--- a/dom/media/MediaDecoderStateMachine.cpp
+++ b/dom/media/MediaDecoderStateMachine.cpp
@@ -232,19 +232,16 @@ MediaDecoderStateMachine::MediaDecoderSt
   mAudioCaptured(false),
   mAudioCompleted(false, "MediaDecoderStateMachine::mAudioCompleted"),
   mVideoCompleted(false, "MediaDecoderStateMachine::mVideoCompleted"),
   mNotifyMetadataBeforeFirstFrame(false),
   mDispatchedEventToDecode(false),
   mQuickBuffering(false),
   mMinimizePreroll(false),
   mDecodeThreadWaiting(false),
-  mDropAudioUntilNextDiscontinuity(false),
-  mDropVideoUntilNextDiscontinuity(false),
-  mCurrentTimeBeforeSeek(0),
   mDecodingFirstFrame(true),
   mSentLoadedMetadataEvent(false),
   mSentFirstFrameLoadedEvent(false),
   mSentPlaybackEndedEvent(false),
   mOutputStreamManager(new OutputStreamManager()),
   mResource(aDecoder->GetResource()),
   mAudioOffloading(false),
   mSilentDataDuration(0),
@@ -572,46 +569,22 @@ MediaDecoderStateMachine::NeedToDecodeAu
              IsAudioDecoding(), mMinimizePreroll, HaveEnoughDecodedAudio());
 
   return IsAudioDecoding() &&
          mState != DECODER_STATE_SEEKING &&
          ((IsDecodingFirstFrame() && AudioQueue().GetSize() == 0) ||
           (!mMinimizePreroll && !HaveEnoughDecodedAudio()));
 }
 
-bool
-MediaDecoderStateMachine::IsAudioSeekComplete()
-{
-  MOZ_ASSERT(OnTaskQueue());
-  SAMPLE_LOG("IsAudioSeekComplete() curTarVal=%d mAudDis=%d aqFin=%d aqSz=%d",
-    mCurrentSeek.Exists(), mDropAudioUntilNextDiscontinuity, AudioQueue().IsFinished(), AudioQueue().GetSize());
-  return
-    !HasAudio() ||
-    (mCurrentSeek.Exists() &&
-     !mDropAudioUntilNextDiscontinuity &&
-     (AudioQueue().IsFinished() || AudioQueue().GetSize() > 0));
-}
-
-bool
-MediaDecoderStateMachine::IsVideoSeekComplete()
-{
-  MOZ_ASSERT(OnTaskQueue());
-  SAMPLE_LOG("IsVideoSeekComplete() curTarVal=%d mVidDis=%d vqFin=%d vqSz=%d",
-    mCurrentSeek.Exists(), mDropVideoUntilNextDiscontinuity, VideoQueue().IsFinished(), VideoQueue().GetSize());
-  return
-    !HasVideo() ||
-    (mCurrentSeek.Exists() &&
-     !mDropVideoUntilNextDiscontinuity &&
-     (VideoQueue().IsFinished() || VideoQueue().GetSize() > 0));
-}
-
 void
 MediaDecoderStateMachine::OnAudioDecoded(MediaData* aAudioSample)
 {
   MOZ_ASSERT(OnTaskQueue());
+  MOZ_ASSERT(mState != DECODER_STATE_SEEKING);
+
   RefPtr<MediaData> audio(aAudioSample);
   MOZ_ASSERT(audio);
   mAudioDataRequest.Complete();
 
   // audio->GetEndTime() is not always mono-increasing in chained ogg.
   mDecodedAudioEndTime = std::max(audio->GetEndTime(), mDecodedAudioEndTime);
 
   SAMPLE_LOG("OnAudioDecoded [%lld,%lld] disc=%d",
@@ -634,53 +607,16 @@ MediaDecoderStateMachine::OnAudioDecoded
         return;
       }
       if (mIsAudioPrerolling && DonePrerollingAudio()) {
         StopPrerollingAudio();
       }
       return;
     }
 
-    case DECODER_STATE_SEEKING: {
-      if (!mCurrentSeek.Exists()) {
-        // We've received a sample from a previous decode. Discard it.
-        return;
-      }
-      if (audio->mDiscontinuity) {
-        mDropAudioUntilNextDiscontinuity = false;
-      }
-      if (!mDropAudioUntilNextDiscontinuity) {
-        // We must be after the discontinuity; we're receiving samples
-        // at or after the seek target.
-        if (mCurrentSeek.mTarget.IsFast() &&
-            mCurrentSeek.mTarget.GetTime().ToMicroseconds() > mCurrentTimeBeforeSeek &&
-            audio->mTime < mCurrentTimeBeforeSeek) {
-          // We are doing a fastSeek, but we ended up *before* the previous
-          // playback position. This is surprising UX, so switch to an accurate
-          // seek and decode to the seek target. This is not conformant to the
-          // spec, fastSeek should always be fast, but until we get the time to
-          // change all Readers to seek to the keyframe after the currentTime
-          // in this case, we'll just decode forward. Bug 1026330.
-          mCurrentSeek.mTarget.SetType(SeekTarget::Accurate);
-        }
-        if (mCurrentSeek.mTarget.IsFast()) {
-          // Non-precise seek; we can stop the seek at the first sample.
-          Push(audio, MediaData::AUDIO_DATA);
-        } else {
-          // We're doing an accurate seek. We must discard
-          // MediaData up to the one containing exact seek target.
-          if (NS_FAILED(DropAudioUpToSeekTarget(audio))) {
-            DecodeError();
-            return;
-          }
-        }
-      }
-      CheckIfSeekComplete();
-      return;
-    }
     default: {
       // Ignore other cases.
       return;
     }
   }
 }
 
 void
@@ -749,16 +685,18 @@ MediaDecoderStateMachine::OnVideoPopped(
   MaybeStartBuffering();
 }
 
 void
 MediaDecoderStateMachine::OnNotDecoded(MediaData::Type aType,
                                        MediaDecoderReader::NotDecodedReason aReason)
 {
   MOZ_ASSERT(OnTaskQueue());
+  MOZ_ASSERT(mState != DECODER_STATE_SEEKING);
+
   SAMPLE_LOG("OnNotDecoded (aType=%u, aReason=%u)", aType, aReason);
   bool isAudio = aType == MediaData::AUDIO_DATA;
   MOZ_ASSERT_IF(!isAudio, aType == MediaData::VIDEO_DATA);
 
   if (isAudio) {
     mAudioDataRequest.Complete();
   } else {
     mVideoDataRequest.Complete();
@@ -816,25 +754,16 @@ MediaDecoderStateMachine::OnNotDecoded(M
       EnsureVideoDecodeTaskQueued();
     }
     return;
   }
 
   // This is an EOS. Finish off the queue, and then handle things based on our
   // state.
   MOZ_ASSERT(aReason == MediaDecoderReader::END_OF_STREAM);
-  if (!isAudio && mState == DECODER_STATE_SEEKING &&
-      mCurrentSeek.Exists() && mFirstVideoFrameAfterSeek) {
-    // Null sample. Hit end of stream. If we have decoded a frame,
-    // insert it into the queue so that we have something to display.
-    // We make sure to do this before invoking VideoQueue().Finish()
-    // below.
-    Push(mFirstVideoFrameAfterSeek, MediaData::VIDEO_DATA);
-    mFirstVideoFrameAfterSeek = nullptr;
-  }
   if (isAudio) {
     AudioQueue().Finish();
     StopPrerollingAudio();
   } else {
     VideoQueue().Finish();
     StopPrerollingVideo();
   }
   switch (mState) {
@@ -846,31 +775,16 @@ MediaDecoderStateMachine::OnNotDecoded(M
       CheckIfDecodeComplete();
 
       // Schedule next cycle to see if we can leave buffering state.
       if (mState == DECODER_STATE_BUFFERING) {
         ScheduleStateMachine();
       }
       return;
     }
-    case DECODER_STATE_SEEKING: {
-      if (!mCurrentSeek.Exists()) {
-        // We've received a sample from a previous decode. Discard it.
-        return;
-      }
-
-      if (isAudio) {
-        mDropAudioUntilNextDiscontinuity = false;
-      } else {
-        mDropVideoUntilNextDiscontinuity = false;
-      }
-
-      CheckIfSeekComplete();
-      return;
-    }
     default: {
       return;
     }
   }
 }
 
 bool
 MediaDecoderStateMachine::MaybeFinishDecodeFirstFrame()
@@ -892,16 +806,18 @@ MediaDecoderStateMachine::MaybeFinishDec
   return true;
 }
 
 void
 MediaDecoderStateMachine::OnVideoDecoded(MediaData* aVideoSample,
                                          TimeStamp aDecodeStartTime)
 {
   MOZ_ASSERT(OnTaskQueue());
+  MOZ_ASSERT(mState != DECODER_STATE_SEEKING);
+
   RefPtr<MediaData> video(aVideoSample);
   MOZ_ASSERT(video);
   mVideoDataRequest.Complete();
 
   // Handle abnormal or negative timestamps.
   mDecodedVideoEndTime = std::max(mDecodedVideoEndTime, video->GetEndTime());
 
   SAMPLE_LOG("OnVideoDecoded [%lld,%lld] disc=%d",
@@ -944,96 +860,23 @@ MediaDecoderStateMachine::OnVideoDecoded
           std::min(THRESHOLD_FACTOR * DurationToUsecs(decodeTime), mAmpleAudioThresholdUsecs);
         mAmpleAudioThresholdUsecs = std::max(THRESHOLD_FACTOR * mLowAudioThresholdUsecs,
                                               mAmpleAudioThresholdUsecs);
         DECODER_LOG("Slow video decode, set mLowAudioThresholdUsecs=%lld mAmpleAudioThresholdUsecs=%lld",
                     mLowAudioThresholdUsecs, mAmpleAudioThresholdUsecs);
       }
       return;
     }
-    case DECODER_STATE_SEEKING: {
-      if (!mCurrentSeek.Exists()) {
-        // We've received a sample from a previous decode. Discard it.
-        return;
-      }
-      if (mDropVideoUntilNextDiscontinuity) {
-        if (video->mDiscontinuity) {
-          mDropVideoUntilNextDiscontinuity = false;
-        }
-      }
-      if (!mDropVideoUntilNextDiscontinuity) {
-        // We must be after the discontinuity; we're receiving samples
-        // at or after the seek target.
-        if (mCurrentSeek.mTarget.IsFast() &&
-            mCurrentSeek.mTarget.GetTime().ToMicroseconds() > mCurrentTimeBeforeSeek &&
-            video->mTime < mCurrentTimeBeforeSeek) {
-          // We are doing a fastSeek, but we ended up *before* the previous
-          // playback position. This is surprising UX, so switch to an accurate
-          // seek and decode to the seek target. This is not conformant to the
-          // spec, fastSeek should always be fast, but until we get the time to
-          // change all Readers to seek to the keyframe after the currentTime
-          // in this case, we'll just decode forward. Bug 1026330.
-          mCurrentSeek.mTarget.SetType(SeekTarget::Accurate);
-        }
-        if (mCurrentSeek.mTarget.IsFast()) {
-          // Non-precise seek. We can stop the seek at the first sample.
-          Push(video, MediaData::VIDEO_DATA);
-        } else {
-          // We're doing an accurate seek. We still need to discard
-          // MediaData up to the one containing exact seek target.
-          if (NS_FAILED(DropVideoUpToSeekTarget(video))) {
-            DecodeError();
-            return;
-          }
-        }
-      }
-      CheckIfSeekComplete();
-      return;
-    }
     default: {
       // Ignore other cases.
       return;
     }
   }
 }
 
-void
-MediaDecoderStateMachine::CheckIfSeekComplete()
-{
-  MOZ_ASSERT(OnTaskQueue());
-  MOZ_ASSERT(mState == DECODER_STATE_SEEKING);
-
-  const bool videoSeekComplete = IsVideoSeekComplete();
-  if (HasVideo() && !videoSeekComplete) {
-    // We haven't reached the target. Ensure we have requested another sample.
-    if (NS_FAILED(EnsureVideoDecodeTaskQueued())) {
-      DECODER_WARN("Failed to request video during seek");
-      DecodeError();
-    }
-  }
-
-  const bool audioSeekComplete = IsAudioSeekComplete();
-  if (HasAudio() && !audioSeekComplete) {
-    // We haven't reached the target. Ensure we have requested another sample.
-    if (NS_FAILED(EnsureAudioDecodeTaskQueued())) {
-      DECODER_WARN("Failed to request audio during seek");
-      DecodeError();
-    }
-  }
-
-  SAMPLE_LOG("CheckIfSeekComplete() audioSeekComplete=%d videoSeekComplete=%d",
-             audioSeekComplete, videoSeekComplete);
-
-  if (audioSeekComplete && videoSeekComplete) {
-    NS_ASSERTION(AudioQueue().GetSize() <= 1, "Should decode at most one sample");
-    NS_ASSERTION(VideoQueue().GetSize() <= 1, "Should decode at most one sample");
-    SeekCompleted();
-  }
-}
-
 bool
 MediaDecoderStateMachine::IsAudioDecoding()
 {
   MOZ_ASSERT(OnTaskQueue());
   return HasAudio() && !AudioQueue().IsFinished();
 }
 
 bool
@@ -1281,35 +1124,42 @@ MediaDecoderStateMachine::SetDormant(boo
   mPendingDormant.reset();
 
   DECODER_LOG("SetDormant=%d", aDormant);
 
   if (aDormant) {
     if (mState == DECODER_STATE_SEEKING) {
       if (mQueuedSeek.Exists()) {
         // Keep latest seek target
-      } else if (mCurrentSeek.Exists()) {
-        mQueuedSeek = Move(mCurrentSeek);
+      } else if (mSeekTask && mSeekTask->Exists()) {
+        mQueuedSeek = Move(mSeekTask->GetSeekJob());
+        mSeekTaskRequest.DisconnectIfExists();
       } else {
         mQueuedSeek.mTarget = SeekTarget(mCurrentPosition,
                                          SeekTarget::Accurate,
                                          MediaDecoderEventVisibility::Suppressed);
         // XXXbholley - Nobody is listening to this promise. Do we need to pass it
         // back to MediaDecoder when we come out of dormant?
         RefPtr<MediaDecoder::SeekPromise> unused = mQueuedSeek.mPromise.Ensure(__func__);
       }
     } else {
       mQueuedSeek.mTarget = SeekTarget(mCurrentPosition,
                                        SeekTarget::Accurate,
                                        MediaDecoderEventVisibility::Suppressed);
       // XXXbholley - Nobody is listening to this promise. Do we need to pass it
       // back to MediaDecoder when we come out of dormant?
       RefPtr<MediaDecoder::SeekPromise> unused = mQueuedSeek.mPromise.Ensure(__func__);
     }
-    mCurrentSeek.RejectIfExists(__func__);
+
+    // Discard the current seek task.
+    if (mSeekTask) {
+      mSeekTask->Discard();
+      mSeekTask = nullptr;
+    }
+
     SetState(DECODER_STATE_DORMANT);
     if (IsPlaying()) {
       StopPlayback();
     }
 
     Reset();
 
     // Note that we do not wait for the decode task queue to go idle before
@@ -1336,17 +1186,20 @@ MediaDecoderStateMachine::Shutdown()
   // Change state before issuing shutdown request to threads so those
   // threads can start exiting cleanly during the Shutdown call.
   ScheduleStateMachine();
   SetState(DECODER_STATE_SHUTDOWN);
 
   mBufferedUpdateRequest.DisconnectIfExists();
 
   mQueuedSeek.RejectIfExists(__func__);
-  mCurrentSeek.RejectIfExists(__func__);
+  if (mSeekTask) {
+    mSeekTask->Discard();
+    mSeekTask = nullptr;
+  }
 
 #ifdef MOZ_EME
   mCDMProxyPromise.DisconnectIfExists();
 #endif
 
   if (IsPlaying()) {
     StopPlayback();
   }
@@ -1525,17 +1378,17 @@ MediaDecoderStateMachine::Seek(SeekTarge
   mQueuedSeek.RejectIfExists(__func__);
 
   DECODER_LOG("Changed state to SEEKING (to %lld)", aTarget.GetTime().ToMicroseconds());
   SetState(DECODER_STATE_SEEKING);
 
   SeekJob seekJob;
   seekJob.mTarget = aTarget;
   InitiateSeek(Move(seekJob));
-  return mCurrentSeek.mPromise.Ensure(__func__);
+  return mSeekTask->GetSeekJob().mPromise.Ensure(__func__);
 }
 
 RefPtr<MediaDecoder::SeekPromise>
 MediaDecoderStateMachine::InvokeSeek(SeekTarget aTarget)
 {
   return InvokeAsync(OwnerThread(), this, __func__,
                      &MediaDecoderStateMachine::Seek, aTarget);
 }
@@ -1609,60 +1462,116 @@ MediaDecoderStateMachine::DispatchDecode
   }
 }
 
 void
 MediaDecoderStateMachine::InitiateSeek(SeekJob aSeekJob)
 {
   MOZ_ASSERT(OnTaskQueue());
 
-  mCurrentSeek.RejectIfExists(__func__);
-  mCurrentSeek = Move(aSeekJob);
-
-  // Bound the seek time to be inside the media range.
-  int64_t end = Duration().ToMicroseconds();
-  NS_ASSERTION(end != -1, "Should know end time by now");
-  int64_t seekTime = mCurrentSeek.mTarget.GetTime().ToMicroseconds();
-  seekTime = std::min(seekTime, end);
-  seekTime = std::max(int64_t(0), seekTime);
-  NS_ASSERTION(seekTime >= 0 && seekTime <= end,
-               "Can only seek in range [0,duration]");
-  mCurrentSeek.mTarget.SetTime(media::TimeUnit::FromMicroseconds(seekTime));
-
-  mDropAudioUntilNextDiscontinuity = HasAudio();
-  mDropVideoUntilNextDiscontinuity = HasVideo();
-  mCurrentTimeBeforeSeek = GetMediaTime();
+  // Discard the existing seek task.
+  if (mSeekTask) {
+    mSeekTask->Discard();
+  }
+
+  mSeekTaskRequest.DisconnectIfExists();
+
+  // Create a new SeekTask instance for the incoming seek task.
+  mSeekTask = SeekTask::CreateSeekTask(mDecoderID, OwnerThread(), mReader.get(),
+                                       mReaderWrapper.get(), Move(aSeekJob),
+                                       mInfo, Duration(), GetMediaTime());
 
   // Stop playback now to ensure that while we're outside the monitor
   // dispatching SeekingStarted, playback doesn't advance and mess with
   // mCurrentPosition that we've setting to seekTime here.
   StopPlayback();
-  UpdatePlaybackPositionInternal(mCurrentSeek.mTarget.GetTime().ToMicroseconds());
-
-  mOnSeekingStart.Notify(mCurrentSeek.mTarget.mEventVisibility);
+  UpdatePlaybackPositionInternal(mSeekTask->GetSeekJob().mTarget.GetTime().ToMicroseconds());
+
+  mOnSeekingStart.Notify(mSeekTask->GetSeekJob().mTarget.mEventVisibility);
 
   // Reset our state machine and decoding pipeline before seeking.
-  Reset();
+  if (mSeekTask->NeedToResetMDSM()) { Reset(); }
 
   // Do the seek.
-  RefPtr<MediaDecoderStateMachine> self = this;
-  mSeekRequest.Begin(
-    mReaderWrapper->Seek(mCurrentSeek.mTarget, Duration())
-    ->Then(OwnerThread(), __func__,
-           [self] (media::TimeUnit) -> void {
-             self->mSeekRequest.Complete();
-             // We must decode the first samples of active streams, so we can determine
-             // the new stream time. So dispatch tasks to do that.
-             self->EnsureAudioDecodeTaskQueued();
-             self->EnsureVideoDecodeTaskQueued();
-           }, [self] (nsresult aResult) -> void {
-             self->mSeekRequest.Complete();
-             MOZ_ASSERT(NS_FAILED(aResult), "Cancels should also disconnect mSeekRequest");
-             self->DecodeError();
-           }));
+  mSeekTaskRequest.Begin(mSeekTask->Seek(Duration())
+    ->Then(OwnerThread(), __func__, this,
+           &MediaDecoderStateMachine::OnSeekTaskResolved,
+           &MediaDecoderStateMachine::OnSeekTaskRejected));
+}
+
+void
+MediaDecoderStateMachine::OnSeekTaskResolved(SeekTaskResolveValue aValue)
+{
+  MOZ_ASSERT(OnTaskQueue());
+
+  mSeekTaskRequest.Complete();
+
+  if (aValue.mSeekedAudioData) {
+    Push(aValue.mSeekedAudioData.get(), MediaData::AUDIO_DATA);
+    mDecodedAudioEndTime =
+      std::max(aValue.mSeekedAudioData->GetEndTime(), mDecodedAudioEndTime);
+  }
+
+  if (aValue.mSeekedVideoData) {
+    Push(aValue.mSeekedVideoData.get(), MediaData::VIDEO_DATA);
+    mDecodedVideoEndTime =
+      std::max(aValue.mSeekedVideoData->GetEndTime(), mDecodedVideoEndTime);
+  }
+
+  if (aValue.mIsAudioQueueFinished) {
+    AudioQueue().Finish();
+    StopPrerollingAudio();
+  }
+
+  if (aValue.mIsVideoQueueFinished) {
+    VideoQueue().Finish();
+    StopPrerollingVideo();
+  }
+
+  if (aValue.mNeedToStopPrerollingAudio) {
+    StopPrerollingAudio();
+  }
+
+  if (aValue.mNeedToStopPrerollingVideo) {
+    StopPrerollingVideo();
+  }
+
+  SeekCompleted();
+
+  mSeekTask = nullptr;
+}
+
+void
+MediaDecoderStateMachine::OnSeekTaskRejected(SeekTaskRejectValue aValue)
+{
+  MOZ_ASSERT(OnTaskQueue());
+
+  mSeekTaskRequest.Complete();
+
+  if (aValue.mIsAudioQueueFinished) {
+    AudioQueue().Finish();
+    StopPrerollingAudio();
+  }
+
+  if (aValue.mIsVideoQueueFinished) {
+    VideoQueue().Finish();
+    StopPrerollingVideo();
+  }
+
+  if (aValue.mNeedToStopPrerollingAudio) {
+    StopPrerollingAudio();
+  }
+
+  if (aValue.mNeedToStopPrerollingVideo) {
+    StopPrerollingVideo();
+  }
+
+  DecodeError();
+
+  mSeekTask = nullptr;
 }
 
 nsresult
 MediaDecoderStateMachine::DispatchAudioDecodeTaskIfNeeded()
 {
   MOZ_ASSERT(OnTaskQueue());
 
   if (IsShutdown()) {
@@ -1675,28 +1584,28 @@ MediaDecoderStateMachine::DispatchAudioD
 
   return NS_OK;
 }
 
 nsresult
 MediaDecoderStateMachine::EnsureAudioDecodeTaskQueued()
 {
   MOZ_ASSERT(OnTaskQueue());
+  MOZ_ASSERT(mState != DECODER_STATE_SEEKING);
 
   SAMPLE_LOG("EnsureAudioDecodeTaskQueued isDecoding=%d status=%s",
               IsAudioDecoding(), AudioRequestStatus());
 
   if (mState != DECODER_STATE_DECODING &&
-      mState != DECODER_STATE_BUFFERING &&
-      mState != DECODER_STATE_SEEKING) {
+      mState != DECODER_STATE_BUFFERING) {
     return NS_OK;
   }
 
   if (!IsAudioDecoding() || mAudioDataRequest.Exists() ||
-      mAudioWaitRequest.Exists() || mSeekRequest.Exists()) {
+      mAudioWaitRequest.Exists()) {
     return NS_OK;
   }
 
   RequestAudioData();
   return NS_OK;
 }
 
 void
@@ -1729,28 +1638,28 @@ MediaDecoderStateMachine::DispatchVideoD
 
   return NS_OK;
 }
 
 nsresult
 MediaDecoderStateMachine::EnsureVideoDecodeTaskQueued()
 {
   MOZ_ASSERT(OnTaskQueue());
+  MOZ_ASSERT(mState != DECODER_STATE_SEEKING);
 
   SAMPLE_LOG("EnsureVideoDecodeTaskQueued isDecoding=%d status=%s",
              IsVideoDecoding(), VideoRequestStatus());
 
   if (mState != DECODER_STATE_DECODING &&
-      mState != DECODER_STATE_BUFFERING &&
-      mState != DECODER_STATE_SEEKING) {
+      mState != DECODER_STATE_BUFFERING) {
     return NS_OK;
   }
 
   if (!IsVideoDecoding() || mVideoDataRequest.Exists() ||
-      mVideoWaitRequest.Exists() || mSeekRequest.Exists()) {
+      mVideoWaitRequest.Exists()) {
     return NS_OK;
   }
 
   RequestVideoData();
   return NS_OK;
 }
 
 void
@@ -2051,17 +1960,17 @@ MediaDecoderStateMachine::FinishDecodeFi
 }
 
 void
 MediaDecoderStateMachine::SeekCompleted()
 {
   MOZ_ASSERT(OnTaskQueue());
   MOZ_ASSERT(mState == DECODER_STATE_SEEKING);
 
-  int64_t seekTime = mCurrentSeek.mTarget.GetTime().ToMicroseconds();
+  int64_t seekTime = mSeekTask->GetSeekJob().mTarget.GetTime().ToMicroseconds();
   int64_t newCurrentTime = seekTime;
 
   // Setup timestamp state.
   RefPtr<MediaData> video = VideoQueue().PeekFront();
   if (seekTime == Duration().ToMicroseconds()) {
     newCurrentTime = seekTime;
   } else if (HasAudio()) {
     MediaData* audio = AudioQueue().PeekFront();
@@ -2096,17 +2005,17 @@ MediaDecoderStateMachine::SeekCompleted(
     nextState = DECODER_STATE_COMPLETED;
   } else {
     DECODER_LOG("Changed state from SEEKING (to %lld) to DECODING", seekTime);
     nextState = DECODER_STATE_DECODING;
   }
 
   // We want to resolve the seek request prior finishing the first frame
   // to ensure that the seeked event is fired prior loadeded.
-  mCurrentSeek.Resolve(nextState == DECODER_STATE_COMPLETED, __func__);
+  mSeekTask->GetSeekJob().Resolve(nextState == DECODER_STATE_COMPLETED, __func__);
 
   if (mDecodingFirstFrame) {
     // We were resuming from dormant, or initiated a seek early.
     // We can fire loadeddata now.
     FinishDecodeFirstFrame();
   }
 
   if (nextState == DECODER_STATE_DECODING) {
@@ -2346,26 +2255,23 @@ MediaDecoderStateMachine::Reset()
   StopMediaSink();
 
   mDecodedVideoEndTime = 0;
   mDecodedAudioEndTime = 0;
   mAudioCompleted = false;
   mVideoCompleted = false;
   AudioQueue().Reset();
   VideoQueue().Reset();
-  mFirstVideoFrameAfterSeek = nullptr;
-  mDropAudioUntilNextDiscontinuity = true;
-  mDropVideoUntilNextDiscontinuity = true;
 
   mMetadataRequest.DisconnectIfExists();
   mAudioDataRequest.DisconnectIfExists();
   mAudioWaitRequest.DisconnectIfExists();
   mVideoDataRequest.DisconnectIfExists();
   mVideoWaitRequest.DisconnectIfExists();
-  mSeekRequest.DisconnectIfExists();
+  mSeekTaskRequest.DisconnectIfExists();
 
   mPlaybackOffset = 0;
 
   nsCOMPtr<nsIRunnable> resetTask =
     NS_NewRunnableMethod(mReader, &MediaDecoderReader::ResetDecode);
   DecodeTaskQueue()->Dispatch(resetTask.forget());
 }
 
@@ -2414,129 +2320,16 @@ MediaDecoderStateMachine::UpdatePlayback
   // Otherwise, MediaDecoder::AddOutputStream could kick in when we are outside
   // the monitor and get a staled value from GetCurrentTimeUs() which hits the
   // assertion in GetClock().
 
   int64_t delay = std::max<int64_t>(1, AUDIO_DURATION_USECS / mPlaybackRate);
   ScheduleStateMachineIn(delay);
 }
 
-nsresult
-MediaDecoderStateMachine::DropVideoUpToSeekTarget(MediaData* aSample)
-{
-  MOZ_ASSERT(OnTaskQueue());
-  RefPtr<VideoData> video(aSample->As<VideoData>());
-  MOZ_ASSERT(video);
-  DECODER_LOG("DropVideoUpToSeekTarget() frame [%lld, %lld]",
-              video->mTime, video->GetEndTime());
-  MOZ_ASSERT(mCurrentSeek.Exists());
-  const int64_t target = mCurrentSeek.mTarget.GetTime().ToMicroseconds();
-
-  // If the frame end time is less than the seek target, we won't want
-  // to display this frame after the seek, so discard it.
-  if (target >= video->GetEndTime()) {
-    DECODER_LOG("DropVideoUpToSeekTarget() pop video frame [%lld, %lld] target=%lld",
-                video->mTime, video->GetEndTime(), target);
-    mFirstVideoFrameAfterSeek = video;
-  } else {
-    if (target >= video->mTime && video->GetEndTime() >= target) {
-      // The seek target lies inside this frame's time slice. Adjust the frame's
-      // start time to match the seek target. We do this by replacing the
-      // first frame with a shallow copy which has the new timestamp.
-      RefPtr<VideoData> temp = VideoData::ShallowCopyUpdateTimestamp(video, target);
-      video = temp;
-    }
-    mFirstVideoFrameAfterSeek = nullptr;
-
-    DECODER_LOG("DropVideoUpToSeekTarget() found video frame [%lld, %lld] containing target=%lld",
-                video->mTime, video->GetEndTime(), target);
-
-    MOZ_ASSERT(VideoQueue().GetSize() == 0, "Should be the 1st sample after seeking");
-    Push(video, MediaData::VIDEO_DATA);
-  }
-
-  return NS_OK;
-}
-
-nsresult
-MediaDecoderStateMachine::DropAudioUpToSeekTarget(MediaData* aSample)
-{
-  MOZ_ASSERT(OnTaskQueue());
-  RefPtr<AudioData> audio(aSample->As<AudioData>());
-  MOZ_ASSERT(audio &&
-             mCurrentSeek.Exists() &&
-             mCurrentSeek.mTarget.IsAccurate());
-
-  CheckedInt64 sampleDuration =
-    FramesToUsecs(audio->mFrames, mInfo.mAudio.mRate);
-  if (!sampleDuration.isValid()) {
-    return NS_ERROR_FAILURE;
-  }
-
-  if (audio->mTime + sampleDuration.value() <= mCurrentSeek.mTarget.GetTime().ToMicroseconds()) {
-    // Our seek target lies after the frames in this AudioData. Don't
-    // push it onto the audio queue, and keep decoding forwards.
-    return NS_OK;
-  }
-
-  if (audio->mTime > mCurrentSeek.mTarget.GetTime().ToMicroseconds()) {
-    // The seek target doesn't lie in the audio block just after the last
-    // audio frames we've seen which were before the seek target. This
-    // could have been the first audio data we've seen after seek, i.e. the
-    // seek terminated after the seek target in the audio stream. Just
-    // abort the audio decode-to-target, the state machine will play
-    // silence to cover the gap. Typically this happens in poorly muxed
-    // files.
-    DECODER_WARN("Audio not synced after seek, maybe a poorly muxed file?");
-    Push(audio, MediaData::AUDIO_DATA);
-    return NS_OK;
-  }
-
-  // The seek target lies somewhere in this AudioData's frames, strip off
-  // any frames which lie before the seek target, so we'll begin playback
-  // exactly at the seek target.
-  NS_ASSERTION(mCurrentSeek.mTarget.GetTime().ToMicroseconds() >= audio->mTime,
-               "Target must at or be after data start.");
-  NS_ASSERTION(mCurrentSeek.mTarget.GetTime().ToMicroseconds() < audio->mTime + sampleDuration.value(),
-               "Data must end after target.");
-
-  CheckedInt64 framesToPrune =
-    UsecsToFrames(mCurrentSeek.mTarget.GetTime().ToMicroseconds() - audio->mTime, mInfo.mAudio.mRate);
-  if (!framesToPrune.isValid()) {
-    return NS_ERROR_FAILURE;
-  }
-  if (framesToPrune.value() > audio->mFrames) {
-    // We've messed up somehow. Don't try to trim frames, the |frames|
-    // variable below will overflow.
-    DECODER_WARN("Can't prune more frames that we have!");
-    return NS_ERROR_FAILURE;
-  }
-  uint32_t frames = audio->mFrames - static_cast<uint32_t>(framesToPrune.value());
-  uint32_t channels = audio->mChannels;
-  auto audioData = MakeUnique<AudioDataValue[]>(frames * channels);
-  memcpy(audioData.get(),
-         audio->mAudioData.get() + (framesToPrune.value() * channels),
-         frames * channels * sizeof(AudioDataValue));
-  CheckedInt64 duration = FramesToUsecs(frames, mInfo.mAudio.mRate);
-  if (!duration.isValid()) {
-    return NS_ERROR_FAILURE;
-  }
-  RefPtr<AudioData> data(new AudioData(audio->mOffset,
-                                       mCurrentSeek.mTarget.GetTime().ToMicroseconds(),
-                                       duration.value(),
-                                       frames,
-                                       Move(audioData),
-                                       channels,
-                                       audio->mRate));
-  MOZ_ASSERT(AudioQueue().GetSize() == 0, "Should be the 1st sample after seeking");
-  Push(data, MediaData::AUDIO_DATA);
-
-  return NS_OK;
-}
-
 void MediaDecoderStateMachine::UpdateNextFrameStatus()
 {
   MOZ_ASSERT(OnTaskQueue());
 
   MediaDecoderOwner::NextFrameStatus status;
   const char* statusString;
   if (mState <= DECODER_STATE_WAIT_FOR_CDM || IsDecodingFirstFrame()) {
     status = MediaDecoderOwner::NEXT_FRAME_UNAVAILABLE;

--- a/dom/media/MediaDecoderStateMachine.h
+++ b/dom/media/MediaDecoderStateMachine.h
@@ -439,19 +439,16 @@ protected:
 
   // Return the current time, either the audio clock if available (if the media
   // has audio, and the playback is possible), or a clock for the video.
   // Called on the state machine thread.
   // If aTimeStamp is non-null, set *aTimeStamp to the TimeStamp corresponding
   // to the returned stream time.
   int64_t GetClock(TimeStamp* aTimeStamp = nullptr) const;
 
-  nsresult DropAudioUpToSeekTarget(MediaData* aSample);
-  nsresult DropVideoUpToSeekTarget(MediaData* aSample);
-
   void SetStartTime(int64_t aStartTimeUsecs);
 
   // Update only the state machine's current playback position (and duration,
   // if unknown).  Does not update the playback position on the decoder or
   // media element -- use UpdatePlaybackPosition for that.  Called on the state
   // machine thread, caller must hold the decoder lock.
   void UpdatePlaybackPositionInternal(int64_t aTime);
 
@@ -575,24 +572,16 @@ protected:
   // If so will trigger firing loadeddata event.
   // If there are any queued seek, will change state to DECODER_STATE_SEEKING
   // and return true.
   bool MaybeFinishDecodeFirstFrame();
   // Return true if we are currently decoding the first frames.
   bool IsDecodingFirstFrame();
   void FinishDecodeFirstFrame();
 
-  // Seeks to mSeekTarget. Called on the decode thread. The decoder monitor
-  // must be held with exactly one lock count.
-  void DecodeSeek();
-
-  void CheckIfSeekComplete();
-  bool IsAudioSeekComplete();
-  bool IsVideoSeekComplete();
-
   // Completes the seek operation, moves onto the next appropriate state.
   void SeekCompleted();
 
   // Queries our state to see whether the decode has finished for all streams.
   // If so, we move into DECODER_STATE_COMPLETED and schedule the state machine
   // to run.
   // The decoder monitor must be held.
   void CheckIfDecodeComplete();
@@ -693,18 +682,22 @@ private:
     MOZ_ASSERT(OnTaskQueue());
     return mPlayState == MediaDecoder::PLAY_STATE_PLAYING ||
            mNextPlayState == MediaDecoder::PLAY_STATE_PLAYING;
   }
 
   // Queued seek - moves to mCurrentSeek when DecodeFirstFrame completes.
   SeekJob mQueuedSeek;
 
-  // The position that we're currently seeking to.
-  SeekJob mCurrentSeek;
+  // mSeekTask is responsible for executing the current seek request.
+  RefPtr<media::SeekTask> mSeekTask;
+  MozPromiseRequestHolder<media::SeekTask::SeekTaskPromise> mSeekTaskRequest;
+
+  void OnSeekTaskResolved(media::SeekTaskResolveValue aValue);
+  void OnSeekTaskRejected(media::SeekTaskRejectValue aValue);
 
   // Media Fragment end time in microseconds. Access controlled by decoder monitor.
   int64_t mFragmentEndTime;
 
   // The media sink resource.  Used on the state machine thread.
   RefPtr<media::MediaSink> mMediaSink;
 
   // The reader, don't call its methods with the decoder monitor held.
@@ -814,22 +807,16 @@ private:
   {
     MOZ_ASSERT(OnTaskQueue());
     if (mIsVideoPrerolling) {
       mIsVideoPrerolling = false;
       ScheduleStateMachine();
     }
   }
 
-  // This temporarily stores the first frame we decode after we seek.
-  // This is so that if we hit end of stream while we're decoding to reach
-  // the seek target, we will still have a frame that we can display as the
-  // last frame in the media.
-  RefPtr<MediaData> mFirstVideoFrameAfterSeek;
-
   // When we start decoding (either for the first time, or after a pause)
   // we may be low on decoded data. We don't want our "low data" logic to
   // kick in and decide that we're low on decoded data because the download
   // can't keep up with the decode, and cause us to pause playback. So we
   // have a "preroll" stage, where we ignore the results of our "low data"
   // logic during the first few frames of our decode. This occurs during
   // playback. The flags below are true when the corresponding stream is
   // being "prerolled".
@@ -925,31 +912,16 @@ private:
   // memory and CPU overhead.
   bool mMinimizePreroll;
 
   // True if the decode thread has gone filled its buffers and is now
   // waiting to be awakened before it continues decoding. Synchronized
   // by the decoder monitor.
   bool mDecodeThreadWaiting;
 
-  // These two flags are true when we need to drop decoded samples that
-  // we receive up to the next discontinuity. We do this when we seek;
-  // the first sample in each stream after the seek is marked as being
-  // a "discontinuity".
-  bool mDropAudioUntilNextDiscontinuity;
-  bool mDropVideoUntilNextDiscontinuity;
-
-  // Track the current seek promise made by the reader.
-  MozPromiseRequestHolder<MediaDecoderReader::SeekPromise> mSeekRequest;
-
-  // We record the playback position before we seek in order to
-  // determine where the seek terminated relative to the playback position
-  // we were at before the seek.
-  int64_t mCurrentTimeBeforeSeek;
-
   // Track our request for metadata from the reader.
   MozPromiseRequestHolder<MediaDecoderReader::MetadataPromise> mMetadataRequest;
 
   // Stores presentation info required for playback. The decoder monitor
   // must be held when accessing this.
   MediaInfo mInfo;
 
   nsAutoPtr<MetadataTags> mMetadataTags;