1 files changed, 545 insertions, 0 deletions
diff --git a/mobile/android/exoplayer2/src/main/java/org/mozilla/thirdparty/com/google/android/exoplayer2/audio/AudioTrackPositionTracker.java b/mobile/android/exoplayer2/src/main/java/org/mozilla/thirdparty/com/google/android/exoplayer2/audio/AudioTrackPositionTracker.java
new file mode 100644
index 0000000000..e62e8cf2c5
--- /dev/null
+++ b/mobile/android/exoplayer2/src/main/java/org/mozilla/thirdparty/com/google/android/exoplayer2/audio/AudioTrackPositionTracker.java
@@ -0,0 +1,545 @@
+/*
+ * Copyright (C) 2018 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 org.mozilla.thirdparty.com.google.android.exoplayer2.audio;
+
+import static org.mozilla.thirdparty.com.google.android.exoplayer2.util.Util.castNonNull;
+
+import android.media.AudioTimestamp;
+import android.media.AudioTrack;
+import android.os.SystemClock;
+import androidx.annotation.IntDef;
+import androidx.annotation.Nullable;
+import org.mozilla.thirdparty.com.google.android.exoplayer2.C;
+import org.mozilla.thirdparty.com.google.android.exoplayer2.util.Assertions;
+import org.mozilla.thirdparty.com.google.android.exoplayer2.util.Util;
+import java.lang.annotation.Documented;
+import java.lang.annotation.Retention;
+import java.lang.annotation.RetentionPolicy;
+import java.lang.reflect.Method;
+
+/**
+ * Wraps an {@link AudioTrack}, exposing a position based on {@link
+ * AudioTrack#getPlaybackHeadPosition()} and {@link AudioTrack#getTimestamp(AudioTimestamp)}.
+ *
+ * <p>Call {@link #setAudioTrack(AudioTrack, int, int, int)} to set the audio track to wrap. Call
+ * {@link #mayHandleBuffer(long)} if there is input data to write to the track. If it returns false,
+ * the audio track position is stabilizing and no data may be written. Call {@link #start()}
+ * immediately before calling {@link AudioTrack#play()}. Call {@link #pause()} when pausing the
+ * track. Call {@link #handleEndOfStream(long)} when no more data will be written to the track. When
+ * the audio track will no longer be used, call {@link #reset()}.
+ */
+/* package */ final class AudioTrackPositionTracker {
+
+  /** Listener for position tracker events. */
+  public interface Listener {
+
+    /**
+     * Called when the frame position is too far from the expected frame position.
+     *
+     * @param audioTimestampPositionFrames The frame position of the last known audio track
+     *     timestamp.
+     * @param audioTimestampSystemTimeUs The system time associated with the last known audio track
+     *     timestamp, in microseconds.
+     * @param systemTimeUs The current time.
+     * @param playbackPositionUs The current playback head position in microseconds.
+     */
+    void onPositionFramesMismatch(
+        long audioTimestampPositionFrames,
+        long audioTimestampSystemTimeUs,
+        long systemTimeUs,
+        long playbackPositionUs);
+
+    /**
+     * Called when the system time associated with the last known audio track timestamp is
+     * unexpectedly far from the current time.
+     *
+     * @param audioTimestampPositionFrames The frame position of the last known audio track
+     *     timestamp.
+     * @param audioTimestampSystemTimeUs The system time associated with the last known audio track
+     *     timestamp, in microseconds.
+     * @param systemTimeUs The current time.
+     * @param playbackPositionUs The current playback head position in microseconds.
+     */
+    void onSystemTimeUsMismatch(
+        long audioTimestampPositionFrames,
+        long audioTimestampSystemTimeUs,
+        long systemTimeUs,
+        long playbackPositionUs);
+
+    /**
+     * Called when the audio track has provided an invalid latency.
+     *
+     * @param latencyUs The reported latency in microseconds.
+     */
+    void onInvalidLatency(long latencyUs);
+
+    /**
+     * Called when the audio track runs out of data to play.
+     *
+     * @param bufferSize The size of the sink's buffer, in bytes.
+     * @param bufferSizeMs The size of the sink's buffer, in milliseconds, if it is configured for
+     *     PCM output. {@link C#TIME_UNSET} if it is configured for encoded audio output, as the
+     *     buffered media can have a variable bitrate so the duration may be unknown.
+     */
+    void onUnderrun(int bufferSize, long bufferSizeMs);
+  }
+
+  /** {@link AudioTrack} playback states. */
+  @Documented
+  @Retention(RetentionPolicy.SOURCE)
+  @IntDef({PLAYSTATE_STOPPED, PLAYSTATE_PAUSED, PLAYSTATE_PLAYING})
+  private @interface PlayState {}
+  /** @see AudioTrack#PLAYSTATE_STOPPED */
+  private static final int PLAYSTATE_STOPPED = AudioTrack.PLAYSTATE_STOPPED;
+  /** @see AudioTrack#PLAYSTATE_PAUSED */
+  private static final int PLAYSTATE_PAUSED = AudioTrack.PLAYSTATE_PAUSED;
+  /** @see AudioTrack#PLAYSTATE_PLAYING */
+  private static final int PLAYSTATE_PLAYING = AudioTrack.PLAYSTATE_PLAYING;
+
+  /**
+   * AudioTrack timestamps are deemed spurious if they are offset from the system clock by more than
+   * this amount.
+   *
+   * <p>This is a fail safe that should not be required on correctly functioning devices.
+   */
+  private static final long MAX_AUDIO_TIMESTAMP_OFFSET_US = 5 * C.MICROS_PER_SECOND;
+
+  /**
+   * AudioTrack latencies are deemed impossibly large if they are greater than this amount.
+   *
+   * <p>This is a fail safe that should not be required on correctly functioning devices.
+   */
+  private static final long MAX_LATENCY_US = 5 * C.MICROS_PER_SECOND;
+
+  private static final long FORCE_RESET_WORKAROUND_TIMEOUT_MS = 200;
+
+  private static final int MAX_PLAYHEAD_OFFSET_COUNT = 10;
+  private static final int MIN_PLAYHEAD_OFFSET_SAMPLE_INTERVAL_US = 30000;
+  private static final int MIN_LATENCY_SAMPLE_INTERVAL_US = 500000;
+
+  private final Listener listener;
+  private final long[] playheadOffsets;
+
+  @Nullable private AudioTrack audioTrack;
+  private int outputPcmFrameSize;
+  private int bufferSize;
+  @Nullable private AudioTimestampPoller audioTimestampPoller;
+  private int outputSampleRate;
+  private boolean needsPassthroughWorkarounds;
+  private long bufferSizeUs;
+
+  private long smoothedPlayheadOffsetUs;
+  private long lastPlayheadSampleTimeUs;
+
+  @Nullable private Method getLatencyMethod;
+  private long latencyUs;
+  private boolean hasData;
+
+  private boolean isOutputPcm;
+  private long lastLatencySampleTimeUs;
+  private long lastRawPlaybackHeadPosition;
+  private long rawPlaybackHeadWrapCount;
+  private long passthroughWorkaroundPauseOffset;
+  private int nextPlayheadOffsetIndex;
+  private int playheadOffsetCount;
+  private long stopTimestampUs;
+  private long forceResetWorkaroundTimeMs;
+  private long stopPlaybackHeadPosition;
+  private long endPlaybackHeadPosition;
+
+  /**
+   * Creates a new audio track position tracker.
+   *
+   * @param listener A listener for position tracking events.
+   */
+  public AudioTrackPositionTracker(Listener listener) {
+    this.listener = Assertions.checkNotNull(listener);
+    if (Util.SDK_INT >= 18) {
+      try {
+        getLatencyMethod = AudioTrack.class.getMethod("getLatency", (Class<?>[]) null);
+      } catch (NoSuchMethodException e) {
+        // There's no guarantee this method exists. Do nothing.
+      }
+    }
+    playheadOffsets = new long[MAX_PLAYHEAD_OFFSET_COUNT];
+  }
+
+  /**
+   * Sets the {@link AudioTrack} to wrap. Subsequent method calls on this instance relate to this
+   * track's position, until the next call to {@link #reset()}.
+   *
+   * @param audioTrack The audio track to wrap.
+   * @param outputEncoding The encoding of the audio track.
+   * @param outputPcmFrameSize For PCM output encodings, the frame size. The value is ignored
+   *     otherwise.
+   * @param bufferSize The audio track buffer size in bytes.
+   */
+  public void setAudioTrack(
+      AudioTrack audioTrack,
+      @C.Encoding int outputEncoding,
+      int outputPcmFrameSize,
+      int bufferSize) {
+    this.audioTrack = audioTrack;
+    this.outputPcmFrameSize = outputPcmFrameSize;
+    this.bufferSize = bufferSize;
+    audioTimestampPoller = new AudioTimestampPoller(audioTrack);
+    outputSampleRate = audioTrack.getSampleRate();
+    needsPassthroughWorkarounds = needsPassthroughWorkarounds(outputEncoding);
+    isOutputPcm = Util.isEncodingLinearPcm(outputEncoding);
+    bufferSizeUs = isOutputPcm ? framesToDurationUs(bufferSize / outputPcmFrameSize) : C.TIME_UNSET;
+    lastRawPlaybackHeadPosition = 0;
+    rawPlaybackHeadWrapCount = 0;
+    passthroughWorkaroundPauseOffset = 0;
+    hasData = false;
+    stopTimestampUs = C.TIME_UNSET;
+    forceResetWorkaroundTimeMs = C.TIME_UNSET;
+    latencyUs = 0;
+  }
+
+  public long getCurrentPositionUs(boolean sourceEnded) {
+    if (Assertions.checkNotNull(this.audioTrack).getPlayState() == PLAYSTATE_PLAYING) {
+      maybeSampleSyncParams();
+    }
+
+    // If the device supports it, use the playback timestamp from AudioTrack.getTimestamp.
+    // Otherwise, derive a smoothed position by sampling the track's frame position.
+    long systemTimeUs = System.nanoTime() / 1000;
+    AudioTimestampPoller audioTimestampPoller = Assertions.checkNotNull(this.audioTimestampPoller);
+    if (audioTimestampPoller.hasTimestamp()) {
+      // Calculate the speed-adjusted position using the timestamp (which may be in the future).
+      long timestampPositionFrames = audioTimestampPoller.getTimestampPositionFrames();
+      long timestampPositionUs = framesToDurationUs(timestampPositionFrames);
+      if (!audioTimestampPoller.isTimestampAdvancing()) {
+        return timestampPositionUs;
+      }
+      long elapsedSinceTimestampUs = systemTimeUs - audioTimestampPoller.getTimestampSystemTimeUs();
+      return timestampPositionUs + elapsedSinceTimestampUs;
+    } else {
+      long positionUs;
+      if (playheadOffsetCount == 0) {
+        // The AudioTrack has started, but we don't have any samples to compute a smoothed position.
+        positionUs = getPlaybackHeadPositionUs();
+      } else {
+        // getPlaybackHeadPositionUs() only has a granularity of ~20 ms, so we base the position off
+        // the system clock (and a smoothed offset between it and the playhead position) so as to
+        // prevent jitter in the reported positions.
+        positionUs = systemTimeUs + smoothedPlayheadOffsetUs;
+      }
+      if (!sourceEnded) {
+        positionUs -= latencyUs;
+      }
+      return positionUs;
+    }
+  }
+
+  /** Starts position tracking. Must be called immediately before {@link AudioTrack#play()}. */
+  public void start() {
+    Assertions.checkNotNull(audioTimestampPoller).reset();
+  }
+
+  /** Returns whether the audio track is in the playing state. */
+  public boolean isPlaying() {
+    return Assertions.checkNotNull(audioTrack).getPlayState() == PLAYSTATE_PLAYING;
+  }
+
+  /**
+   * Checks the state of the audio track and returns whether the caller can write data to the track.
+   * Notifies {@link Listener#onUnderrun(int, long)} if the track has underrun.
+   *
+   * @param writtenFrames The number of frames that have been written.
+   * @return Whether the caller can write data to the track.
+   */
+  public boolean mayHandleBuffer(long writtenFrames) {
+    @PlayState int playState = Assertions.checkNotNull(audioTrack).getPlayState();
+    if (needsPassthroughWorkarounds) {
+      // An AC-3 audio track continues to play data written while it is paused. Stop writing so its
+      // buffer empties. See [Internal: b/18899620].
+      if (playState == PLAYSTATE_PAUSED) {
+        // We force an underrun to pause the track, so don't notify the listener in this case.
+        hasData = false;
+        return false;
+      }
+
+      // A new AC-3 audio track's playback position continues to increase from the old track's
+      // position for a short time after is has been released. Avoid writing data until the playback
+      // head position actually returns to zero.
+      if (playState == PLAYSTATE_STOPPED && getPlaybackHeadPosition() == 0) {
+        return false;
+      }
+    }
+
+    boolean hadData = hasData;
+    hasData = hasPendingData(writtenFrames);
+    if (hadData && !hasData && playState != PLAYSTATE_STOPPED && listener != null) {
+      listener.onUnderrun(bufferSize, C.usToMs(bufferSizeUs));
+    }
+
+    return true;
+  }
+
+  /**
+   * Returns an estimate of the number of additional bytes that can be written to the audio track's
+   * buffer without running out of space.
+   *
+   * <p>May only be called if the output encoding is one of the PCM encodings.
+   *
+   * @param writtenBytes The number of bytes written to the audio track so far.
+   * @return An estimate of the number of bytes that can be written.
+   */
+  public int getAvailableBufferSize(long writtenBytes) {
+    int bytesPending = (int) (writtenBytes - (getPlaybackHeadPosition() * outputPcmFrameSize));
+    return bufferSize - bytesPending;
+  }
+
+  /** Returns whether the track is in an invalid state and must be recreated. */
+  public boolean isStalled(long writtenFrames) {
+    return forceResetWorkaroundTimeMs != C.TIME_UNSET
+        && writtenFrames > 0
+        && SystemClock.elapsedRealtime() - forceResetWorkaroundTimeMs
+            >= FORCE_RESET_WORKAROUND_TIMEOUT_MS;
+  }
+
+  /**
+   * Records the writing position at which the stream ended, so that the reported position can
+   * continue to increment while remaining data is played out.
+   *
+   * @param writtenFrames The number of frames that have been written.
+   */
+  public void handleEndOfStream(long writtenFrames) {
+    stopPlaybackHeadPosition = getPlaybackHeadPosition();
+    stopTimestampUs = SystemClock.elapsedRealtime() * 1000;
+    endPlaybackHeadPosition = writtenFrames;
+  }
+
+  /**
+   * Returns whether the audio track has any pending data to play out at its current position.
+   *
+   * @param writtenFrames The number of frames written to the audio track.
+   * @return Whether the audio track has any pending data to play out.
+   */
+  public boolean hasPendingData(long writtenFrames) {
+    return writtenFrames > getPlaybackHeadPosition()
+        || forceHasPendingData();
+  }
+
+  /**
+   * Pauses the audio track position tracker, returning whether the audio track needs to be paused
+   * to cause playback to pause. If {@code false} is returned the audio track will pause without
+   * further interaction, as the end of stream has been handled.
+   */
+  public boolean pause() {
+    resetSyncParams();
+    if (stopTimestampUs == C.TIME_UNSET) {
+      // The audio track is going to be paused, so reset the timestamp poller to ensure it doesn't
+      // supply an advancing position.
+      Assertions.checkNotNull(audioTimestampPoller).reset();
+      return true;
+    }
+    // We've handled the end of the stream already, so there's no need to pause the track.
+    return false;
+  }
+
+  /**
+   * Resets the position tracker. Should be called when the audio track previous passed to {@link
+   * #setAudioTrack(AudioTrack, int, int, int)} is no longer in use.
+   */
+  public void reset() {
+    resetSyncParams();
+    audioTrack = null;
+    audioTimestampPoller = null;
+  }
+
+  private void maybeSampleSyncParams() {
+    long playbackPositionUs = getPlaybackHeadPositionUs();
+    if (playbackPositionUs == 0) {
+      // The AudioTrack hasn't output anything yet.
+      return;
+    }
+    long systemTimeUs = System.nanoTime() / 1000;
+    if (systemTimeUs - lastPlayheadSampleTimeUs >= MIN_PLAYHEAD_OFFSET_SAMPLE_INTERVAL_US) {
+      // Take a new sample and update the smoothed offset between the system clock and the playhead.
+      playheadOffsets[nextPlayheadOffsetIndex] = playbackPositionUs - systemTimeUs;
+      nextPlayheadOffsetIndex = (nextPlayheadOffsetIndex + 1) % MAX_PLAYHEAD_OFFSET_COUNT;
+      if (playheadOffsetCount < MAX_PLAYHEAD_OFFSET_COUNT) {
+        playheadOffsetCount++;
+      }
+      lastPlayheadSampleTimeUs = systemTimeUs;
+      smoothedPlayheadOffsetUs = 0;
+      for (int i = 0; i < playheadOffsetCount; i++) {
+        smoothedPlayheadOffsetUs += playheadOffsets[i] / playheadOffsetCount;
+      }
+    }
+
+    if (needsPassthroughWorkarounds) {
+      // Don't sample the timestamp and latency if this is an AC-3 passthrough AudioTrack on
+      // platform API versions 21/22, as incorrect values are returned. See [Internal: b/21145353].
+      return;
+    }
+
+    maybePollAndCheckTimestamp(systemTimeUs, playbackPositionUs);
+    maybeUpdateLatency(systemTimeUs);
+  }
+
+  private void maybePollAndCheckTimestamp(long systemTimeUs, long playbackPositionUs) {
+    AudioTimestampPoller audioTimestampPoller = Assertions.checkNotNull(this.audioTimestampPoller);
+    if (!audioTimestampPoller.maybePollTimestamp(systemTimeUs)) {
+      return;
+    }
+
+    // Perform sanity checks on the timestamp and accept/reject it.
+    long audioTimestampSystemTimeUs = audioTimestampPoller.getTimestampSystemTimeUs();
+    long audioTimestampPositionFrames = audioTimestampPoller.getTimestampPositionFrames();
+    if (Math.abs(audioTimestampSystemTimeUs - systemTimeUs) > MAX_AUDIO_TIMESTAMP_OFFSET_US) {
+      listener.onSystemTimeUsMismatch(
+          audioTimestampPositionFrames,
+          audioTimestampSystemTimeUs,
+          systemTimeUs,
+          playbackPositionUs);
+      audioTimestampPoller.rejectTimestamp();
+    } else if (Math.abs(framesToDurationUs(audioTimestampPositionFrames) - playbackPositionUs)
+        > MAX_AUDIO_TIMESTAMP_OFFSET_US) {
+      listener.onPositionFramesMismatch(
+          audioTimestampPositionFrames,
+          audioTimestampSystemTimeUs,
+          systemTimeUs,
+          playbackPositionUs);
+      audioTimestampPoller.rejectTimestamp();
+    } else {
+      audioTimestampPoller.acceptTimestamp();
+    }
+  }
+
+  private void maybeUpdateLatency(long systemTimeUs) {
+    if (isOutputPcm
+        && getLatencyMethod != null
+        && systemTimeUs - lastLatencySampleTimeUs >= MIN_LATENCY_SAMPLE_INTERVAL_US) {
+      try {
+        // Compute the audio track latency, excluding the latency due to the buffer (leaving
+        // latency due to the mixer and audio hardware driver).
+        latencyUs =
+            castNonNull((Integer) getLatencyMethod.invoke(Assertions.checkNotNull(audioTrack)))
+                    * 1000L
+                - bufferSizeUs;
+        // Sanity check that the latency is non-negative.
+        latencyUs = Math.max(latencyUs, 0);
+        // Sanity check that the latency isn't too large.
+        if (latencyUs > MAX_LATENCY_US) {
+          listener.onInvalidLatency(latencyUs);
+          latencyUs = 0;
+        }
+      } catch (Exception e) {
+        // The method existed, but doesn't work. Don't try again.
+        getLatencyMethod = null;
+      }
+      lastLatencySampleTimeUs = systemTimeUs;
+    }
+  }
+
+  private long framesToDurationUs(long frameCount) {
+    return (frameCount * C.MICROS_PER_SECOND) / outputSampleRate;
+  }
+
+  private void resetSyncParams() {
+    smoothedPlayheadOffsetUs = 0;
+    playheadOffsetCount = 0;
+    nextPlayheadOffsetIndex = 0;
+    lastPlayheadSampleTimeUs = 0;
+  }
+
+  /**
+   * If passthrough workarounds are enabled, pausing is implemented by forcing the AudioTrack to
+   * underrun. In this case, still behave as if we have pending data, otherwise writing won't
+   * resume.
+   */
+  private boolean forceHasPendingData() {
+    return needsPassthroughWorkarounds
+        && Assertions.checkNotNull(audioTrack).getPlayState() == AudioTrack.PLAYSTATE_PAUSED
+        && getPlaybackHeadPosition() == 0;
+  }
+
+  /**
+   * Returns whether to work around problems with passthrough audio tracks. See [Internal:
+   * b/18899620, b/19187573, b/21145353].
+   */
+  private static boolean needsPassthroughWorkarounds(@C.Encoding int outputEncoding) {
+    return Util.SDK_INT < 23
+        && (outputEncoding == C.ENCODING_AC3 || outputEncoding == C.ENCODING_E_AC3);
+  }
+
+  private long getPlaybackHeadPositionUs() {
+    return framesToDurationUs(getPlaybackHeadPosition());
+  }
+
+  /**
+   * {@link AudioTrack#getPlaybackHeadPosition()} returns a value intended to be interpreted as an
+   * unsigned 32 bit integer, which also wraps around periodically. This method returns the playback
+   * head position as a long that will only wrap around if the value exceeds {@link Long#MAX_VALUE}
+   * (which in practice will never happen).
+   *
+   * @return The playback head position, in frames.
+   */
+  private long getPlaybackHeadPosition() {
+    AudioTrack audioTrack = Assertions.checkNotNull(this.audioTrack);
+    if (stopTimestampUs != C.TIME_UNSET) {
+      // Simulate the playback head position up to the total number of frames submitted.
+      long elapsedTimeSinceStopUs = (SystemClock.elapsedRealtime() * 1000) - stopTimestampUs;
+      long framesSinceStop = (elapsedTimeSinceStopUs * outputSampleRate) / C.MICROS_PER_SECOND;
+      return Math.min(endPlaybackHeadPosition, stopPlaybackHeadPosition + framesSinceStop);
+    }
+
+    int state = audioTrack.getPlayState();
+    if (state == PLAYSTATE_STOPPED) {
+      // The audio track hasn't been started.
+      return 0;
+    }
+
+    long rawPlaybackHeadPosition = 0xFFFFFFFFL & audioTrack.getPlaybackHeadPosition();
+    if (needsPassthroughWorkarounds) {
+      // Work around an issue with passthrough/direct AudioTracks on platform API versions 21/22
+      // where the playback head position jumps back to zero on paused passthrough/direct audio
+      // tracks. See [Internal: b/19187573].
+      if (state == PLAYSTATE_PAUSED && rawPlaybackHeadPosition == 0) {
+        passthroughWorkaroundPauseOffset = lastRawPlaybackHeadPosition;
+      }
+      rawPlaybackHeadPosition += passthroughWorkaroundPauseOffset;
+    }
+
+    if (Util.SDK_INT <= 29) {
+      if (rawPlaybackHeadPosition == 0
+          && lastRawPlaybackHeadPosition > 0
+          && state == PLAYSTATE_PLAYING) {
+        // If connecting a Bluetooth audio device fails, the AudioTrack may be left in a state
+        // where its Java API is in the playing state, but the native track is stopped. When this
+        // happens the playback head position gets stuck at zero. In this case, return the old
+        // playback head position and force the track to be reset after
+        // {@link #FORCE_RESET_WORKAROUND_TIMEOUT_MS} has elapsed.
+        if (forceResetWorkaroundTimeMs == C.TIME_UNSET) {
+          forceResetWorkaroundTimeMs = SystemClock.elapsedRealtime();
+        }
+        return lastRawPlaybackHeadPosition;
+      } else {
+        forceResetWorkaroundTimeMs = C.TIME_UNSET;
+      }
+    }
+
+    if (lastRawPlaybackHeadPosition > rawPlaybackHeadPosition) {
+      // The value must have wrapped around.
+      rawPlaybackHeadWrapCount++;
+    }
+    lastRawPlaybackHeadPosition = rawPlaybackHeadPosition;
+    return rawPlaybackHeadPosition + (rawPlaybackHeadWrapCount << 32);
+  }
+}