Add skip silence option to PlaybackParameters

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=190917894

RELEASENOTES.md

@@ -37,6 +37,8 @@
   * Fix an issue where the playback position would pause just after playback
     begins, and poll the audio timestamp less frequently once it starts
     advancing ([#3841](https://github.com/google/ExoPlayer/issues/3841)).
+  * Add an option to skip silent audio in `PlaybackParameters`
+    ((#2635)[https://github.com/google/ExoPlayer/issues/2635]).
 * Caching:
   * Add release method to Cache interface.
   * Prevent multiple instances of SimpleCache in the same folder.

library/core/src/main/java/com/google/android/exoplayer2/PlaybackParameters.java

@@ -22,21 +22,19 @@ import com.google.android.exoplayer2.util.Assertions;
  */
 public final class PlaybackParameters {
 
-  /**
-   * The default playback parameters: real-time playback with no pitch modification.
-   */
-  public static final PlaybackParameters DEFAULT = new PlaybackParameters(1f, 1f);
+  /** The default playback parameters: real-time playback with no pitch modification. */
+  public static final PlaybackParameters DEFAULT =
+      new PlaybackParameters(/* speed= */ 1f, /* pitch= */ 1f, /* skipSilence= */ false);
 
-  /**
-   * The factor by which playback will be sped up.
-   */
+  /** The factor by which playback will be sped up. */
   public final float speed;
 
-  /**
-   * The factor by which the audio pitch will be scaled.
-   */
+  /** The factor by which the audio pitch will be scaled. */
   public final float pitch;
 
+  /** Whether to skip silence in the input. */
+  public final boolean skipSilence;
+
   private final int scaledUsPerMs;
 
   /**
@@ -46,10 +44,22 @@ public final class PlaybackParameters {
    * @param pitch The factor by which the audio pitch will be scaled. Must be greater than zero.
    */
   public PlaybackParameters(float speed, float pitch) {
+    this(speed, pitch, /* skipSilence= */ false);
+  }
+
+  /**
+   * Creates new playback parameters.
+   *
+   * @param speed The factor by which playback will be sped up. Must be greater than zero.
+   * @param pitch The factor by which the audio pitch will be scaled. Must be greater than zero.
+   * @param skipSilence Whether to skip silences in the audio stream.
+   */
+  public PlaybackParameters(float speed, float pitch, boolean skipSilence) {
     Assertions.checkArgument(speed > 0);
     Assertions.checkArgument(pitch > 0);
     this.speed = speed;
     this.pitch = pitch;
+    this.skipSilence = skipSilence;
     scaledUsPerMs = Math.round(speed * 1000f);
   }
 
@@ -73,14 +83,17 @@ public final class PlaybackParameters {
       return false;
     }
     PlaybackParameters other = (PlaybackParameters) obj;
-    return this.speed == other.speed && this.pitch == other.pitch;
+    return this.speed == other.speed
+        && this.pitch == other.pitch
+        && this.skipSilence == other.skipSilence;
   }
-  
+
   @Override
   public int hashCode() {
     int result = 17;
     result = 31 * result + Float.floatToRawIntBits(speed);
     result = 31 * result + Float.floatToRawIntBits(pitch);
+    result = 31 * result + (skipSilence ? 1 : 0);
     return result;
   }
 

library/core/src/main/java/com/google/android/exoplayer2/audio/DefaultAudioSink.java

@@ -738,9 +738,12 @@ public final class DefaultAudioSink implements AudioSink {
       this.playbackParameters = PlaybackParameters.DEFAULT;
       return this.playbackParameters;
     }
-    playbackParameters = new PlaybackParameters(
-        sonicAudioProcessor.setSpeed(playbackParameters.speed),
-        sonicAudioProcessor.setPitch(playbackParameters.pitch));
+    playbackParameters =
+        new PlaybackParameters(
+            sonicAudioProcessor.setSpeed(playbackParameters.speed),
+            sonicAudioProcessor.setPitch(playbackParameters.pitch),
+            playbackParameters.skipSilence);
+    silenceSkippingAudioProcessor.setEnabled(playbackParameters.skipSilence);
     PlaybackParameters lastSetPlaybackParameters =
         drainingPlaybackParameters != null ? drainingPlaybackParameters
             : !playbackParametersCheckpoints.isEmpty()

library/core/src/main/java/com/google/android/exoplayer2/util/EventLogger.java

@@ -115,8 +115,8 @@ public class EventLogger
   public void onPlaybackParametersChanged(PlaybackParameters playbackParameters) {
     logd(
         Util.formatInvariant(
-            "playbackParameters [speed=%.2f, pitch=%.2f]",
-            playbackParameters.speed, playbackParameters.pitch));
+            "playbackParameters [speed=%.2f, pitch=%.2f, skipSilence=%s]",
+            playbackParameters.speed, playbackParameters.pitch, playbackParameters.skipSilence));
   }
 
   @Override