Do not queue empty input buffers.

Follow-up to a comment on
ac8e418f3d
Buffers that are useful to pass to the sample/passthrough pipeline
should either contain data or the end of input flag. Otherwise, passing
these buffers along is unnecessary and may even cause the decoder to
allocate a new input buffer which is wasteful.

PiperOrigin-RevId: 411060709

libraries/test_data/src/test/assets/transformerdumps/mp4/sample_sef_slow_motion.mp4.dump

@@ -298,6 +298,12 @@ sample:
   size = 1193
   isKeyFrame = false
   presentationTimeUs = 734083
+sample:
+  trackIndex = 0
+  dataHashCode = 820561200
+  size = 1252
+  isKeyFrame = true
+  presentationTimeUs = 201521
 sample:
   trackIndex = 1
   dataHashCode = -1554795381

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

@@ -122,7 +122,7 @@ import java.nio.ByteBuffer;
    * Attempts to write a sample to the muxer.
    *
    * @param trackType The {@link C.TrackType track type} of the sample.
-   * @param data The sample to write, or {@code null} if the sample is empty.
+   * @param data The sample to write.
    * @param isKeyFrame Whether the sample is a key frame.
    * @param presentationTimeUs The presentation time of the sample in microseconds.
    * @return Whether the sample was successfully written. This is {@code false} if the muxer hasn't
@@ -133,10 +133,7 @@ import java.nio.ByteBuffer;
    *     track of the given track type.
    */
   public boolean writeSample(
-      @C.TrackType int trackType,
-      @Nullable ByteBuffer data,
-      boolean isKeyFrame,
-      long presentationTimeUs) {
+      @C.TrackType int trackType, ByteBuffer data, boolean isKeyFrame, long presentationTimeUs) {
     int trackIndex = trackTypeToIndex.get(trackType, /* valueIfKeyNotFound= */ C.INDEX_UNSET);
     checkState(
         trackIndex != C.INDEX_UNSET,
@@ -144,8 +141,6 @@ import java.nio.ByteBuffer;
 
     if (!canWriteSampleOfType(trackType)) {
       return false;
-    } else if (data == null) {
-      return true;
     }
 
     muxer.writeSampleData(trackIndex, data, isKeyFrame, presentationTimeUs);

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

@@ -1,31 +0,0 @@
-/*
- * Copyright 2020 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 androidx.media3.decoder.DecoderInputBuffer;
-
-/** A sample transformer for a given track. */
-/* package */ interface SampleTransformer {
-
-  /**
-   * Transforms the data and metadata of the sample contained in {@code buffer}.
-   *
-   * @param buffer The sample to transform. If the sample {@link DecoderInputBuffer#data data} is
-   *     {@code null} after the execution of this method, the sample must be discarded.
-   */
-  void transformSample(DecoderInputBuffer buffer);
-}

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

@@ -18,7 +18,6 @@ package androidx.media3.transformer;
 
 import static androidx.media3.common.util.Assertions.checkArgument;
 import static androidx.media3.common.util.Assertions.checkState;
-import static androidx.media3.common.util.Util.castNonNull;
 import static androidx.media3.extractor.NalUnitUtil.NAL_START_CODE;
 import static java.lang.Math.min;
 
@@ -40,7 +39,7 @@ import java.util.List;
 import org.checkerframework.checker.nullness.qual.RequiresNonNull;
 
 /**
- * {@link SampleTransformer} that flattens SEF slow motion video samples.
+ * Sample transformer that flattens SEF slow motion video samples.
  *
  * <p>Such samples follow the ITU-T Recommendation H.264 with temporal SVC.
  *
@@ -50,7 +49,7 @@ import org.checkerframework.checker.nullness.qual.RequiresNonNull;
  * <p>The mathematical formulas used in this class are explained in [Internal ref:
  * http://go/exoplayer-sef-slomo-video-flattening].
  */
-/* package */ final class SefSlowMotionVideoSampleTransformer implements SampleTransformer {
+/* package */ final class SefSlowMotionFlattener {
 
   /**
    * The frame rate of SEF slow motion videos, in fps.
@@ -109,7 +108,7 @@ import org.checkerframework.checker.nullness.qual.RequiresNonNull;
    */
   private long frameTimeDeltaUs;
 
-  public SefSlowMotionVideoSampleTransformer(Format format) {
+  public SefSlowMotionFlattener(Format format) {
     scratch = new byte[NAL_START_CODE_LENGTH];
     MetadataInfo metadataInfo = getMetadataInfo(format.metadata);
     slowMotionData = metadataInfo.slowMotionData;
@@ -130,14 +129,20 @@ import org.checkerframework.checker.nullness.qual.RequiresNonNull;
     }
   }
 
-  @Override
-  public void transformSample(DecoderInputBuffer buffer) {
+  /**
+   * Applies slow motion flattening by either indicating that the buffer's data should be dropped or
+   * transforming it in place.
+   *
+   * @return Whether the buffer should be dropped.
+   */
+  @RequiresNonNull("#1.data")
+  public boolean dropOrTransformSample(DecoderInputBuffer buffer) {
     if (slowMotionData == null) {
       // The input is not an SEF slow motion video.
-      return;
+      return false;
     }
 
-    ByteBuffer data = castNonNull(buffer.data);
+    ByteBuffer data = buffer.data;
     int originalPosition = data.position();
     data.position(originalPosition + NAL_START_CODE_LENGTH);
     data.get(scratch, 0, 4); // Read nal_unit_header_svc_extension.
@@ -148,14 +153,14 @@ import org.checkerframework.checker.nullness.qual.RequiresNonNull;
         "Missing SVC extension prefix NAL unit.");
     int layer = (scratch[3] & 0xFF) >> 5;
     boolean shouldKeepFrame = processCurrentFrame(layer, buffer.timeUs);
-    // Update buffer timestamp regardless of whether the frame is dropped because the buffer might
-    // still be passed to a decoder if it contains an end of stream flag.
+    // Update the timestamp regardless of whether the buffer is dropped as the timestamp may be
+    // reused for the empty end-of-stream buffer.
     buffer.timeUs = getCurrentFrameOutputTimeUs(/* inputTimeUs= */ buffer.timeUs);
     if (shouldKeepFrame) {
       skipToNextNalUnit(data); // Skip over prefix_nal_unit_svc.
-    } else {
-      buffer.data = null;
+      return false;
     }
+    return true;
   }
 
   /**

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

@@ -17,6 +17,7 @@
 package androidx.media3.transformer;
 
 import static androidx.media3.common.util.Assertions.checkNotNull;
+import static androidx.media3.common.util.Assertions.checkStateNotNull;
 import static androidx.media3.exoplayer.source.SampleStream.FLAG_REQUIRE_FORMAT;
 
 import androidx.annotation.Nullable;
@@ -127,7 +128,7 @@ import org.checkerframework.checker.nullness.qual.RequiresNonNull;
     }
     if (!muxerWrapper.writeSample(
         getTrackType(),
-        samplePipelineOutputBuffer.data,
+        checkStateNotNull(samplePipelineOutputBuffer.data),
         /* isKeyFrame= */ true,
         samplePipelineOutputBuffer.timeUs)) {
       return false;
@@ -152,11 +153,15 @@ import org.checkerframework.checker.nullness.qual.RequiresNonNull;
     int result = readSource(getFormatHolder(), samplePipelineInputBuffer, /* readFlags= */ 0);
     switch (result) {
       case C.RESULT_BUFFER_READ:
+        if (samplePipelineInputBuffer.isEndOfStream()) {
+          samplePipeline.queueInputBuffer();
+          return false;
+        }
         mediaClock.updateTimeForTrackType(getTrackType(), samplePipelineInputBuffer.timeUs);
         samplePipelineInputBuffer.timeUs -= streamOffsetUs;
         samplePipelineInputBuffer.flip();
         samplePipeline.queueInputBuffer();
-        return !samplePipelineInputBuffer.isEndOfStream();
+        return true;
       case C.RESULT_FORMAT_READ:
         throw new IllegalStateException("Format changes are not supported.");
       case C.RESULT_NOTHING_READ:

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

@@ -17,6 +17,7 @@
 package androidx.media3.transformer;
 
 import static androidx.media3.common.util.Assertions.checkNotNull;
+import static androidx.media3.common.util.Assertions.checkStateNotNull;
 import static androidx.media3.exoplayer.source.SampleStream.FLAG_REQUIRE_FORMAT;
 
 import android.content.Context;
@@ -28,6 +29,7 @@ import androidx.media3.decoder.DecoderInputBuffer;
 import androidx.media3.exoplayer.ExoPlaybackException;
 import androidx.media3.exoplayer.FormatHolder;
 import androidx.media3.exoplayer.source.SampleStream.ReadDataResult;
+import java.nio.ByteBuffer;
 import org.checkerframework.checker.nullness.qual.EnsuresNonNullIf;
 import org.checkerframework.checker.nullness.qual.MonotonicNonNull;
 import org.checkerframework.checker.nullness.qual.RequiresNonNull;
@@ -40,7 +42,7 @@ import org.checkerframework.checker.nullness.qual.RequiresNonNull;
   private final Context context;
   private final DecoderInputBuffer decoderInputBuffer;
 
-  private @MonotonicNonNull SampleTransformer slowMotionSampleTransformer;
+  private @MonotonicNonNull SefSlowMotionFlattener sefSlowMotionFlattener;
   private @MonotonicNonNull SamplePipeline samplePipeline;
   private boolean muxerWrapperTrackAdded;
   private boolean muxerWrapperTrackEnded;
@@ -107,7 +109,7 @@ import org.checkerframework.checker.nullness.qual.RequiresNonNull;
       samplePipeline = new PassthroughSamplePipeline(decoderInputFormat);
     }
     if (transformation.flattenForSlowMotion) {
-      slowMotionSampleTransformer = new SefSlowMotionVideoSampleTransformer(decoderInputFormat);
+      sefSlowMotionFlattener = new SefSlowMotionFlattener(decoderInputFormat);
     }
     return true;
   }
@@ -141,7 +143,7 @@ import org.checkerframework.checker.nullness.qual.RequiresNonNull;
 
     if (!muxerWrapper.writeSample(
         getTrackType(),
-        samplePipelineOutputBuffer.data,
+        checkStateNotNull(samplePipelineOutputBuffer.data),
         samplePipelineOutputBuffer.isKeyFrame(),
         samplePipelineOutputBuffer.timeUs)) {
       return false;
@@ -172,17 +174,24 @@ import org.checkerframework.checker.nullness.qual.RequiresNonNull;
     int result = readSource(getFormatHolder(), samplePipelineInputBuffer, /* readFlags= */ 0);
     switch (result) {
       case C.RESULT_BUFFER_READ:
-        if (samplePipelineInputBuffer.data != null
-            && samplePipelineInputBuffer.data.position() > 0) {
-          mediaClock.updateTimeForTrackType(getTrackType(), samplePipelineInputBuffer.timeUs);
-          samplePipelineInputBuffer.timeUs -= streamOffsetUs;
-          samplePipelineInputBuffer.flip();
-          if (slowMotionSampleTransformer != null) {
-            slowMotionSampleTransformer.transformSample(samplePipelineInputBuffer);
+        if (samplePipelineInputBuffer.isEndOfStream()) {
+          samplePipeline.queueInputBuffer();
+          return false;
+        }
+        mediaClock.updateTimeForTrackType(getTrackType(), samplePipelineInputBuffer.timeUs);
+        samplePipelineInputBuffer.timeUs -= streamOffsetUs;
+        samplePipelineInputBuffer.flip();
+        if (sefSlowMotionFlattener != null) {
+          ByteBuffer data = checkStateNotNull(samplePipelineInputBuffer.data);
+          boolean shouldDropSample =
+              sefSlowMotionFlattener.dropOrTransformSample(samplePipelineInputBuffer);
+          if (shouldDropSample) {
+            data.clear();
+            return true;
           }
         }
         samplePipeline.queueInputBuffer();
-        return !samplePipelineInputBuffer.isEndOfStream();
+        return true;
       case C.RESULT_FORMAT_READ:
         throw new IllegalStateException("Format changes are not supported.");
       case C.RESULT_NOTHING_READ:

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

@@ -16,7 +16,7 @@
 
 package androidx.media3.transformer;
 
-import static androidx.media3.transformer.SefSlowMotionVideoSampleTransformer.INPUT_FRAME_RATE;
+import static androidx.media3.transformer.SefSlowMotionFlattener.INPUT_FRAME_RATE;
 import static com.google.common.truth.Truth.assertThat;
 
 import androidx.media3.common.C;
@@ -32,9 +32,9 @@ import java.util.List;
 import org.junit.Test;
 import org.junit.runner.RunWith;
 
-/** Unit tests for {@link SefSlowMotionVideoSampleTransformer}. */
+/** Unit tests for {@link SefSlowMotionFlattener}. */
 @RunWith(AndroidJUnit4.class)
-public class SefSlowMotionVideoSampleTransformerTest {
+public class SefSlowMotionFlattenerTest {
 
   /**
    * Sequence of temporal SVC layers in an SEF slow motion video track with a maximum layer of 3.
@@ -56,10 +56,9 @@ public class SefSlowMotionVideoSampleTransformerTest {
         createSefSlowMotionFormat(
             captureFrameRate, inputMaxLayer, Arrays.asList(segment1, segment2));
 
-    SefSlowMotionVideoSampleTransformer sampleTransformer =
-        new SefSlowMotionVideoSampleTransformer(format);
+    SefSlowMotionFlattener sefSlowMotionFlattener = new SefSlowMotionFlattener(format);
     List<Integer> outputLayers =
-        getKeptOutputLayers(sampleTransformer, LAYER_SEQUENCE_MAX_LAYER_THREE, frameCount);
+        getKeptOutputLayers(sefSlowMotionFlattener, LAYER_SEQUENCE_MAX_LAYER_THREE, frameCount);
 
     List<Integer> expectedLayers = Arrays.asList(0, 0, 1, 0, 0, 1, 2, 3, 0, 3, 2, 3, 1, 3, 0);
     assertThat(outputLayers).isEqualTo(expectedLayers);
@@ -78,10 +77,9 @@ public class SefSlowMotionVideoSampleTransformerTest {
         createSefSlowMotionFormat(
             captureFrameRate, inputMaxLayer, Arrays.asList(segment1, segment2));
 
-    SefSlowMotionVideoSampleTransformer sampleTransformer =
-        new SefSlowMotionVideoSampleTransformer(format);
+    SefSlowMotionFlattener sefSlowMotionFlattener = new SefSlowMotionFlattener(format);
     List<Integer> outputLayers =
-        getKeptOutputLayers(sampleTransformer, LAYER_SEQUENCE_MAX_LAYER_THREE, frameCount);
+        getKeptOutputLayers(sefSlowMotionFlattener, LAYER_SEQUENCE_MAX_LAYER_THREE, frameCount);
 
     List<Integer> expectedLayers =
         Arrays.asList(0, 1, 0, 3, 2, 3, 1, 3, 2, 3, 0, 1, 0, 1, 2, 3, 0, 3, 2, 3, 1, 3, 0, 1);
@@ -101,10 +99,9 @@ public class SefSlowMotionVideoSampleTransformerTest {
         createSefSlowMotionFormat(
             captureFrameRate, inputMaxLayer, Arrays.asList(segment1, segment2));
 
-    SefSlowMotionVideoSampleTransformer sampleTransformer =
-        new SefSlowMotionVideoSampleTransformer(format);
+    SefSlowMotionFlattener sefSlowMotionFlattener = new SefSlowMotionFlattener(format);
     List<Integer> outputLayers =
-        getKeptOutputLayers(sampleTransformer, LAYER_SEQUENCE_MAX_LAYER_THREE, frameCount);
+        getKeptOutputLayers(sefSlowMotionFlattener, LAYER_SEQUENCE_MAX_LAYER_THREE, frameCount);
 
     List<Integer> expectedLayers = Arrays.asList(0, 0, 1, 0, 2, 3, 1, 3, 0);
     assertThat(outputLayers).isEqualTo(expectedLayers);
@@ -129,10 +126,9 @@ public class SefSlowMotionVideoSampleTransformerTest {
             inputMaxLayer,
             Arrays.asList(segmentWithNoFrame1, segmentWithNoFrame2, segmentWithFrame));
 
-    SefSlowMotionVideoSampleTransformer sampleTransformer =
-        new SefSlowMotionVideoSampleTransformer(format);
+    SefSlowMotionFlattener sefSlowMotionFlattener = new SefSlowMotionFlattener(format);
     List<Integer> outputLayers =
-        getKeptOutputLayers(sampleTransformer, LAYER_SEQUENCE_MAX_LAYER_THREE, frameCount);
+        getKeptOutputLayers(sefSlowMotionFlattener, LAYER_SEQUENCE_MAX_LAYER_THREE, frameCount);
 
     List<Integer> expectedLayers = Arrays.asList(0, 0, 1);
     assertThat(outputLayers).isEqualTo(expectedLayers);
@@ -153,10 +149,9 @@ public class SefSlowMotionVideoSampleTransformerTest {
         createSefSlowMotionFormat(
             captureFrameRate, inputMaxLayer, Arrays.asList(segment1, segment2));
 
-    SefSlowMotionVideoSampleTransformer sampleTransformer =
-        new SefSlowMotionVideoSampleTransformer(format);
+    SefSlowMotionFlattener sefSlowMotionFlattener = new SefSlowMotionFlattener(format);
     List<Long> outputTimesUs =
-        getOutputTimesUs(sampleTransformer, LAYER_SEQUENCE_MAX_LAYER_THREE, frameCount);
+        getOutputTimesUs(sefSlowMotionFlattener, LAYER_SEQUENCE_MAX_LAYER_THREE, frameCount);
 
     // Test frame inside segment.
     assertThat(outputTimesUs.get(9))
@@ -181,10 +176,9 @@ public class SefSlowMotionVideoSampleTransformerTest {
         createSefSlowMotionFormat(
             captureFrameRate, inputMaxLayer, Arrays.asList(segment1, segment2));
 
-    SefSlowMotionVideoSampleTransformer sampleTransformer =
-        new SefSlowMotionVideoSampleTransformer(format);
+    SefSlowMotionFlattener sefSlowMotionFlattener = new SefSlowMotionFlattener(format);
     List<Long> outputTimesUs =
-        getOutputTimesUs(sampleTransformer, LAYER_SEQUENCE_MAX_LAYER_THREE, frameCount);
+        getOutputTimesUs(sefSlowMotionFlattener, LAYER_SEQUENCE_MAX_LAYER_THREE, frameCount);
 
     // Test frame inside segment.
     assertThat(outputTimesUs.get(9))
@@ -209,10 +203,9 @@ public class SefSlowMotionVideoSampleTransformerTest {
         createSefSlowMotionFormat(
             captureFrameRate, inputMaxLayer, Arrays.asList(segment1, segment2));
 
-    SefSlowMotionVideoSampleTransformer sampleTransformer =
-        new SefSlowMotionVideoSampleTransformer(format);
+    SefSlowMotionFlattener sefSlowMotionFlattener = new SefSlowMotionFlattener(format);
     List<Long> outputTimesUs =
-        getOutputTimesUs(sampleTransformer, LAYER_SEQUENCE_MAX_LAYER_THREE, frameCount);
+        getOutputTimesUs(sefSlowMotionFlattener, LAYER_SEQUENCE_MAX_LAYER_THREE, frameCount);
 
     // Test frame inside second segment.
     assertThat(outputTimesUs.get(9)).isEqualTo(136_250);
@@ -249,20 +242,20 @@ public class SefSlowMotionVideoSampleTransformerTest {
 
   /**
    * Returns a list containing the temporal SVC layers of the frames that should be kept according
-   * to {@link SefSlowMotionVideoSampleTransformer#processCurrentFrame(int, long)}.
+   * to {@link SefSlowMotionFlattener#processCurrentFrame(int, long)}.
    *
-   * @param sampleTransformer The {@link SefSlowMotionVideoSampleTransformer}.
+   * @param sefSlowMotionFlattener The {@link SefSlowMotionFlattener}.
    * @param layerSequence The sequence of layer values in the input.
    * @param frameCount The number of video frames in the input.
    * @return The output layers.
    */
   private static List<Integer> getKeptOutputLayers(
-      SefSlowMotionVideoSampleTransformer sampleTransformer, int[] layerSequence, int frameCount) {
+      SefSlowMotionFlattener sefSlowMotionFlattener, int[] layerSequence, int frameCount) {
     List<Integer> outputLayers = new ArrayList<>();
     for (int i = 0; i < frameCount; i++) {
       int layer = layerSequence[i % layerSequence.length];
       long timeUs = i * C.MICROS_PER_SECOND / INPUT_FRAME_RATE;
-      if (sampleTransformer.processCurrentFrame(layer, timeUs)) {
+      if (sefSlowMotionFlattener.processCurrentFrame(layer, timeUs)) {
         outputLayers.add(layer);
       }
     }
@@ -271,24 +264,24 @@ public class SefSlowMotionVideoSampleTransformerTest {
 
   /**
    * Returns a list containing the frame output times obtained using {@link
-   * SefSlowMotionVideoSampleTransformer#getCurrentFrameOutputTimeUs(long)}.
+   * SefSlowMotionFlattener#getCurrentFrameOutputTimeUs(long)}.
    *
    * <p>The output contains the output times for all the input frames, regardless of whether they
    * should be kept or not.
    *
-   * @param sampleTransformer The {@link SefSlowMotionVideoSampleTransformer}.
+   * @param sefSlowMotionFlattener The {@link SefSlowMotionFlattener}.
    * @param layerSequence The sequence of layer values in the input.
    * @param frameCount The number of video frames in the input.
    * @return The frame output times, in microseconds.
    */
   private static List<Long> getOutputTimesUs(
-      SefSlowMotionVideoSampleTransformer sampleTransformer, int[] layerSequence, int frameCount) {
+      SefSlowMotionFlattener sefSlowMotionFlattener, int[] layerSequence, int frameCount) {
     List<Long> outputTimesUs = new ArrayList<>();
     for (int i = 0; i < frameCount; i++) {
       int layer = layerSequence[i % layerSequence.length];
       long inputTimeUs = i * C.MICROS_PER_SECOND / INPUT_FRAME_RATE;
-      sampleTransformer.processCurrentFrame(layer, inputTimeUs);
-      outputTimesUs.add(sampleTransformer.getCurrentFrameOutputTimeUs(inputTimeUs));
+      sefSlowMotionFlattener.processCurrentFrame(layer, inputTimeUs);
+      outputTimesUs.add(sefSlowMotionFlattener.getCurrentFrameOutputTimeUs(inputTimeUs));
     }
     return outputTimesUs;
   }