--- a/dom/media/MediaFormatReader.cpp
+++ b/dom/media/MediaFormatReader.cpp
@@ -1418,38 +1418,68 @@ MediaFormatReader::Reset(TrackType aTrac
 
   decoder.ResetState();
   decoder.Flush();
 
   LOG("Reset(%s) END", TrackTypeToStr(aTrack));
 }
 
 void
+MediaFormatReader::DropDecodedSamples(TrackType aTrack)
+{
+  MOZ_ASSERT(OnTaskQueue());
+  auto& decoder = GetDecoderData(aTrack);
+  size_t lengthDecodedQueue = decoder.mOutput.Length();
+  if (lengthDecodedQueue && decoder.mTimeThreshold.isSome()) {
+    TimeUnit time =
+      TimeUnit::FromMicroseconds(decoder.mOutput.LastElement()->mTime);
+    if (time >= decoder.mTimeThreshold.ref().Time()) {
+      // We would have reached our internal seek target.
+      decoder.mTimeThreshold.reset();
+    }
+  }
+  decoder.mOutput.Clear();
+  decoder.mSizeOfQueue -= lengthDecodedQueue;
+  if (aTrack == TrackInfo::kVideoTrack && mDecoder) {
+    mDecoder->NotifyDecodedFrames(0, 0, lengthDecodedQueue);
+  }
+}
+
+void
 MediaFormatReader::SkipVideoDemuxToNextKeyFrame(media::TimeUnit aTimeThreshold)
 {
   MOZ_ASSERT(OnTaskQueue());
   MOZ_ASSERT(mVideo.HasPromise());
   LOG("Skipping up to %lld", aTimeThreshold.ToMicroseconds());
 
+  // We've reached SkipVideoDemuxToNextKeyFrame when our decoding is late.
+  // As such we can drop all already decoded samples and discard all pending
+  // samples.
+  // TODO: Ideally we should set mOutputRequested to false so that all pending
+  // frames are dropped too. However, we can't do such thing as the code assumes
+  // that the decoder just got flushed. Once bug 1257107 land, we could set the
+  // decoder threshold to the value of currentTime.
+  DropDecodedSamples(TrackInfo::kVideoTrack);
+
   mSkipRequest.Begin(mVideo.mTrackDemuxer->SkipToNextRandomAccessPoint(aTimeThreshold)
                           ->Then(OwnerThread(), __func__, this,
                                  &MediaFormatReader::OnVideoSkipCompleted,
                                  &MediaFormatReader::OnVideoSkipFailed));
   return;
 }
 
 void
 MediaFormatReader::VideoSkipReset(uint32_t aSkipped)
 {
   MOZ_ASSERT(OnTaskQueue());
-  // I think it's still possible for an output to have been sent from the decoder
-  // and is currently sitting in our event queue waiting to be processed. The following
-  // flush won't clear it, and when we return to the event loop it'll be added to our
-  // output queue and be used.
-  // This code will count that as dropped, which was the intent, but not quite true.
+
+  // 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);
+  // Report the pending frames as dropped.
   if (mDecoder) {
     mDecoder->NotifyDecodedFrames(0, 0, SizeOfVideoQueueInFrames());
   }
 
   // Cancel any pending demux request and pending demuxed samples.
   mVideo.mDemuxRequest.DisconnectIfExists();
   Reset(TrackType::kVideoTrack);
 
@@ -1478,16 +1508,19 @@ MediaFormatReader::OnVideoSkipFailed(Med
   MOZ_ASSERT(OnTaskQueue());
   LOG("Skipping failed, skipped %u frames", aFailure.mSkipped);
   mSkipRequest.Complete();
 
   MOZ_ASSERT(mVideo.HasPromise());
   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);
       break;
     case DemuxerFailureReason::CANCELED: MOZ_FALLTHROUGH;
     case DemuxerFailureReason::SHUTDOWN:
       if (mVideo.HasPromise()) {
         mVideo.RejectPromise(CANCELED, __func__);

--- a/dom/media/MediaFormatReader.h
+++ b/dom/media/MediaFormatReader.h
@@ -174,16 +174,17 @@ private:
 
   // DecoderCallback proxies the MediaDataDecoderCallback calls to these
   // functions.
   void Output(TrackType aType, MediaData* aSample);
   void InputExhausted(TrackType aTrack);
   void Error(TrackType aTrack);
   void Reset(TrackType aTrack);
   void DrainComplete(TrackType aTrack);
+  void DropDecodedSamples(TrackType aTrack);
 
   bool ShouldSkip(bool aSkipToNextKeyframe, media::TimeUnit aTimeThreshold);
 
   size_t SizeOfQueue(TrackType aTrack);
 
   RefPtr<PDMFactory> mPlatform;
 
   class DecoderCallback : public MediaDataDecoderCallback {