Add 'Keep every nth frame' frame dropping strategy.

#minor-release

PiperOrigin-RevId: 538804347
(cherry picked from commit 4bb7b3cddcddd228ed6d513b4e2ffa80268b2fbc)

library/effect/src/androidTest/java/com/google/android/exoplayer2/effect/FrameDropTest.java

+/*
+ * Copyright 2023 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 com.google.android.exoplayer2.effect;
+
+import static com.google.android.exoplayer2.testutil.BitmapPixelTestUtil.readBitmap;
+import static com.google.android.exoplayer2.util.Assertions.checkNotNull;
+import static com.google.android.exoplayer2.util.VideoFrameProcessor.INPUT_TYPE_BITMAP;
+import static com.google.common.truth.Truth.assertThat;
+
+import androidx.test.ext.junit.runners.AndroidJUnit4;
+import com.google.android.exoplayer2.C;
+import com.google.android.exoplayer2.testutil.VideoFrameProcessorTestRunner;
+import com.google.android.exoplayer2.video.ColorInfo;
+import com.google.common.collect.ImmutableList;
+import java.util.Queue;
+import java.util.concurrent.ConcurrentLinkedQueue;
+import org.checkerframework.checker.nullness.qual.EnsuresNonNull;
+import org.checkerframework.checker.nullness.qual.MonotonicNonNull;
+import org.checkerframework.checker.nullness.qual.RequiresNonNull;
+import org.junit.After;
+import org.junit.Before;
+import org.junit.Test;
+import org.junit.runner.RunWith;
+
+/** Tests for {@link FrameDropEffect}. */
+@RunWith(AndroidJUnit4.class)
+public class FrameDropTest {
+  private static final String ORIGINAL_PNG_ASSET_PATH =
+      "media/bitmap/sample_mp4_first_frame/electrical_colors/original.png";
+
+  private static final String SCALE_WIDE_PNG_ASSET_PATH =
+      "media/bitmap/sample_mp4_first_frame/electrical_colors/scale_wide.png";
+
+  private @MonotonicNonNull VideoFrameProcessorTestRunner videoFrameProcessorTestRunner;
+
+  private @MonotonicNonNull Queue<Long> actualPresentationTimesUs;
+
+  @EnsuresNonNull("actualPresentationTimesUs")
+  @Before
+  public void setUp() {
+    actualPresentationTimesUs = new ConcurrentLinkedQueue<>();
+  }
+
+  @After
+  public void release() {
+    checkNotNull(videoFrameProcessorTestRunner).release();
+  }
+
+  // TODO: b/536973872 - When support for testing multiple frames in the output, test whether the
+  //  correct frames comes out.
+  @RequiresNonNull("actualPresentationTimesUs")
+  @Test
+  public void frameDrop_withDefaultStrategy_outputsFramesAtTheCorrectPresentationTimesUs()
+      throws Exception {
+    String testId = "frameDrop_withDefaultStrategy_outputsFramesAtTheCorrectPresentationTimesUs";
+    videoFrameProcessorTestRunner =
+        getDefaultFrameProcessorTestRunnerBuilder(
+                testId, FrameDropEffect.createDefaultFrameDropEffect(/* targetFrameRate= */ 30))
+            .setOnOutputFrameAvailableForRenderingListener(actualPresentationTimesUs::add)
+            .build();
+
+    ImmutableList<Integer> timestampsMs = ImmutableList.of(0, 16, 32, 48, 58, 71, 86);
+    for (int timestampMs : timestampsMs) {
+      videoFrameProcessorTestRunner.queueInputBitmap(
+          readBitmap(ORIGINAL_PNG_ASSET_PATH),
+          /* durationUs= */ C.MICROS_PER_SECOND,
+          /* offsetToAddUs= */ timestampMs * 1000L,
+          /* frameRate= */ 1);
+    }
+    videoFrameProcessorTestRunner.endFrameProcessing();
+
+    assertThat(actualPresentationTimesUs).containsExactly(0L, 32_000L, 71_000L).inOrder();
+  }
+
+  @RequiresNonNull("actualPresentationTimesUs")
+  @Test
+  public void frameDrop_withSimpleStrategy_outputsFramesAtTheCorrectPresentationTimesUs()
+      throws Exception {
+    String testId = "frameDrop_withSimpleStrategy_outputsFramesAtTheCorrectPresentationTimesUs";
+    videoFrameProcessorTestRunner =
+        getDefaultFrameProcessorTestRunnerBuilder(
+                testId,
+                FrameDropEffect.createSimpleFrameDropEffect(
+                    /* expectedFrameRate= */ 6, /* targetFrameRate= */ 2))
+            .build();
+
+    videoFrameProcessorTestRunner.queueInputBitmap(
+        readBitmap(ORIGINAL_PNG_ASSET_PATH),
+        /* durationUs= */ C.MICROS_PER_SECOND,
+        /* offsetToAddUs= */ 0L,
+        /* frameRate= */ 4);
+    videoFrameProcessorTestRunner.queueInputBitmap(
+        readBitmap(SCALE_WIDE_PNG_ASSET_PATH),
+        /* durationUs= */ C.MICROS_PER_SECOND,
+        /* offsetToAddUs= */ C.MICROS_PER_SECOND,
+        /* frameRate= */ 2);
+    videoFrameProcessorTestRunner.endFrameProcessing();
+
+    assertThat(actualPresentationTimesUs).containsExactly(500_000L, 1_500_000L).inOrder();
+  }
+
+  @RequiresNonNull("actualPresentationTimesUs")
+  @Test
+  public void frameDrop_withSimpleStrategy_outputsAllFrames() throws Exception {
+    String testId = "frameDrop_withSimpleStrategy_outputsCorrectNumberOfFrames";
+    videoFrameProcessorTestRunner =
+        getDefaultFrameProcessorTestRunnerBuilder(
+                testId,
+                FrameDropEffect.createSimpleFrameDropEffect(
+                    /* expectedFrameRate= */ 3, /* targetFrameRate= */ 3))
+            .build();
+
+    videoFrameProcessorTestRunner.queueInputBitmap(
+        readBitmap(ORIGINAL_PNG_ASSET_PATH),
+        /* durationUs= */ C.MICROS_PER_SECOND,
+        /* offsetToAddUs= */ 0L,
+        /* frameRate= */ 3);
+    videoFrameProcessorTestRunner.endFrameProcessing();
+
+    assertThat(actualPresentationTimesUs).containsExactly(0L, 333_333L, 666_667L).inOrder();
+  }
+
+  @RequiresNonNull("actualPresentationTimesUs")
+  private VideoFrameProcessorTestRunner.Builder getDefaultFrameProcessorTestRunnerBuilder(
+      String testId, FrameDropEffect frameDropEffect) {
+    return new VideoFrameProcessorTestRunner.Builder()
+        .setTestId(testId)
+        .setVideoFrameProcessorFactory(new DefaultVideoFrameProcessor.Factory.Builder().build())
+        .setInputType(INPUT_TYPE_BITMAP)
+        .setInputColorInfo(ColorInfo.SRGB_BT709_FULL)
+        .setEffects(frameDropEffect)
+        .setOnOutputFrameAvailableForRenderingListener(actualPresentationTimesUs::add);
+  }
+}

library/effect/src/main/java/com/google/android/exoplayer2/effect/FrameDroppingShaderProgram.java → library/effect/src/main/java/com/google/android/exoplayer2/effect/DefaultFrameDroppingShaderProgram.java

@@ -25,7 +25,6 @@ import com.google.android.exoplayer2.C;
 import com.google.android.exoplayer2.util.GlTextureInfo;
 import com.google.android.exoplayer2.util.VideoFrameProcessingException;
 
-// TODO(b/227625363): Add tests for this file.
 /**
  * Drops frames by only queuing input frames that are chosen by the frame dropping strategy.
  *
@@ -40,7 +39,7 @@ import com.google.android.exoplayer2.util.VideoFrameProcessingException;
  * <p>Where T_lastQueued is the timestamp of the last queued frame and T_(x+1) is the timestamp of
  * the next frame. The target frame interval is determined from {@code targetFps}.
  */
-/* package */ final class FrameDroppingShaderProgram extends FrameCacheGlShaderProgram {
+/* package */ final class DefaultFrameDroppingShaderProgram extends FrameCacheGlShaderProgram {
   private final long targetFrameDeltaUs;
 
   @Nullable private GlTextureInfo previousTexture;
@@ -56,7 +55,7 @@ import com.google.android.exoplayer2.util.VideoFrameProcessingException;
    *     in linear RGB BT.2020. If {@code false}, colors will be in linear RGB BT.709.
    * @param targetFps The number of frames per second the output video should roughly have.
    */
-  public FrameDroppingShaderProgram(Context context, boolean useHdr, float targetFps)
+  public DefaultFrameDroppingShaderProgram(Context context, boolean useHdr, float targetFps)
       throws VideoFrameProcessingException {
     super(context, /* capacity= */ 1, useHdr);
     this.targetFrameDeltaUs = (long) (C.MICROS_PER_SECOND / targetFps);

library/effect/src/main/java/com/google/android/exoplayer2/effect/FrameDropEffect.java

@@ -17,25 +17,62 @@
 package com.google.android.exoplayer2.effect;
 
 import android.content.Context;
+import com.google.android.exoplayer2.C;
 import com.google.android.exoplayer2.util.VideoFrameProcessingException;
 
 /** Drops frames to lower average frame rate to around {@code targetFrameRate}. */
 public class FrameDropEffect implements GlEffect {
 
+  private final float inputFrameRate;
   private final float targetFrameRate;
 
   /**
-   * Creates an instance.
+   * Creates a {@link FrameDropEffect} with the default frame dropping strategy.
+   *
+   * <p>The strategy used is to queue the current frame, x, with timestamp T_x if and only if one of
+   * the following is true:
+   *
+   * <ul>
+   *   <li>x is the first frame,
+   *   <li>(T_x - T_lastQueued) is closer to the target frame interval than (T_(x+1) - T_lastQueued)
+   * </ul>
+   *
+   * <p>Where T_lastQueued is the timestamp of the last queued frame and T_(x+1) is the timestamp of
+   * the next frame. The target frame interval is determined from {@code targetFrameRate}.
    *
    * @param targetFrameRate The number of frames per second the output video should roughly have.
    */
-  public FrameDropEffect(float targetFrameRate) {
-    this.targetFrameRate = targetFrameRate;
+  public static FrameDropEffect createDefaultFrameDropEffect(float targetFrameRate) {
+    return new FrameDropEffect(/* inputFrameRate= */ C.RATE_UNSET, targetFrameRate);
+  }
+
+  /**
+   * Creates a {@link FrameDropEffect} that keeps every nth frame, where n is the {@code
+   * inputFrameRate} divided by the {@code targetFrameRate}.
+   *
+   * <p>For example, if the input stream came in at 60fps and the targeted frame rate was 20fps,
+   * every 3rd frame would be kept. If n is not an integer, then we round to the nearest one.
+   *
+   * @param expectedFrameRate The number of frames per second in the input stream.
+   * @param targetFrameRate The number of frames per second the output video should roughly have.
+   */
+  public static FrameDropEffect createSimpleFrameDropEffect(
+      float expectedFrameRate, float targetFrameRate) {
+    return new FrameDropEffect(expectedFrameRate, targetFrameRate);
   }
 
   @Override
   public GlShaderProgram toGlShaderProgram(Context context, boolean useHdr)
       throws VideoFrameProcessingException {
-    return new FrameDroppingShaderProgram(context, useHdr, targetFrameRate);
+    if (inputFrameRate == C.RATE_UNSET) {
+      return new DefaultFrameDroppingShaderProgram(context, useHdr, targetFrameRate);
+    } else {
+      return new SimpleFrameDroppingShaderProgram(context, useHdr, inputFrameRate, targetFrameRate);
+    }
+  }
+
+  private FrameDropEffect(float inputFrameRate, float targetFrameRate) {
+    this.inputFrameRate = inputFrameRate;
+    this.targetFrameRate = targetFrameRate;
   }
 }

library/effect/src/main/java/com/google/android/exoplayer2/effect/SimpleFrameDroppingShaderProgram.java

+/*
+ * Copyright 2023 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 com.google.android.exoplayer2.effect;
+
+import static com.google.android.exoplayer2.util.Assertions.checkArgument;
+import static java.lang.Math.round;
+
+import android.content.Context;
+import com.google.android.exoplayer2.util.GlTextureInfo;
+import com.google.android.exoplayer2.util.VideoFrameProcessingException;
+
+/**
+ * Drops frames by only keeping every nth frame, where n is the {@code inputFrameRate} divided by
+ * the {@code targetFrameRate}.
+ *
+ * <p>For example, if the input stream came in at 60fps and the targeted frame rate was 20fps, every
+ * 3rd frame would be kept. If n is not an integer, then we round to the nearest one.
+ */
+/* package */ final class SimpleFrameDroppingShaderProgram extends FrameCacheGlShaderProgram {
+
+  private final int n;
+
+  private int framesReceived;
+
+  /**
+   * Creates a new instance.
+   *
+   * @param context The {@link Context}.
+   * @param useHdr Whether input textures come from an HDR source. If {@code true}, colors will be
+   *     in linear RGB BT.2020. If {@code false}, colors will be in linear RGB BT.709.
+   * @param inputFrameRate The number of frames per second the input stream should have.
+   * @param targetFrameRate The number of frames per second the output video should roughly have.
+   */
+  public SimpleFrameDroppingShaderProgram(
+      Context context, boolean useHdr, float inputFrameRate, float targetFrameRate)
+      throws VideoFrameProcessingException {
+    super(context, /* capacity= */ 1, useHdr);
+    n = round(inputFrameRate / targetFrameRate);
+    checkArgument(n >= 1, "The input frame rate should be greater than the target frame rate.");
+  }
+
+  @Override
+  public void queueInputFrame(GlTextureInfo inputTexture, long presentationTimeUs) {
+    framesReceived++;
+    if (framesReceived % n == 0) {
+      super.queueInputFrame(inputTexture, presentationTimeUs);
+    } else {
+      inputListener.onInputFrameProcessed(inputTexture);
+      inputListener.onReadyToAcceptInputFrame();
+    }
+  }
+}