diff --git a/dom/media/platforms/ffmpeg/FFmpegVideoDecoder.h b/dom/media/platforms/ffmpeg/FFmpegVideoDecoder.h
--- a/dom/media/platforms/ffmpeg/FFmpegVideoDecoder.h
+++ b/dom/media/platforms/ffmpeg/FFmpegVideoDecoder.h
@@ -106,10 +106,11 @@
   bool IsHardwareAccelerated(nsACString& aFailureReason) const override;
   bool IsHardwareAccelerated() const {
     nsAutoCString dummy;
     return IsHardwareAccelerated(dummy);
   }
+  void UpdateDecodeTimes(TimeStamp aDecodeStart);
 
 #if LIBAVCODEC_VERSION_MAJOR >= 57 && LIBAVUTIL_VERSION_MAJOR >= 56
   layers::TextureClient* AllocateTextureClientForImage(
       struct AVCodecContext* aCodecContext, layers::PlanarYCbCrImage* aImage);
 
@@ -142,10 +143,15 @@
   static nsTArray<AVCodecID> mAcceleratedFormats;
 #endif
   RefPtr<KnowsCompositor> mImageAllocator;
   RefPtr<ImageContainer> mImageContainer;
   VideoInfo mInfo;
+  int mDecodedFrames;
+#if LIBAVCODEC_VERSION_MAJOR >= 58
+  int mDecodedFramesLate;
+#endif
+  float mAverangeDecodeTime;
 
   class PtsCorrectionContext {
    public:
     PtsCorrectionContext();
     int64_t GuessCorrectPts(int64_t aPts, int64_t aDts);
diff --git a/dom/media/platforms/ffmpeg/FFmpegVideoDecoder.cpp b/dom/media/platforms/ffmpeg/FFmpegVideoDecoder.cpp
--- a/dom/media/platforms/ffmpeg/FFmpegVideoDecoder.cpp
+++ b/dom/media/platforms/ffmpeg/FFmpegVideoDecoder.cpp
@@ -383,10 +383,15 @@
       mDisplay(nullptr),
 #endif
       mImageAllocator(aAllocator),
       mImageContainer(aImageContainer),
       mInfo(aConfig),
+      mDecodedFrames(0),
+#if LIBAVCODEC_VERSION_MAJOR >= 58
+      mDecodedFramesLate(0),
+#endif
+      mAverangeDecodeTime(0),
       mLowLatency(aLowLatency) {
   FFMPEG_LOG("FFmpegVideoDecoder::FFmpegVideoDecoder MIME %s Codec ID %d",
              aConfig.mMimeType.get(), mCodecID);
   // Use a new MediaByteBuffer as the object will be modified during
   // initialization.
@@ -769,17 +774,41 @@
 #else
   return aFrame->pkt_pts;
 #endif
 }
 
+void FFmpegVideoDecoder<LIBAV_VER>::UpdateDecodeTimes(TimeStamp aDecodeStart) {
+  mDecodedFrames++;
+  float decodeTime = (TimeStamp::Now() - aDecodeStart).ToMilliseconds();
+  mAverangeDecodeTime =
+      (mAverangeDecodeTime * (mDecodedFrames - 1) + decodeTime) /
+      mDecodedFrames;
+  FFMPEG_LOG("  averange frame decode time %.2f ms decoded frames %d\n",
+             mAverangeDecodeTime, mDecodedFrames);
+#if LIBAVCODEC_VERSION_MAJOR >= 58
+  int frameDuration = mFrame->pkt_duration;
+  if (frameDuration > 0 && frameDuration / 1000.0 < decodeTime) {
+    mDecodedFramesLate++;
+    FFMPEG_LOG(
+        "  slow decode: failed to decode in time, frame duration %.2f ms, "
+        "decode time %.2f\n",
+        frameDuration / 1000.0, decodeTime);
+    FFMPEG_LOG("  all decoded frames / late decoded frames %d/%d\n",
+               mDecodedFrames, mDecodedFramesLate);
+  }
+#endif
+}
+
 MediaResult FFmpegVideoDecoder<LIBAV_VER>::DoDecode(
     MediaRawData* aSample, uint8_t* aData, int aSize, bool* aGotFrame,
     MediaDataDecoder::DecodedData& aResults) {
   MOZ_ASSERT(mTaskQueue->IsOnCurrentThread());
   AVPacket packet;
   mLib->av_init_packet(&packet);
 
+  TimeStamp decodeStart = TimeStamp::Now();
+
   packet.data = aData;
   packet.size = aSize;
   packet.dts = aSample->mTimecode.ToMicroseconds();
   packet.pts = aSample->mTime.ToMicroseconds();
   packet.flags = aSample->mKeyframe ? AV_PKT_FLAG_KEY : 0;
@@ -794,11 +823,10 @@
     // at a time, and we immediately call avcodec_receive_frame right after.
     FFMPEG_LOG("avcodec_send_packet error: %d", res);
     return MediaResult(NS_ERROR_DOM_MEDIA_DECODE_ERR,
                        RESULT_DETAIL("avcodec_send_packet error: %d", res));
   }
-
   if (aGotFrame) {
     *aGotFrame = false;
   }
   do {
     if (!PrepareFrame()) {
@@ -831,10 +859,13 @@
       FFMPEG_LOG("  avcodec_receive_frame error: %d", res);
       return MediaResult(NS_ERROR_DOM_MEDIA_DECODE_ERR,
                          RESULT_DETAIL("avcodec_receive_frame error: %d", res));
     }
 
+    UpdateDecodeTimes(decodeStart);
+    decodeStart = TimeStamp::Now();
+
     MediaResult rv;
 #  ifdef MOZ_WAYLAND_USE_VAAPI
     if (IsHardwareAccelerated()) {
       rv = CreateImageVAAPI(mFrame->pkt_pos, GetFramePts(mFrame),
                             mFrame->pkt_duration, aResults);
@@ -898,10 +929,12 @@
       *aGotFrame = false;
     }
     return NS_OK;
   }
 
+  UpdateDecodeTimes(decodeStart);
+
   // If we've decoded a frame then we need to output it
   int64_t pts =
       mPtsContext.GuessCorrectPts(GetFramePts(mFrame), mFrame->pkt_dts);
   // Retrieve duration from dts.
   // We use the first entry found matching this dts (this is done to