diff --git a/include/media/AudioTrack.h b/include/media/AudioTrack.h
index a3cc396..72e51f9 100644
--- a/include/media/AudioTrack.h
+++ b/include/media/AudioTrack.h
@@ -430,7 +430,7 @@
      *  - NO_ERROR: successful operation
      *  - BAD_VALUE:  position is NULL
      */
-            status_t    getPosition(uint32_t *position) const;
+            status_t    getPosition(uint32_t *position);
 
     /* For static buffer mode only, this returns the current playback position in frames
      * relative to start of buffer.  It is analogous to the position units used by
@@ -581,6 +581,7 @@
      * if you need a high resolution mapping between frame position and presentation time,
      * consider implementing that at application level, based on the low resolution timestamps.
      * Returns NO_ERROR if timestamp is valid.
+     * The timestamp parameter is undefined on return, if status is not NO_ERROR.
      */
             status_t    getTimestamp(AudioTimestamp& timestamp);
 
@@ -639,7 +640,7 @@
 
             // caller must hold lock on mLock for all _l methods
 
-            status_t createTrack_l(size_t epoch);
+            status_t createTrack_l();
 
             // can only be called when mState != STATE_ACTIVE
             void flush_l();
@@ -659,6 +660,9 @@
             bool     isDirect_l() const
                 { return (mFlags & AUDIO_OUTPUT_FLAG_DIRECT) != 0; }
 
+            // increment mPosition by the delta of mServer, and return new value of mPosition
+            uint32_t updateAndGetPosition_l();
+
     // Next 4 fields may be changed if IAudioTrack is re-created, but always != 0
     sp<IAudioTrack>         mAudioTrack;
     sp<IMemory>             mCblkMemory;
@@ -731,6 +735,18 @@
     bool                    mMarkerReached;
     uint32_t                mNewPosition;           // in frames
     uint32_t                mUpdatePeriod;          // in frames, zero means no EVENT_NEW_POS
+    uint32_t                mServer;                // in frames, last known mProxy->getPosition()
+                                                    // which is count of frames consumed by server,
+                                                    // reset by new IAudioTrack,
+                                                    // whether it is reset by stop() is TBD
+    uint32_t                mPosition;              // in frames, like mServer except continues
+                                                    // monotonically after new IAudioTrack,
+                                                    // and could be easily widened to uint64_t
+    uint32_t                mReleased;              // in frames, count of frames released to server
+                                                    // but not necessarily consumed by server,
+                                                    // reset by stop() but continues monotonically
+                                                    // after new IAudioTrack to restore mPosition,
+                                                    // and could be easily widened to uint64_t
 
     audio_output_flags_t    mFlags;
         // const after set(), except for bits AUDIO_OUTPUT_FLAG_FAST and AUDIO_OUTPUT_FLAG_OFFLOAD.
diff --git a/include/media/IAudioTrack.h b/include/media/IAudioTrack.h
index 5c8a484..619ac78 100644
--- a/include/media/IAudioTrack.h
+++ b/include/media/IAudioTrack.h
@@ -88,7 +88,7 @@
     /* Send parameters to the audio hardware */
     virtual status_t    setParameters(const String8& keyValuePairs) = 0;
 
-    /* Return NO_ERROR if timestamp is valid */
+    /* Return NO_ERROR if timestamp is valid.  timestamp is undefined otherwise. */
     virtual status_t    getTimestamp(AudioTimestamp& timestamp) = 0;
 
     /* Signal the playback thread for a change in control block */
diff --git a/include/media/nbaio/NBAIO.h b/include/media/nbaio/NBAIO.h
index be0c15b..d422576 100644
--- a/include/media/nbaio/NBAIO.h
+++ b/include/media/nbaio/NBAIO.h
@@ -227,7 +227,7 @@
 
     // Returns NO_ERROR if a timestamp is available.  The timestamp includes the total number
     // of frames presented to an external observer, together with the value of CLOCK_MONOTONIC
-    // as of this presentation count.
+    // as of this presentation count.  The timestamp parameter is undefined if error is returned.
     virtual status_t getTimestamp(AudioTimestamp& timestamp) { return INVALID_OPERATION; }
 
 protected: