Add some audio hooks.

This makes it easier to add an extension for adjusting
audio playback rate.

library/src/main/java/com/google/android/exoplayer/MediaCodecAudioTrackRenderer.java

@@ -68,7 +68,7 @@ public class MediaCodecAudioTrackRenderer extends MediaCodecTrackRenderer implem
   private static final String RAW_DECODER_NAME = "OMX.google.raw.decoder";
 
   private final EventListener eventListener;
-  private final AudioTrack audioTrack;
+  protected final AudioTrack audioTrack;
 
   private int audioSessionId;
   private long currentPositionUs;
@@ -294,6 +294,7 @@ public class MediaCodecAudioTrackRenderer extends MediaCodecTrackRenderer implem
 
     // If we are out of sync, allow currentPositionUs to jump backwards.
     if ((handleBufferResult & AudioTrack.RESULT_POSITION_DISCONTINUITY) != 0) {
+      handleDiscontinuity();
       allowPositionDiscontinuity = true;
     }
 
@@ -307,6 +308,10 @@ public class MediaCodecAudioTrackRenderer extends MediaCodecTrackRenderer implem
     return false;
   }
 
+  protected void handleDiscontinuity() {
+    // Do nothing
+  }
+
   @Override
   public void handleMessage(int messageType, Object message) throws ExoPlaybackException {
     if (messageType == MSG_SET_VOLUME) {

library/src/main/java/com/google/android/exoplayer/audio/AudioTrack.java

@@ -145,6 +145,8 @@ public final class AudioTrack {
   private static final int MIN_PLAYHEAD_OFFSET_SAMPLE_INTERVAL_US = 30000;
   private static final int MIN_TIMESTAMP_SAMPLE_INTERVAL_US = 500000;
 
+  private static final int DEFAULT_TIMESCALE_PERCENT = 100;
+
   /**
    * Whether to enable a workaround for an issue where an audio effect does not keep its session
    * active across releasing/initializing a new audio track, on platform API version < 21.
@@ -191,6 +193,7 @@ public final class AudioTrack {
   private long resumeSystemTimeUs;
   private long latencyUs;
   private float volume;
+  private int timeScalePercent;
 
   private byte[] temporaryBuffer;
   private int temporaryBufferOffset;
@@ -218,6 +221,7 @@ public final class AudioTrack {
     }
     playheadOffsets = new long[MAX_PLAYHEAD_OFFSET_COUNT];
     volume = 1.0f;
+    timeScalePercent = DEFAULT_TIMESCALE_PERCENT;
     startMediaTimeState = START_NOT_SET;
   }
 
@@ -477,7 +481,7 @@ public final class AudioTrack {
       } else {
         // Sanity check that bufferStartTime is consistent with the expected value.
         long expectedBufferStartTime = startMediaTimeUs
-            + framesToDurationUs(bytesToFrames(submittedBytes));
+            + (framesToDurationUs(bytesToFrames(submittedBytes)) * timeScalePercent) / 100;
         if (startMediaTimeState == START_IN_SYNC
             && Math.abs(expectedBufferStartTime - bufferStartTime) > 200000) {
           Log.e(TAG, "Discontinuity detected [expected " + expectedBufferStartTime + ", got "
@@ -586,6 +590,15 @@ public final class AudioTrack {
     }
   }
 
+  /**
+   * Updates the timescale percent for reporting current time
+   *
+   * @param timeScalePercent The new percent multiplier
+   */
+  public void setTimeScalePercent(int timeScalePercent) {
+    this.timeScalePercent = timeScalePercent;
+  }
+
   /**
    * Releases the underlying audio track asynchronously. Calling {@link #initialize} will block
    * until the audio track has been released, so it is safe to initialize immediately after