--- a/dom/media/MediaFormatReader.cpp
+++ b/dom/media/MediaFormatReader.cpp
@@ -57,19 +57,19 @@ TrackTypeToStr(TrackInfo::TrackType aTra
   }
 }
 
 MediaFormatReader::MediaFormatReader(AbstractMediaDecoder* aDecoder,
                                      MediaDataDemuxer* aDemuxer,
                                      VideoFrameContainer* aVideoFrameContainer,
                                      layers::LayersBackend aLayersBackend)
   : MediaDecoderReader(aDecoder)
-  , mAudio(this, MediaData::AUDIO_DATA, Preferences::GetUint("media.audio-decode-ahead", 2),
+  , mAudio(this, MediaData::AUDIO_DATA,
            Preferences::GetUint("media.audio-max-decode-error", 3))
-  , mVideo(this, MediaData::VIDEO_DATA, Preferences::GetUint("media.video-decode-ahead", 2),
+  , mVideo(this, MediaData::VIDEO_DATA,
            Preferences::GetUint("media.video-max-decode-error", 2))
   , mDemuxer(aDemuxer)
   , mDemuxerInitDone(false)
   , mLastReportedNumDecodedFrames(0)
   , mPreviousDecodedKeyframeTime_us(sNoPreviousDecodedKeyframe)
   , mLayersBackendType(aLayersBackend)
   , mInitDone(false)
   , mIsEncrypted(false)
@@ -557,17 +557,17 @@ MediaFormatReader::RequestVideoData(bool
   if (!mVideo.HasInternalSeekPending() &&
       ShouldSkip(aSkipToNextKeyframe, timeThreshold)) {
     RefPtr<MediaDataPromise> p = mVideo.EnsurePromise(__func__);
     SkipVideoDemuxToNextKeyFrame(timeThreshold);
     return p;
   }
 
   RefPtr<MediaDataPromise> p = mVideo.EnsurePromise(__func__);
-  NotifyDecodingRequested(TrackInfo::kVideoTrack);
+  ScheduleUpdate(TrackInfo::kVideoTrack);
 
   return p;
 }
 
 void
 MediaFormatReader::OnDemuxFailed(TrackType aTrack, DemuxerFailureReason aFailure)
 {
   MOZ_ASSERT(OnTaskQueue());
@@ -601,17 +601,16 @@ MediaFormatReader::OnDemuxFailed(TrackTy
       MOZ_ASSERT(false);
       break;
   }
 }
 
 void
 MediaFormatReader::DoDemuxVideo()
 {
-  // TODO Use DecodeAhead value rather than 1.
   mVideo.mDemuxRequest.Begin(mVideo.mTrackDemuxer->GetSamples(1)
                       ->Then(OwnerThread(), __func__, this,
                              &MediaFormatReader::OnVideoDemuxCompleted,
                              &MediaFormatReader::OnVideoDemuxFailed));
 }
 
 void
 MediaFormatReader::OnVideoDemuxCompleted(RefPtr<MediaTrackDemuxer::SamplesHolder> aSamples)
@@ -652,25 +651,24 @@ MediaFormatReader::RequestAudioData()
   }
 
   if (mShutdown) {
     NS_WARNING("RequestAudioData on shutdown MediaFormatReader!");
     return MediaDataPromise::CreateAndReject(CANCELED, __func__);
   }
 
   RefPtr<MediaDataPromise> p = mAudio.EnsurePromise(__func__);
-  NotifyDecodingRequested(TrackInfo::kAudioTrack);
+  ScheduleUpdate(TrackInfo::kAudioTrack);
 
   return p;
 }
 
 void
 MediaFormatReader::DoDemuxAudio()
 {
-  // TODO Use DecodeAhead value rather than 1.
   mAudio.mDemuxRequest.Begin(mAudio.mTrackDemuxer->GetSamples(1)
                       ->Then(OwnerThread(), __func__, this,
                              &MediaFormatReader::OnAudioDemuxCompleted,
                              &MediaFormatReader::OnAudioDemuxFailed));
 }
 
 void
 MediaFormatReader::OnAudioDemuxCompleted(RefPtr<MediaTrackDemuxer::SamplesHolder> aSamples)
@@ -692,26 +690,27 @@ MediaFormatReader::NotifyNewOutput(Track
   auto& decoder = GetDecoderData(aTrack);
   if (!decoder.mOutputRequested) {
     LOG("MediaFormatReader produced output while flushing, discarding.");
     return;
   }
   decoder.mOutput.AppendElement(aSample);
   decoder.mNumSamplesOutput++;
   decoder.mNumOfConsecutiveError = 0;
+  decoder.mDecodePending = false;
   ScheduleUpdate(aTrack);
 }
 
 void
 MediaFormatReader::NotifyInputExhausted(TrackType aTrack)
 {
   MOZ_ASSERT(OnTaskQueue());
   LOGV("Decoder has requested more %s data", TrackTypeToStr(aTrack));
   auto& decoder = GetDecoderData(aTrack);
-  decoder.mInputExhausted = true;
+  decoder.mDecodePending = false;
   ScheduleUpdate(aTrack);
 }
 
 void
 MediaFormatReader::NotifyDrainComplete(TrackType aTrack)
 {
   MOZ_ASSERT(OnTaskQueue());
   auto& decoder = GetDecoderData(aTrack);
@@ -750,43 +749,31 @@ void
 MediaFormatReader::NotifyEndOfStream(TrackType aTrack)
 {
   MOZ_ASSERT(OnTaskQueue());
   auto& decoder = GetDecoderData(aTrack);
   decoder.mDemuxEOS = true;
   ScheduleUpdate(aTrack);
 }
 
-void
-MediaFormatReader::NotifyDecodingRequested(TrackType aTrack)
-{
-  MOZ_ASSERT(OnTaskQueue());
-  auto& decoder = GetDecoderData(aTrack);
-  decoder.mDecodingRequested = true;
-  ScheduleUpdate(aTrack);
-}
-
 bool
 MediaFormatReader::NeedInput(DecoderData& aDecoder)
 {
-  // We try to keep a few more compressed samples input than decoded samples
-  // have been output, provided the state machine has requested we send it a
-  // decoded sample. To account for H.264 streams which may require a longer
-  // run of input than we input, decoders fire an "input exhausted" callback,
-  // which overrides our "few more samples" threshold.
+  // To account for H.264 streams which may require a longer
+  // run of input than we input, decoders fire an "input exhausted" callback.
+  // The decoder will not be fed a new raw sample until either Output callback
+  // has been called, or InputExhausted was called.
   return
+    (aDecoder.HasPromise() || aDecoder.mTimeThreshold.isSome()) &&
     !aDecoder.HasPendingDrain() &&
     !aDecoder.HasFatalError() &&
-    aDecoder.mDecodingRequested &&
     !aDecoder.mDemuxRequest.Exists() &&
+    !aDecoder.mOutput.Length() &&
     !aDecoder.HasInternalSeekPending() &&
-    aDecoder.mOutput.Length() <= aDecoder.mDecodeAhead &&
-    (aDecoder.mInputExhausted || !aDecoder.mQueuedSamples.IsEmpty() ||
-     aDecoder.mTimeThreshold.isSome() ||
-     aDecoder.mNumSamplesInput - aDecoder.mNumSamplesOutput <= aDecoder.mDecodeAhead);
+    !aDecoder.mDecodePending;
 }
 
 void
 MediaFormatReader::ScheduleUpdate(TrackType aTrack)
 {
   MOZ_ASSERT(OnTaskQueue());
   if (mShutdown) {
     return;
@@ -927,16 +914,17 @@ MediaFormatReader::DecodeDemuxedSamples(
                                         MediaRawData* aSample)
 {
   MOZ_ASSERT(OnTaskQueue());
   auto& decoder = GetDecoderData(aTrack);
   if (NS_FAILED(decoder.mDecoder->Input(aSample))) {
       LOG("Unable to pass frame to decoder");
       return false;
   }
+  decoder.mDecodePending = true;
   return true;
 }
 
 void
 MediaFormatReader::HandleDemuxedSamples(TrackType aTrack,
                                         AbstractMediaDecoder::AutoNotifyDecoded& aA)
 {
   MOZ_ASSERT(OnTaskQueue());
@@ -1002,17 +990,17 @@ MediaFormatReader::HandleDemuxedSamples(
       decoder.mLastStreamSourceID = info->GetID();
       decoder.mNextStreamSourceID.reset();
       // Reset will clear our array of queued samples. So make a copy now.
       nsTArray<RefPtr<MediaRawData>> samples{decoder.mQueuedSamples};
       Reset(aTrack);
       decoder.ShutdownDecoder();
       if (sample->mKeyframe) {
         decoder.mQueuedSamples.AppendElements(Move(samples));
-        NotifyDecodingRequested(aTrack);
+        ScheduleUpdate(aTrack);
       } else {
         TimeInterval time =
           TimeInterval(TimeUnit::FromMicroseconds(sample->mTime),
                        TimeUnit::FromMicroseconds(sample->GetEndTime()));
         InternalSeekTarget seekTarget =
           decoder.mTimeThreshold.refOr(InternalSeekTarget(time, false));
         LOG("Stream change occurred on a non-keyframe. Seeking to:%lld",
             sample->mTime);
@@ -1040,19 +1028,16 @@ MediaFormatReader::HandleDemuxedSamples(
     decoder.mQueuedSamples.RemoveElementAt(0);
     if (mDemuxOnly) {
       // If demuxed-only case, ReturnOutput will resolve with one demuxed data.
       // Then we should stop doing the iteration.
       return;
     }
     samplesPending = true;
   }
-
-  // We have serviced the decoder's request for more data.
-  decoder.mInputExhausted = false;
 }
 
 void
 MediaFormatReader::InternalSeek(TrackType aTrack, const InternalSeekTarget& aTarget)
 {
   MOZ_ASSERT(OnTaskQueue());
   LOG("%s internal seek to %f",
       TrackTypeToStr(aTrack), aTarget.Time().ToSeconds());
@@ -1066,17 +1051,17 @@ MediaFormatReader::InternalSeek(TrackTyp
              ->Then(OwnerThread(), __func__,
                     [self, aTrack] (media::TimeUnit aTime) {
                       auto& decoder = self->GetDecoderData(aTrack);
                       decoder.mSeekRequest.Complete();
                       MOZ_ASSERT(decoder.mTimeThreshold,
                                  "Seek promise must be disconnected when timethreshold is reset");
                       decoder.mTimeThreshold.ref().mHasSeeked = true;
                       self->SetVideoDecodeThreshold();
-                      self->NotifyDecodingRequested(aTrack);
+                      self->ScheduleUpdate(aTrack);
                     },
                     [self, aTrack] (DemuxerFailureReason aResult) {
                       auto& decoder = self->GetDecoderData(aTrack);
                       decoder.mSeekRequest.Complete();
                       switch (aResult) {
                         case DemuxerFailureReason::WAITING_FOR_DATA:
                           self->NotifyWaitingForData(aTrack);
                           break;
@@ -1270,16 +1255,17 @@ MediaFormatReader::Update(TrackType aTra
 
   if (decoder.mNeedDraining) {
     DrainDecoder(aTrack);
     return;
   }
 
   if (decoder.mError &&
       decoder.mError.ref() == MediaDataDecoderError::DECODE_ERROR) {
+    decoder.mDecodePending = false;
     decoder.mError.reset();
     if (++decoder.mNumOfConsecutiveError > decoder.mMaxConsecutiveError) {
       NotifyError(aTrack);
       return;
     }
     LOG("%s decoded error count %d", TrackTypeToStr(aTrack),
                                      decoder.mNumOfConsecutiveError);
     media::TimeUnit nextKeyframe;
@@ -1287,21 +1273,21 @@ MediaFormatReader::Update(TrackType aTra
         NS_SUCCEEDED(decoder.mTrackDemuxer->GetNextRandomAccessPoint(&nextKeyframe))) {
       SkipVideoDemuxToNextKeyFrame(decoder.mLastSampleTime.refOr(TimeInterval()).Length());
       return;
     }
   }
 
   bool needInput = NeedInput(decoder);
 
-  LOGV("Update(%s) ni=%d no=%d ie=%d, in:%llu out:%llu qs=%u pending:%u waiting:%d ahead:%d sid:%u",
-       TrackTypeToStr(aTrack), needInput, needOutput, decoder.mInputExhausted,
+  LOGV("Update(%s) ni=%d no=%d ie=%d, in:%llu out:%llu qs=%u pending:%u waiting:%d promise:%d sid:%u",
+       TrackTypeToStr(aTrack), needInput, needOutput, decoder.mDecodePending,
        decoder.mNumSamplesInput, decoder.mNumSamplesOutput,
        uint32_t(size_t(decoder.mSizeOfQueue)), uint32_t(decoder.mOutput.Length()),
-       decoder.mWaitingForData, !decoder.HasPromise(), decoder.mLastStreamSourceID);
+       decoder.mWaitingForData, decoder.HasPromise(), decoder.mLastStreamSourceID);
 
   if (decoder.mWaitingForData &&
       (!decoder.mTimeThreshold || decoder.mTimeThreshold.ref().mWaiting)) {
     // Nothing more we can do at present.
     LOGV("Still waiting for data.");
     return;
   }
 
@@ -1579,17 +1565,17 @@ void
 MediaFormatReader::OnVideoSkipCompleted(uint32_t aSkipped)
 {
   MOZ_ASSERT(OnTaskQueue());
   LOG("Skipping succeeded, skipped %u frames", aSkipped);
   mSkipRequest.Complete();
 
   VideoSkipReset(aSkipped);
 
-  NotifyDecodingRequested(TrackInfo::kVideoTrack);
+  ScheduleUpdate(TrackInfo::kVideoTrack);
 }
 
 void
 MediaFormatReader::OnVideoSkipFailed(MediaTrackDemuxer::SkipFailureHolder aFailure)
 {
   MOZ_ASSERT(OnTaskQueue());
   LOG("Skipping failed, skipped %u frames", aFailure.mSkipped);
   mSkipRequest.Complete();
@@ -1597,17 +1583,17 @@ MediaFormatReader::OnVideoSkipFailed(Med
   switch (aFailure.mFailure) {
     case DemuxerFailureReason::END_OF_STREAM: MOZ_FALLTHROUGH;
     case DemuxerFailureReason::WAITING_FOR_DATA:
       // Some frames may have been output by the decoder since we initiated the
       // videoskip process and we know they would be late.
       DropDecodedSamples(TrackInfo::kVideoTrack);
       // We can't complete the skip operation, will just service a video frame
       // normally.
-      NotifyDecodingRequested(TrackInfo::kVideoTrack);
+      ScheduleUpdate(TrackInfo::kVideoTrack);
       break;
     case DemuxerFailureReason::CANCELED: MOZ_FALLTHROUGH;
     case DemuxerFailureReason::SHUTDOWN:
       if (mVideo.HasPromise()) {
         mVideo.RejectPromise(CANCELED, __func__);
       }
       break;
     default:
@@ -2015,22 +2001,21 @@ MediaFormatReader::GetMozDebugReaderData
     MonitorAutoLock mon(mVideo.mMonitor);
     videoName = mVideo.mDescription;
   }
 
   result += nsPrintfCString("audio decoder: %s\n", audioName);
   result += nsPrintfCString("audio frames decoded: %lld\n",
                             mAudio.mNumSamplesOutputTotal);
   if (HasAudio()) {
-    result += nsPrintfCString("audio state: ni=%d no=%d ie=%d demuxr:%d demuxq:%d decoder:%d tt:%f tths:%d in:%llu out:%llu qs=%u pending:%u waiting:%d sid:%u\n",
+    result += nsPrintfCString("audio state: ni=%d no=%d ie=%d demuxr:%d demuxq:%d tt:%f tths:%d in:%llu out:%llu qs=%u pending:%u waiting:%d sid:%u\n",
                               NeedInput(mAudio), mAudio.HasPromise(),
-                              mAudio.mInputExhausted,
+                              mAudio.mDecodePending,
                               mAudio.mDemuxRequest.Exists(),
                               int(mAudio.mQueuedSamples.Length()),
-                              mAudio.mDecodingRequested,
                               mAudio.mTimeThreshold
                               ? mAudio.mTimeThreshold.ref().Time().ToSeconds()
                               : -1.0,
                               mAudio.mTimeThreshold
                               ? mAudio.mTimeThreshold.ref().mHasSeeked
                               : -1,
                               mAudio.mNumSamplesInput, mAudio.mNumSamplesOutput,
                               unsigned(size_t(mAudio.mSizeOfQueue)),
@@ -2039,22 +2024,21 @@ MediaFormatReader::GetMozDebugReaderData
   }
   result += nsPrintfCString("video decoder: %s\n", videoName);
   result += nsPrintfCString("hardware video decoding: %s\n",
                             VideoIsHardwareAccelerated() ? "enabled" : "disabled");
   result += nsPrintfCString("video frames decoded: %lld (skipped:%lld)\n",
                             mVideo.mNumSamplesOutputTotal,
                             mVideo.mNumSamplesSkippedTotal);
   if (HasVideo()) {
-    result += nsPrintfCString("video state: ni=%d no=%d ie=%d demuxr:%d demuxq:%d decoder:%d tt:%f tths:%d in:%llu out:%llu qs=%u pending:%u waiting:%d sid:%u\n",
+    result += nsPrintfCString("video state: ni=%d no=%d ie=%d demuxr:%d demuxq:%d tt:%f tths:%d in:%llu out:%llu qs=%u pending:%u waiting:%d sid:%u\n",
                               NeedInput(mVideo), mVideo.HasPromise(),
-                              mVideo.mInputExhausted,
+                              mVideo.mDecodePending,
                               mVideo.mDemuxRequest.Exists(),
                               int(mVideo.mQueuedSamples.Length()),
-                              mVideo.mDecodingRequested,
                               mVideo.mTimeThreshold
                               ? mVideo.mTimeThreshold.ref().Time().ToSeconds()
                               : -1.0,
                               mVideo.mTimeThreshold
                               ? mVideo.mTimeThreshold.ref().mHasSeeked
                               : -1,
                               mVideo.mNumSamplesInput, mVideo.mNumSamplesOutput,
                               unsigned(size_t(mVideo.mSizeOfQueue)),
@@ -2082,14 +2066,14 @@ MediaFormatReader::SetBlankDecode(TrackT
 
   if (decoder.mIsBlankDecode == aIsBlankDecode) {
     return;
   }
 
   decoder.mIsBlankDecode = aIsBlankDecode;
   decoder.Flush();
   decoder.ShutdownDecoder();
-  NotifyDecodingRequested(TrackInfo::kVideoTrack); // Calls ScheduleUpdate().
+  ScheduleUpdate(TrackInfo::kVideoTrack);
 
   return;
 }
 
 } // namespace mozilla

--- a/dom/media/MediaFormatReader.h
+++ b/dom/media/MediaFormatReader.h
@@ -164,17 +164,16 @@ private:
   // Drain the current decoder.
   void DrainDecoder(TrackType aTrack);
   void NotifyNewOutput(TrackType aTrack, MediaData* aSample);
   void NotifyInputExhausted(TrackType aTrack);
   void NotifyDrainComplete(TrackType aTrack);
   void NotifyError(TrackType aTrack, MediaDataDecoderError aError = MediaDataDecoderError::FATAL_ERROR);
   void NotifyWaitingForData(TrackType aTrack);
   void NotifyEndOfStream(TrackType aTrack);
-  void NotifyDecodingRequested(TrackType aTrack);
 
   void ExtractCryptoInitData(nsTArray<uint8_t>& aInitData);
 
   // Initializes mLayersBackendType if possible.
   void InitLayersBackendType();
 
   // DecoderCallback proxies the MediaDataDecoderCallback calls to these
   // functions.
@@ -226,32 +225,29 @@ private:
   private:
     MediaFormatReader* mReader;
     TrackType mType;
   };
 
   struct DecoderData {
     DecoderData(MediaFormatReader* aOwner,
                 MediaData::Type aType,
-                uint32_t aDecodeAhead,
                 uint32_t aNumOfMaxError)
       : mOwner(aOwner)
       , mType(aType)
       , mMonitor("DecoderData")
       , mDescription("shutdown")
-      , mDecodeAhead(aDecodeAhead)
       , mUpdateScheduled(false)
       , mDemuxEOS(false)
       , mWaitingForData(false)
       , mReceivedNewData(false)
       , mDiscontinuity(true)
       , mDecoderInitialized(false)
-      , mDecodingRequested(false)
       , mOutputRequested(false)
-      , mInputExhausted(false)
+      , mDecodePending(false)
       , mNeedDraining(false)
       , mDraining(false)
       , mDrainComplete(false)
       , mNumOfConsecutiveError(0)
       , mMaxConsecutiveError(aNumOfMaxError)
       , mNumSamplesInput(0)
       , mNumSamplesOutput(0)
       , mNumSamplesOutputTotal(0)
@@ -284,17 +280,16 @@ private:
       if (mDecoder) {
         mDecoder->Shutdown();
       }
       mDescription = "shutdown";
       mDecoder = nullptr;
     }
 
     // Only accessed from reader's task queue.
-    uint32_t mDecodeAhead;
     bool mUpdateScheduled;
     bool mDemuxEOS;
     bool mWaitingForData;
     bool mReceivedNewData;
     bool mDiscontinuity;
 
     // Pending seek.
     MozPromiseRequestHolder<MediaTrackDemuxer::SeekPromise> mSeekRequest;
@@ -309,21 +304,24 @@ private:
       return !mWaitingPromise.IsEmpty();
     }
 
     // MediaDataDecoder handler's variables.
     // Decoder initialization promise holder.
     MozPromiseRequestHolder<MediaDataDecoder::InitPromise> mInitPromise;
     // False when decoder is created. True when decoder Init() promise is resolved.
     bool mDecoderInitialized;
-    // Set when decoding can proceed. It is reset when a decoding promise is
-    // rejected or prior a seek operation.
-    bool mDecodingRequested;
     bool mOutputRequested;
-    bool mInputExhausted;
+    // Set to true once the MediaDataDecoder has been fed a compressed sample.
+    // No more sample will be passed to the decoder while true.
+    // mDecodePending is reset when:
+    // 1- The decoder returns a sample
+    // 2- The decoder calls InputExhausted
+    // 3- The decoder is Flushed or Reset.
+    bool mDecodePending;
     bool mNeedDraining;
     bool mDraining;
     bool mDrainComplete;
 
     bool HasPendingDrain() const
     {
       return mDraining || mDrainComplete;
     }
@@ -373,19 +371,18 @@ private:
     // Flush the decoder if present and reset decoding related data.
     // Decoding will be suspended until mInputRequested is set again.
     // Following a flush, the decoder is ready to accept any new data.
     void Flush()
     {
       if (mDecoder) {
         mDecoder->Flush();
       }
-      mDecodingRequested = false;
       mOutputRequested = false;
-      mInputExhausted = false;
+      mDecodePending = false;
       mOutput.Clear();
       mNumSamplesInput = 0;
       mNumSamplesOutput = 0;
       mSizeOfQueue = 0;
       mDraining = false;
       mDrainComplete = false;
     }
 
@@ -395,20 +392,19 @@ private:
     // The track demuxer is *not* reset.
     void ResetState()
     {
       MOZ_ASSERT(mOwner->OnTaskQueue());
       mDemuxEOS = false;
       mWaitingForData = false;
       mDiscontinuity = true;
       mQueuedSamples.Clear();
-      mDecodingRequested = false;
       mOutputRequested = false;
-      mInputExhausted = false;
       mNeedDraining = false;
+      mDecodePending = false;
       mDraining = false;
       mDrainComplete = false;
       mTimeThreshold.reset();
       mLastSampleTime.reset();
       mOutput.Clear();
       mNumSamplesInput = 0;
       mNumSamplesOutput = 0;
       mSizeOfQueue = 0;
@@ -439,19 +435,18 @@ private:
     bool mIsBlankDecode;
 
   };
 
   class DecoderDataWithPromise : public DecoderData {
   public:
     DecoderDataWithPromise(MediaFormatReader* aOwner,
                            MediaData::Type aType,
-                           uint32_t aDecodeAhead,
                            uint32_t aNumOfMaxError)
-      : DecoderData(aOwner, aType, aDecodeAhead, aNumOfMaxError)
+      : DecoderData(aOwner, aType, aNumOfMaxError)
       , mHasPromise(false)
 
     {}
 
     bool HasPromise() const override
     {
       return mHasPromise;
     }
@@ -470,17 +465,16 @@ private:
       mHasPromise = false;
     }
 
     void RejectPromise(MediaDecoderReader::NotDecodedReason aReason,
                        const char* aMethodName) override
     {
       MOZ_ASSERT(mOwner->OnTaskQueue());
       mPromise.Reject(aReason, aMethodName);
-      mDecodingRequested = false;
       mHasPromise = false;
     }
 
   private:
     MozPromiseHolder<MediaDataPromise> mPromise;
     Atomic<bool> mHasPromise;
   };