diff --git a/dom/media/AudioStreamTrack.h b/dom/media/AudioStreamTrack.h
index 278e14fc48ce..aa1e2fd8854b 100644
--- a/dom/media/AudioStreamTrack.h
+++ b/dom/media/AudioStreamTrack.h
@@ -27,6 +27,17 @@ public:
 
   // WebIDL
   void GetKind(nsAString& aKind) override { aKind.AssignLiteral("audio"); }
+
+protected:
+  already_AddRefed<MediaStreamTrack> CloneInternal(DOMMediaStream* aOwningStream,
+                                                   TrackID aTrackID) override
+  {
+    return do_AddRef(new AudioStreamTrack(aOwningStream,
+                                          aTrackID,
+                                          mInputTrackID,
+                                          mLabel,
+                                          mSource));
+  }
 };
 
 } // namespace dom
diff --git a/dom/media/DOMMediaStream.cpp b/dom/media/DOMMediaStream.cpp
index 4ddcca79e63d..09b22f7e8fb6 100644
--- a/dom/media/DOMMediaStream.cpp
+++ b/dom/media/DOMMediaStream.cpp
@@ -863,18 +863,51 @@ DOMMediaStream::CreateOwnDOMTrack(TrackID aTrackID, MediaSegment::Type aType,
 
   LOG(LogLevel::Debug, ("DOMMediaStream %p Created new track %p with ID %u", this, track, aTrackID));
 
-  RefPtr<TrackPort> ownedTrackPort =
-    new TrackPort(mOwnedPort, track, TrackPort::InputPortOwnership::EXTERNAL);
-  mOwnedTracks.AppendElement(ownedTrackPort.forget());
+  mOwnedTracks.AppendElement(
+    new TrackPort(mOwnedPort, track, TrackPort::InputPortOwnership::EXTERNAL));
 
-  RefPtr<TrackPort> playbackTrackPort =
-    new TrackPort(mPlaybackPort, track, TrackPort::InputPortOwnership::EXTERNAL);
-  mTracks.AppendElement(playbackTrackPort.forget());
+  mTracks.AppendElement(
+    new TrackPort(mPlaybackPort, track, TrackPort::InputPortOwnership::EXTERNAL));
 
   NotifyTrackAdded(track);
   return track;
 }
 
+already_AddRefed<MediaStreamTrack>
+DOMMediaStream::CreateClonedDOMTrack(MediaStreamTrack& aTrack,
+                                     TrackID aCloneTrackID)
+{
+  MOZ_RELEASE_ASSERT(mOwnedStream);
+  MOZ_RELEASE_ASSERT(mPlaybackStream);
+  MOZ_RELEASE_ASSERT(IsTrackIDExplicit(aCloneTrackID));
+
+  TrackID inputTrackID = aTrack.mInputTrackID;
+  MediaStream* inputStream = aTrack.GetInputStream();
+
+  RefPtr<MediaStreamTrack> newTrack = aTrack.CloneInternal(this, aCloneTrackID);
+
+  newTrack->mOriginalTrack =
+    aTrack.mOriginalTrack ? aTrack.mOriginalTrack.get() : &aTrack;
+
+  LOG(LogLevel::Debug, ("DOMMediaStream %p Created new track %p cloned from stream %p track %d",
+                        this, newTrack.get(), inputStream, inputTrackID));
+
+  RefPtr<MediaInputPort> inputPort =
+    mOwnedStream->AllocateInputPort(inputStream, inputTrackID, aCloneTrackID);
+
+  mOwnedTracks.AppendElement(
+    new TrackPort(inputPort, newTrack, TrackPort::InputPortOwnership::OWNED));
+
+  mTracks.AppendElement(
+    new TrackPort(mPlaybackPort, newTrack, TrackPort::InputPortOwnership::EXTERNAL));
+
+  NotifyTrackAdded(newTrack);
+
+  newTrack->SetEnabled(aTrack.Enabled());
+
+  return newTrack.forget();
+}
+
 MediaStreamTrack*
 DOMMediaStream::FindOwnedDOMTrack(MediaStream* aInputStream,
                                   TrackID aInputTrackID) const
@@ -907,7 +940,11 @@ DOMMediaStream::FindOwnedTrackPort(const MediaStreamTrack& aTrack) const
 MediaStreamTrack*
 DOMMediaStream::FindPlaybackDOMTrack(MediaStream* aInputStream, TrackID aInputTrackID) const
 {
-  MOZ_RELEASE_ASSERT(mPlaybackStream);
+  if (!mPlaybackStream) {
+    // One would think we can assert mPlaybackStream here, but track clones have
+    // a dummy DOMMediaStream that doesn't have a playback stream, so we can't.
+    return nullptr;
+  }
 
   for (const RefPtr<TrackPort>& info : mTracks) {
     if (info->GetInputPort() == mPlaybackPort &&
diff --git a/dom/media/DOMMediaStream.h b/dom/media/DOMMediaStream.h
index 83a490b7215b..bd0179b0a31a 100644
--- a/dom/media/DOMMediaStream.h
+++ b/dom/media/DOMMediaStream.h
@@ -518,6 +518,14 @@ public:
                                       const nsString& aLabel,
                                       MediaStreamTrackSource* aSource);
 
+  /**
+   * Creates a MediaStreamTrack cloned from aTrack, adds it to mTracks and
+   * returns it.
+   * aCloneTrackID is the TrackID the new track will get in mOwnedStream.
+   */
+  already_AddRefed<MediaStreamTrack> CreateClonedDOMTrack(MediaStreamTrack& aTrack,
+                                                          TrackID aCloneTrackID);
+
   // When the initial set of tracks has been added, run
   // aCallback->NotifyTracksAvailable.
   // It is allowed to do anything, including run script.
diff --git a/dom/media/MediaStreamTrack.cpp b/dom/media/MediaStreamTrack.cpp
index ce62525c9c04..2060bc6aa13c 100644
--- a/dom/media/MediaStreamTrack.cpp
+++ b/dom/media/MediaStreamTrack.cpp
@@ -200,6 +200,22 @@ MediaStreamTrack::RemovePrincipalChangeObserver(
   return mPrincipalChangeObservers.RemoveElement(aObserver);
 }
 
+already_AddRefed<MediaStreamTrack>
+MediaStreamTrack::Clone()
+{
+  // MediaStreamTracks are currently governed by streams, so we need a dummy
+  // DOMMediaStream to own our track clone. The dummy will never see any
+  // dynamically created tracks (no input stream) so no need for a SourceGetter.
+  RefPtr<DOMMediaStream> newStream =
+    new DOMMediaStream(mOwningStream->GetParentObject(), nullptr);
+
+  MediaStreamGraph* graph = Graph();
+  newStream->InitOwnedStreamCommon(graph);
+  newStream->InitPlaybackStreamCommon(graph);
+
+  return newStream->CreateClonedDOMTrack(*this, mTrackID);
+}
+
 DOMMediaStream*
 MediaStreamTrack::GetInputDOMStream()
 {
diff --git a/dom/media/MediaStreamTrack.h b/dom/media/MediaStreamTrack.h
index 3bfdd47c59b4..ab4491a4407c 100644
--- a/dom/media/MediaStreamTrack.h
+++ b/dom/media/MediaStreamTrack.h
@@ -215,6 +215,7 @@ public:
   void Stop();
   already_AddRefed<Promise>
   ApplyConstraints(const dom::MediaTrackConstraints& aConstraints, ErrorResult &aRv);
+  already_AddRefed<MediaStreamTrack> Clone();
 
   bool Ended() const { return mEnded; }
   // Notifications from the MediaStreamGraph
@@ -282,6 +283,14 @@ protected:
   // the original track's owning DOMMediaStream is returned.
   DOMMediaStream* GetInputDOMStream();
 
+  /**
+   * Creates a new MediaStreamTrack with the same type, input track ID and
+   * source as this MediaStreamTrack.
+   * aTrackID is the TrackID the new track will have in its owned stream.
+   */
+  virtual already_AddRefed<MediaStreamTrack> CloneInternal(DOMMediaStream* aOwningStream,
+                                                           TrackID aTrackID) = 0;
+
   nsTArray<PrincipalChangeObserver<MediaStreamTrack>*> mPrincipalChangeObservers;
 
   RefPtr<DOMMediaStream> mOwningStream;
diff --git a/dom/media/VideoStreamTrack.h b/dom/media/VideoStreamTrack.h
index cd40e6fb21eb..1f2b9e793403 100644
--- a/dom/media/VideoStreamTrack.h
+++ b/dom/media/VideoStreamTrack.h
@@ -27,6 +27,17 @@ public:
 
   // WebIDL
   void GetKind(nsAString& aKind) override { aKind.AssignLiteral("video"); }
+
+protected:
+  already_AddRefed<MediaStreamTrack> CloneInternal(DOMMediaStream* aOwningStream,
+                                                   TrackID aTrackID) override
+  {
+    return do_AddRef(new VideoStreamTrack(aOwningStream,
+                                          aTrackID,
+                                          mInputTrackID,
+                                          mLabel,
+                                          mSource));
+  }
 };
 
 } // namespace dom
diff --git a/dom/webidl/MediaStreamTrack.webidl b/dom/webidl/MediaStreamTrack.webidl
index bea52288703b..71a335029441 100644
--- a/dom/webidl/MediaStreamTrack.webidl
+++ b/dom/webidl/MediaStreamTrack.webidl
@@ -76,7 +76,7 @@ interface MediaStreamTrack : EventTarget {
 //  readonly    attribute boolean               remote;
 //  readonly    attribute MediaStreamTrackState readyState;
 //                attribute EventHandler          onended;
-//  MediaStreamTrack       clone ();
+    MediaStreamTrack       clone ();
     void                   stop ();
 //  MediaTrackCapabilities getCapabilities ();
 //  MediaTrackConstraints  getConstraints ();