diff --git a/content/media/nsBuiltinDecoderStateMachine.cpp b/content/media/nsBuiltinDecoderStateMachine.cpp
index 6bce566a33d9..48be18750d5d 100644
--- a/content/media/nsBuiltinDecoderStateMachine.cpp
+++ b/content/media/nsBuiltinDecoderStateMachine.cpp
@@ -164,7 +164,7 @@ PRBool nsBuiltinDecoderStateMachine::HasFutureAudio() const {
   mDecoder->GetMonitor().AssertCurrentThreadIn();
   PRBool aboveLowAudioThreshold = PR_FALSE;
   if (mAudioEndTime != -1) {
-    aboveLowAudioThreshold = mAudioEndTime - mCurrentFrameTime + mStartTime > LOW_AUDIO_MS;
+    aboveLowAudioThreshold = mAudioEndTime - GetMediaTime() > LOW_AUDIO_MS;
   }
   return HasAudio() &&
     !mAudioCompleted &&
@@ -259,7 +259,7 @@ void nsBuiltinDecoderStateMachine::DecodeLoop()
     PRInt64 audioDecoded = 0;
     {
       MonitorAutoEnter mon(mDecoder->GetMonitor());
-      currentTime = mCurrentFrameTime + mStartTime;
+      currentTime = GetMediaTime();
       audioDecoded = mReader->mAudioQueue.Duration();
       if (mAudioEndTime != -1) {
         audioDecoded += mAudioEndTime - currentTime;
@@ -451,7 +451,7 @@ void nsBuiltinDecoderStateMachine::AudioLoop()
         break;
       }
 
-      PRInt64 audioAhead = mAudioEndTime - mCurrentFrameTime - mStartTime;
+      PRInt64 audioAhead = mAudioEndTime - GetMediaTime();
       if (audioAhead > AMPLE_AUDIO_MS) {
         // We've pushed enough audio onto the hardware that we've queued up a
         // significant amount ahead of the playback position. The decode
@@ -653,7 +653,7 @@ void nsBuiltinDecoderStateMachine::UpdatePlaybackPosition(PRInt64 aTime)
   }
 
   // Notify DOM of any queued up audioavailable events
-  mEventManager.DispatchPendingEvents(mCurrentFrameTime + mStartTime);
+  mEventManager.DispatchPendingEvents(GetMediaTime());
 }
 
 void nsBuiltinDecoderStateMachine::ClearPositionChangeFlag()
@@ -989,6 +989,7 @@ nsresult nsBuiltinDecoderStateMachine::Run()
           StopPlayback(AUDIO_SHUTDOWN);
           StopDecodeThreads();
           ResetPlayback();
+          PRInt64 currentTime = GetMediaTime();
           nsresult res;
           {
             MonitorAutoExit exitMon(mDecoder->GetMonitor());
@@ -997,7 +998,7 @@ nsresult nsBuiltinDecoderStateMachine::Run()
             res = mReader->Seek(seekTime,
                                 mStartTime,
                                 mEndTime,
-                                mCurrentFrameTime + mStartTime);
+                                currentTime);
           }
           if (NS_SUCCEEDED(res)){
             PRInt64 audioTime = seekTime;
@@ -1035,7 +1036,7 @@ nsresult nsBuiltinDecoderStateMachine::Run()
         // if we need to seek again.
         
         nsCOMPtr<nsIRunnable> stopEvent;
-        if (mCurrentFrameTime == mEndTime) {
+        if (GetMediaTime() == mEndTime) {
           LOG(PR_LOG_DEBUG, ("%p Changed state from SEEKING (to %lldms) to COMPLETED",
                              mDecoder, seekTime));
           stopEvent = NS_NewRunnableMethod(mDecoder, &nsBuiltinDecoder::SeekingStoppedAtEnd);
diff --git a/content/media/nsBuiltinDecoderStateMachine.h b/content/media/nsBuiltinDecoderStateMachine.h
index a934911eec1c..ddc1e003ec0f 100644
--- a/content/media/nsBuiltinDecoderStateMachine.h
+++ b/content/media/nsBuiltinDecoderStateMachine.h
@@ -338,6 +338,16 @@ protected:
   // be held.
   PRBool IsPlaying();
 
+  // Returns the "media time". This is the absolute time which the media
+  // playback has reached. i.e. this returns values in the range
+  // [mStartTime, mEndTime], and mStartTime will not be 0 if the media does
+  // not start at 0. Note this is different to the value returned
+  // by GetCurrentTime(), which is in the range [0,duration].
+  PRInt64 GetMediaTime() const {
+    mDecoder->GetMonitor().AssertCurrentThreadIn();
+    return mStartTime + mCurrentFrameTime;
+  }
+
   // Monitor on mAudioStream. This monitor must be held in order to delete
   // or use the audio stream. This stops us destroying the audio stream
   // while it's being used on another thread (typically when it's being