    if (forceSilentAudio) {
+      while (samplePipelines.get(silentSamplePipelineIndex).processData()) {}
+    }
   }
 
   private void queueInputInternal(int samplePipelineIndex) throws TransformationException {
@@ -391,6 +400,11 @@ import org.checkerframework.checker.nullness.qual.MonotonicNonNull;
       trackRegistered = true;
       muxerWrapper.registerTrack();
       fallbackListener.registerTrack();
+
+      if (forceSilentAudio) {
+        muxerWrapper.registerTrack();
+        fallbackListener.registerTrack();
+      }
     }
 
     @Override
@@ -410,6 +424,23 @@ import org.checkerframework.checker.nullness.qual.MonotonicNonNull;
 
       int samplePipelineIndex = tracksAddedCount;
       tracksAddedCount++;
+
+      if (forceSilentAudio) {
+        Format silentAudioFormat =
+            new Format.Builder()
+                .setSampleMimeType(MimeTypes.AUDIO_AAC)
+                .setSampleRate(44100)
+                .setChannelCount(2)
+                .build();
+        SamplePipeline audioSamplePipeline =
+            getSamplePipeline(silentAudioFormat, streamStartPositionUs, streamOffsetUs);
+        internalHandler
+            .obtainMessage(MSG_REGISTER_SAMPLE_PIPELINE, audioSamplePipeline)
+            .sendToTarget();
+        silentSamplePipelineIndex = tracksAddedCount;
+        tracksAddedCount++;
+      }
+
       return new SamplePipelineInput(samplePipelineIndex, samplePipeline.expectsDecodedData());
     }
 
@@ -459,6 +490,7 @@ import org.checkerframework.checker.nullness.qual.MonotonicNonNull;
             streamOffsetUs,
             transformationRequest,
             audioProcessors,
+            forceSilentAudio ? durationUs : C.TIME_UNSET,
             encoderFactory,
             muxerWrapper,
             /* listener= */ this,
@@ -509,6 +541,10 @@ import org.checkerframework.checker.nullness.qual.MonotonicNonNull;
       if (!audioProcessors.isEmpty()) {
         return true;
       }
+      if (forceSilentAudio) {
+        return true;
+      }
+
       return false;
     }
 

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

@@ -0,0 +1,73 @@
+/*
+ * Copyright 2022 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
+ *
+ *      http://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.transformer;
+
+import static com.google.common.truth.Truth.assertThat;
+
+import androidx.test.ext.junit.runners.AndroidJUnit4;
+import java.nio.ByteBuffer;
+import org.junit.Test;
+import org.junit.runner.RunWith;
+
+/** Unit tests for {@link SilentAudioGenerator}. */
+@RunWith(AndroidJUnit4.class)
+public class SilentAudioGeneratorTest {
+
+  @Test
+  public void numberOfBytesProduced_isCorrect() {
+    SilentAudioGenerator generator =
+        new SilentAudioGenerator(
+            /* totalDurationUs= */ 3_000_000, /* sampleRate= */ 88_200, /* frameSize= */ 12);
+    int bytesOutput = 0;
+    while (!generator.isEnded()) {
+      ByteBuffer output = generator.getBuffer();
+      bytesOutput += output.remaining();
+      // "Consume" buffer.
+      output.position(output.limit());
+    }
+
+    // 88_200 * 12 * 3s = 3175200
+    assertThat(bytesOutput).isEqualTo(3_175_200);
+  }
+
+  @Test
+  public void lastBufferProduced_isCorrectSize() {
+    SilentAudioGenerator generator =
+        new SilentAudioGenerator(
+            /* totalDurationUs= */ 1_000_000, /* sampleRate= */ 44_100, /* frameSize= */ 4);
+
+    int currentBufferSize = 0;
+    while (!generator.isEnded()) {
+      ByteBuffer output = generator.getBuffer();
+      currentBufferSize = output.remaining();
+      // "Consume" buffer.
+      output.position(output.limit());
+    }
+
+    // Last buffer is smaller and only outputs the 'leftover' bytes.
+    // (44_100 * 4) % 4096 = 272
+    assertThat(currentBufferSize).isEqualTo(272);
+  }
+
+  @Test
+  public void totalBytesLowerThanDefaultBufferSize_smallBufferProduced() {
+    SilentAudioGenerator generator =
+        new SilentAudioGenerator(
+            /* totalDurationUs= */ 5_000, /* sampleRate= */ 48_000, /* frameSize= */ 4);
+    // 5_000 * 48_000 * 4 / 1_000_000 = 960
+    assertThat(generator.getBuffer().remaining()).isEqualTo(960);
+  }
+}

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

@@ -265,6 +265,21 @@ public final class TransformerEndToEndTest {
         context, testMuxer, getDumpFileName(FILE_AUDIO_VIDEO + ".novideo"));
   }
 
+  @Test
+  public void startTransformation_silentAudio_completesSuccessfully() throws Exception {
+    Transformer transformer =
+        createTransformerBuilder(/* enableFallback= */ false)
+            .experimentalSetForceSilentAudio(true)
+            .build();
+    MediaItem mediaItem = MediaItem.fromUri(ASSET_URI_PREFIX + FILE_AUDIO_VIDEO);
+
+    transformer.startTransformation(mediaItem, outputPath);
+    TransformerTestRunner.runUntilCompleted(transformer);
+
+    DumpFileAsserts.assertOutput(
+        context, testMuxer, getDumpFileName(FILE_AUDIO_VIDEO + ".silentaudio"));
+  }
+
   @Test
   public void startTransformation_withMultipleListeners_callsEachOnCompletion() throws Exception {
     Transformer.Listener mockListener1 = mock(Transformer.Listener.class);