diff --git a/dom/media/webm/NesteggPacketHolder.h b/dom/media/webm/NesteggPacketHolder.h
index 00a7b12cfb..0f8f9b63ab 100644
--- a/dom/media/webm/NesteggPacketHolder.h
+++ b/dom/media/webm/NesteggPacketHolder.h
@@ -22,10 +22,11 @@ public:
     : mPacket(nullptr)
     , mOffset(-1)
     , mTimestamp(-1)
+    , mDefaultDuration(-1)
     , mDuration(-1)
     , mIsKeyframe(false) {}
 
-  bool Init(nestegg_packet* aPacket, int64_t aOffset, unsigned aTrack, bool aIsKeyframe)
+  bool Init(nestegg_packet* aPacket, nestegg* aContext, int64_t aOffset, unsigned aTrack, bool aIsKeyframe)
   {
     uint64_t timestamp_ns;
     if (nestegg_packet_tstamp(aPacket, &timestamp_ns) == -1) {
@@ -44,6 +45,9 @@ public:
     if (!nestegg_packet_duration(aPacket, &duration_ns)) {
       mDuration = duration_ns / 1000;
     }
+    if (!nestegg_track_default_duration(aContext, mTrack, &duration_ns)) {
+      mDefaultDuration = duration_ns / 1000;
+    }
     return true;
   }
 
@@ -51,6 +55,7 @@ public:
   int64_t Offset() { MOZ_ASSERT(IsInitialized()); return mOffset; }
   int64_t Timestamp() { MOZ_ASSERT(IsInitialized()); return mTimestamp; }
   int64_t Duration() { MOZ_ASSERT(IsInitialized()); return mDuration; }
+  int64_t DefaultDuration() const { MOZ_ASSERT(IsInitialized()); return mDefaultDuration; }
   unsigned Track() { MOZ_ASSERT(IsInitialized()); return mTrack; }
   bool IsKeyframe() { MOZ_ASSERT(IsInitialized()); return mIsKeyframe; }
 
@@ -60,7 +65,7 @@ private:
     nestegg_free_packet(mPacket);
   }
 
-  bool IsInitialized() { return mOffset >= 0; }
+  bool IsInitialized() const { return mOffset >= 0; }
 
   nestegg_packet* mPacket;
 
@@ -72,8 +77,13 @@ private:
   int64_t mTimestamp;
 
   // Packet duration in microseconds; -1 if unknown or retrieval failed.
+  // https://www.webmproject.org/docs/container/#BlockDuration
   int64_t mDuration;
 
+  // Default duration in microseconds; -1 if unknown or retrieval failed.
+  // https://www.webmproject.org/docs/container/#Duration
+  int64_t mDefaultDuration;
+
   // Track ID.
   unsigned mTrack;
 
diff --git a/dom/media/webm/WebMDemuxer.cpp b/dom/media/webm/WebMDemuxer.cpp
index df28ee84e9..fc98db4d77 100644
--- a/dom/media/webm/WebMDemuxer.cpp
+++ b/dom/media/webm/WebMDemuxer.cpp
@@ -602,9 +602,10 @@ WebMDemuxer::GetNextPacket(TrackInfo::TrackType aType, MediaRawDataQueue *aSampl
   }
   int64_t tstamp = holder->Timestamp();
   int64_t duration = holder->Duration();
+  int64_t defaultDuration = holder->DefaultDuration();
   if (aType == TrackInfo::TrackType::kVideoTrack) {
-    WEBM_DEBUG("GetNextPacket(video): tstamp=%" PRId64 ", duration=%" PRId64,
-               tstamp, duration);
+    WEBM_DEBUG("GetNextPacket(video): tstamp=%" PRId64 ", duration=%" PRId64, ", defaultDuration=%" PRId64,
+               tstamp, duration, defaultDuration);
   }
 
   // The end time of this frame is the start time of the next frame. Fetch
@@ -646,6 +647,8 @@ WebMDemuxer::GetNextPacket(TrackInfo::TrackType aType, MediaRawDataQueue *aSampl
                (mIsMediaSource && mLastVideoFrameTime.isSome())) {
       next_tstamp = tstamp;
       next_tstamp += tstamp - mLastVideoFrameTime.refOr(0);
+    } else if (defaultDuration >= 0) {
+      next_tstamp = tstamp + defaultDuration;
     } else if (mVideoFrameEndTimeBeforeReset) {
       WEBM_DEBUG("Setting next timestamp to be %" PRId64 " us",
                  mVideoFrameEndTimeBeforeReset.value());
@@ -883,7 +886,7 @@ WebMDemuxer::DemuxPacket(TrackInfo::TrackType aType,
 
   int64_t offset = Resource(aType).Tell();
   RefPtr<NesteggPacketHolder> holder = new NesteggPacketHolder();
-  if (!holder->Init(packet, offset, track, false)) {
+  if (!holder->Init(packet, Context(aType), offset, track, false)) {
     return NS_ERROR_DOM_MEDIA_DEMUXER_ERR;
   }
 
diff --git a/layout/media/symbols.def.in b/layout/media/symbols.def.in
index 6ebb26c722..7f8af25886 100644
--- a/layout/media/symbols.def.in
+++ b/layout/media/symbols.def.in
@@ -27,6 +27,7 @@ nestegg_track_codec_data_count
 nestegg_track_codec_id
 nestegg_track_content_enc_key_id
 nestegg_track_count
+nestegg_track_default_duration
 nestegg_get_cue_point
 nestegg_track_seek
 nestegg_track_type