diff --git a/dom/media/webm/WebMDemuxer.cpp b/dom/media/webm/WebMDemuxer.cpp
index ae729ff541eb..375dd0466edd 100644
--- a/dom/media/webm/WebMDemuxer.cpp
+++ b/dom/media/webm/WebMDemuxer.cpp
@@ -355,6 +355,13 @@ WebMDemuxer::ReadMetadata()
         continue;
       }
 
+      uint64_t defaultDuration;
+      r = nestegg_track_default_duration(context, track, &defaultDuration);
+      if (r >= 0) {
+        mVideoDefaultDuration =
+          Some(uint64_t(media::TimeUnit::FromNanoseconds(defaultDuration).ToMicroseconds()));
+      }
+
       mVideoTrack = track;
       mHasVideo = true;
 
@@ -395,6 +402,13 @@ WebMDemuxer::ReadMetadata()
         return NS_ERROR_FAILURE;
       }
 
+      uint64_t defaultDuration;
+      r = nestegg_track_default_duration(context, track, &defaultDuration);
+      if (r >= 0) {
+        mAudioDefaultDuration =
+          Some(uint64_t(media::TimeUnit::FromNanoseconds(defaultDuration).ToMicroseconds()));
+      }
+
       mAudioTrack = track;
       mHasAudio = true;
       mAudioCodec = nestegg_track_codec_id(context, track);
@@ -587,7 +601,11 @@ WebMDemuxer::GetNextPacket(TrackInfo::TrackType aType, MediaRawDataQueue *aSampl
     } else if (!mIsMediaSource ||
                (mIsMediaSource && mLastAudioFrameTime.isSome())) {
       next_tstamp = tstamp;
-      next_tstamp += tstamp - mLastAudioFrameTime.refOr(0);
+      if (mAudioDefaultDuration.isSome()) {
+        next_tstamp += mAudioDefaultDuration.ref();
+      } else {
+        next_tstamp += tstamp - mLastAudioFrameTime.refOr(0);
+      }
     } else {
       PushAudioPacket(holder);
     }
@@ -602,7 +620,11 @@ WebMDemuxer::GetNextPacket(TrackInfo::TrackType aType, MediaRawDataQueue *aSampl
     } else if (!mIsMediaSource ||
                (mIsMediaSource && mLastVideoFrameTime.isSome())) {
       next_tstamp = tstamp;
-      next_tstamp += tstamp - mLastVideoFrameTime.refOr(0);
+      if (mVideoDefaultDuration.isSome()) {
+        next_tstamp += mVideoDefaultDuration.ref();
+      } else {
+        next_tstamp += tstamp - mLastVideoFrameTime.refOr(0);
+      }
     } else {
       PushVideoPacket(holder);
     }
diff --git a/dom/media/webm/WebMDemuxer.h b/dom/media/webm/WebMDemuxer.h
index 6fff38e7dc35..4fa89cbb8f8a 100644
--- a/dom/media/webm/WebMDemuxer.h
+++ b/dom/media/webm/WebMDemuxer.h
@@ -220,6 +220,8 @@ private:
   // previous frame's timestamp.  In NS.
   Maybe<int64_t> mLastAudioFrameTime;
   Maybe<int64_t> mLastVideoFrameTime;
+  Maybe<uint64_t> mAudioDefaultDuration;
+  Maybe<uint64_t> mVideoDefaultDuration;
 
   // Codec ID of audio track
   int mAudioCodec;