Work around AudioTrack Bluetooth connection issue

If connecting a Bluetooth audio device fails, the AudioTrack may be left in a
bad state, where it is not actually playing and its position has jumped back to
zero. Detect and work around this case by resetting the track.

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=172600912

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

@@ -293,8 +293,6 @@ public final class DefaultAudioSink implements AudioSink {
 
   @Override
   public long getCurrentPositionUs(boolean sourceEnded) {
-    // If the device supports it, use the playback timestamp from AudioTrack.getTimestamp.
-    // Otherwise, derive a smoothed position by sampling the track's frame position.
     if (!hasCurrentPositionUs()) {
       return CURRENT_POSITION_NOT_SET;
     }
@@ -303,6 +301,8 @@ public final class DefaultAudioSink implements AudioSink {
       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 systemClockUs = System.nanoTime() / 1000;
     long positionUs;
     if (audioTimestampSet) {
@@ -638,6 +638,13 @@ public final class DefaultAudioSink implements AudioSink {
       inputBuffer = null;
       return true;
     }
+
+    if (audioTrackUtil.needsReset(getWrittenFrames())) {
+      Log.w(TAG, "Resetting stalled audio track");
+      reset();
+      return true;
+    }
+
     return false;
   }
 
@@ -1292,6 +1299,8 @@ public final class DefaultAudioSink implements AudioSink {
    */
   private static class AudioTrackUtil {
 
+    private static final long FORCE_RESET_WORKAROUND_TIMEOUT_MS = 200;
+
     protected AudioTrack audioTrack;
     private boolean needsPassthroughWorkaround;
     private int sampleRate;
@@ -1300,6 +1309,7 @@ public final class DefaultAudioSink implements AudioSink {
     private long passthroughWorkaroundPauseOffset;
 
     private long stopTimestampUs;
+    private long forceResetWorkaroundTimeMs;
     private long stopPlaybackHeadPosition;
     private long endPlaybackHeadPosition;
 
@@ -1314,6 +1324,7 @@ public final class DefaultAudioSink implements AudioSink {
       this.audioTrack = audioTrack;
       this.needsPassthroughWorkaround = needsPassthroughWorkaround;
       stopTimestampUs = C.TIME_UNSET;
+      forceResetWorkaroundTimeMs = C.TIME_UNSET;
       lastRawPlaybackHeadPosition = 0;
       rawPlaybackHeadWrapCount = 0;
       passthroughWorkaroundPauseOffset = 0;
@@ -1348,6 +1359,17 @@ public final class DefaultAudioSink implements AudioSink {
       audioTrack.pause();
     }
 
+    /**
+     * Returns whether the track is in an invalid state and must be reset.
+     *
+     * @see #getPlaybackHeadPosition()
+     */
+    public boolean needsReset(long writtenFrames) {
+      return forceResetWorkaroundTimeMs != C.TIME_UNSET && writtenFrames > 0
+          && SystemClock.elapsedRealtime() - forceResetWorkaroundTimeMs
+              >= FORCE_RESET_WORKAROUND_TIMEOUT_MS;
+    }
+
     /**
      * {@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
@@ -1380,6 +1402,24 @@ public final class DefaultAudioSink implements AudioSink {
         }
         rawPlaybackHeadPosition += passthroughWorkaroundPauseOffset;
       }
+
+      if (Util.SDK_INT <= 26) {
+        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++;