--- a/dom/media/MediaDecoderStateMachine.cpp
+++ b/dom/media/MediaDecoderStateMachine.cpp
@@ -2653,43 +2653,37 @@ MediaDecoderStateMachine::MediaDecoderSt
   INIT_MIRROR(mPlaybackRateReliable, true),
   INIT_MIRROR(mDecoderPosition, 0),
   INIT_CANONICAL(mDuration, NullableTimeUnit()),
   INIT_CANONICAL(mIsShutdown, false),
   INIT_CANONICAL(mNextFrameStatus, MediaDecoderOwner::NEXT_FRAME_UNAVAILABLE),
   INIT_CANONICAL(mCurrentPosition, TimeUnit::Zero()),
   INIT_CANONICAL(mPlaybackOffset, 0),
   INIT_CANONICAL(mIsAudioDataAudible, false)
+#ifdef XP_WIN
+  , mShouldUseHiResTimers(Preferences::GetBool("media.hi-res-timers.enabled", true))
+#endif
 {
   MOZ_COUNT_CTOR(MediaDecoderStateMachine);
   NS_ASSERTION(NS_IsMainThread(), "Should be on main thread.");
 
   InitVideoQueuePrefs();
-
-#ifdef XP_WIN
-  // Ensure high precision timers are enabled on Windows, otherwise the state
-  // machine isn't woken up at reliable intervals to set the next frame, and we
-  // drop frames while painting. Note that multiple calls to this function
-  // per-process is OK, provided each call is matched by a corresponding
-  // timeEndPeriod() call.
-  timeBeginPeriod(1);
-#endif
 }
 
 #undef INIT_WATCHABLE
 #undef INIT_MIRROR
 #undef INIT_CANONICAL
 
 MediaDecoderStateMachine::~MediaDecoderStateMachine()
 {
   MOZ_ASSERT(NS_IsMainThread(), "Should be on main thread.");
   MOZ_COUNT_DTOR(MediaDecoderStateMachine);
 
 #ifdef XP_WIN
-  timeEndPeriod(1);
+  MOZ_ASSERT(!mHiResTimersRequested);
 #endif
 }
 
 void
 MediaDecoderStateMachine::InitializationTask(MediaDecoder* aDecoder)
 {
   MOZ_ASSERT(OnTaskQueue());
 
@@ -2890,16 +2884,22 @@ MediaDecoderStateMachine::StopPlayback()
   MOZ_ASSERT(OnTaskQueue());
   LOG("StopPlayback()");
 
   mOnPlaybackEvent.Notify(MediaEventType::PlaybackStopped);
 
   if (IsPlaying()) {
     mMediaSink->SetPlaying(false);
     MOZ_ASSERT(!IsPlaying());
+#ifdef XP_WIN
+    if (mHiResTimersRequested) {
+      mHiResTimersRequested = false;
+      timeEndPeriod(1);
+    }
+#endif
   }
 }
 
 void MediaDecoderStateMachine::MaybeStartPlayback()
 {
   MOZ_ASSERT(OnTaskQueue());
   // Should try to start playback only after decoding first frames.
   MOZ_ASSERT(mSentFirstFrameLoadedEvent);
@@ -2913,16 +2913,30 @@ void MediaDecoderStateMachine::MaybeStar
     LOG("Not starting playback [mPlayState=%d]", mPlayState.Ref());
     return;
   }
 
   LOG("MaybeStartPlayback() starting playback");
   mOnPlaybackEvent.Notify(MediaEventType::PlaybackStarted);
   StartMediaSink();
 
+#ifdef XP_WIN
+  if (!mHiResTimersRequested && mShouldUseHiResTimers) {
+    mHiResTimersRequested = true;
+    // Ensure high precision timers are enabled on Windows, otherwise the state
+    // machine isn't woken up at reliable intervals to set the next frame, and we
+    // drop frames while painting. Note that each call must be matched by a
+    // corresponding timeEndPeriod() call. Enabling high precision timers causes
+    // the CPU to wake up more frequently on Windows 7 and earlier, which causes
+    // more CPU load and battery use. So we only enable high precision timers
+    // when we're actually playing.
+    timeBeginPeriod(1);
+  }
+#endif
+
   if (!IsPlaying()) {
     mMediaSink->SetPlaying(true);
     MOZ_ASSERT(IsPlaying());
   }
 }
 
 void
 MediaDecoderStateMachine::UpdatePlaybackPositionInternal(const TimeUnit& aTime)

--- a/dom/media/MediaDecoderStateMachine.h
+++ b/dom/media/MediaDecoderStateMachine.h
@@ -774,13 +774,24 @@ public:
   AbstractCanonical<int64_t>* CanonicalPlaybackOffset()
   {
     return &mPlaybackOffset;
   }
   AbstractCanonical<bool>* CanonicalIsAudioDataAudible()
   {
     return &mIsAudioDataAudible;
   }
+
+#ifdef XP_WIN
+  // Whether we've called timeBeginPeriod(1) to request high resolution
+  // timers. We request high resolution timers when playback starts, and
+  // turn them off when playback is paused. Enabling high resolution
+  // timers can cause higher CPU usage and battery drain on Windows 7.
+  bool mHiResTimersRequested = false;
+  // Whether we should enable high resolution timers. This is initialized at
+  // MDSM construction, and mirrors the value of media.hi-res-timers.enabled.
+  const bool mShouldUseHiResTimers;
+#endif
 };
 
 } // namespace mozilla
 
 #endif