diff --git a/media/libmedia/AudioTrack.cpp b/media/libmedia/AudioTrack.cpp
index d90e733..78ae37e 100644
--- a/media/libmedia/AudioTrack.cpp
+++ b/media/libmedia/AudioTrack.cpp
@@ -148,10 +148,8 @@
             mAudioTrackThread->requestExitAndWait();
             mAudioTrackThread.clear();
         }
-        if (mAudioTrack != 0) {
-            mAudioTrack->asBinder()->unlinkToDeath(mDeathNotifier, this);
-            mAudioTrack.clear();
-        }
+        mAudioTrack->asBinder()->unlinkToDeath(mDeathNotifier, this);
+        mAudioTrack.clear();
         IPCThreadState::self()->flushCommands();
         AudioSystem::releaseAudioSessionId(mSessionId);
     }
@@ -222,6 +220,7 @@
 
     AutoMutex lock(mLock);
 
+    // invariant that mAudioTrack != 0 is true only after set() returns successfully
     if (mAudioTrack != 0) {
         ALOGE("Track already in use");
         return INVALID_OPERATION;
@@ -965,6 +964,7 @@
         ALOGE("Could not get control block");
         return NO_INIT;
     }
+    // invariant that mAudioTrack != 0 is true only after set() returns successfully
     if (mAudioTrack != 0) {
         mAudioTrack->asBinder()->unlinkToDeath(mDeathNotifier, this);
         mDeathNotifier.clear();
@@ -1705,16 +1705,13 @@
 status_t AudioTrack::setParameters(const String8& keyValuePairs)
 {
     AutoMutex lock(mLock);
-    if (mAudioTrack != 0) {
-        return mAudioTrack->setParameters(keyValuePairs);
-    } else {
-        return NO_INIT;
-    }
+    return mAudioTrack->setParameters(keyValuePairs);
 }
 
 status_t AudioTrack::getTimestamp(AudioTimestamp& timestamp)
 {
-    return INVALID_OPERATION;
+    AutoMutex lock(mLock);
+    return mAudioTrack->getTimestamp(timestamp);
 }
 
 String8 AudioTrack::getParameters(const String8& keys)