--- a/dom/camera/DOMCameraControl.cpp
+++ b/dom/camera/DOMCameraControl.cpp
@@ -524,17 +524,17 @@ nsDOMCameraControl::GetCameraStream() co
   return mInput;
 }
 
 void
 nsDOMCameraControl::TrackCreated(TrackID aTrackID) {
   // This track is not connected through a port.
   MediaInputPort* inputPort = nullptr;
   dom::VideoStreamTrack* track =
-    new dom::VideoStreamTrack(this, aTrackID,
+    new dom::VideoStreamTrack(this, aTrackID, aTrackID,
                               new BasicUnstoppableTrackSource());
   RefPtr<TrackPort> port =
     new TrackPort(inputPort, track,
                   TrackPort::InputPortOwnership::OWNED);
   mTracks.AppendElement(port.forget());
   NotifyTrackAdded(track);
 }
 

--- a/dom/media/AudioStreamTrack.h
+++ b/dom/media/AudioStreamTrack.h
@@ -10,18 +10,19 @@
 #include "DOMMediaStream.h"
 
 namespace mozilla {
 namespace dom {
 
 class AudioStreamTrack : public MediaStreamTrack {
 public:
   AudioStreamTrack(DOMMediaStream* aStream, TrackID aTrackID,
+                   TrackID aInputTrackID,
                    MediaStreamTrackSource* aSource)
-    : MediaStreamTrack(aStream, aTrackID, aSource) {}
+    : MediaStreamTrack(aStream, aTrackID, aInputTrackID, aSource) {}
 
   virtual JSObject* WrapObject(JSContext* aCx, JS::Handle<JSObject*> aGivenProto) override;
 
   virtual AudioStreamTrack* AsAudioStreamTrack() override { return this; }
 
   // WebIDL
   virtual void GetKind(nsAString& aKind) override { aKind.AssignLiteral("audio"); }
 };

--- a/dom/media/DOMMediaStream.cpp
+++ b/dom/media/DOMMediaStream.cpp
@@ -785,20 +785,20 @@ DOMMediaStream::CreateOwnDOMTrack(TrackI
   MOZ_RELEASE_ASSERT(mInputStream);
   MOZ_RELEASE_ASSERT(mOwnedStream);
 
   MOZ_ASSERT(FindOwnedDOMTrack(GetOwnedStream(), aTrackID) == nullptr);
 
   MediaStreamTrack* track;
   switch (aType) {
   case MediaSegment::AUDIO:
-    track = new AudioStreamTrack(this, aTrackID, aSource);
+    track = new AudioStreamTrack(this, aTrackID, aTrackID, aSource);
     break;
   case MediaSegment::VIDEO:
-    track = new VideoStreamTrack(this, aTrackID, aSource);
+    track = new VideoStreamTrack(this, aTrackID, aTrackID, aSource);
     break;
   default:
     MOZ_CRASH("Unhandled track type");
   }
 
   LOG(LogLevel::Debug, ("DOMMediaStream %p Created new track %p with ID %u", this, track, aTrackID));
 
   RefPtr<TrackPort> ownedTrackPort =
@@ -833,17 +833,17 @@ DOMMediaStream::FindOwnedDOMTrack(MediaS
 MediaStreamTrack*
 DOMMediaStream::FindPlaybackDOMTrack(MediaStream* aInputStream, TrackID aInputTrackID) const
 {
   MOZ_RELEASE_ASSERT(mPlaybackStream);
 
   for (const RefPtr<TrackPort>& info : mTracks) {
     if (info->GetInputPort() == mPlaybackPort &&
         aInputStream == mOwnedStream &&
-        aInputTrackID == info->GetTrack()->GetTrackID()) {
+        info->GetTrack()->GetInputTrackID() == aInputTrackID) {
       // This track is in our owned and playback streams.
       return info->GetTrack();
     }
     if (info->GetInputPort() &&
         info->GetInputPort()->GetSource() == aInputStream &&
         info->GetSourceTrackId() == aInputTrackID) {
       // This track is owned externally but in our playback stream.
       MOZ_ASSERT(aInputTrackID != TRACK_NONE);

--- a/dom/media/MediaStreamTrack.cpp
+++ b/dom/media/MediaStreamTrack.cpp
@@ -15,18 +15,20 @@
 
 static PRLogModuleInfo* gMediaStreamTrackLog;
 #define LOG(type, msg) MOZ_LOG(gMediaStreamTrackLog, type, msg)
 
 namespace mozilla {
 namespace dom {
 
 MediaStreamTrack::MediaStreamTrack(DOMMediaStream* aStream, TrackID aTrackID,
+                                   TrackID aInputTrackID,
                                    MediaStreamTrackSource* aSource)
-  : mOwningStream(aStream), mTrackID(aTrackID), mSource(aSource),
+  : mOwningStream(aStream), mTrackID(aTrackID),
+    mInputTrackID(aInputTrackID), mSource(aSource),
     mEnded(false), mEnabled(true), mRemote(aSource->IsRemote()), mStopped(false)
 {
 
   if (!gMediaStreamTrackLog) {
     gMediaStreamTrackLog = PR_NewLogModule("MediaStreamTrack");
   }
 
   MOZ_RELEASE_ASSERT(mSource);

--- a/dom/media/MediaStreamTrack.h
+++ b/dom/media/MediaStreamTrack.h
@@ -130,16 +130,17 @@ protected:
  */
 class MediaStreamTrack : public DOMEventTargetHelper {
 public:
   /**
    * aTrackID is the MediaStreamGraph track ID for the track in the
    * MediaStream owned by aStream.
    */
   MediaStreamTrack(DOMMediaStream* aStream, TrackID aTrackID,
+                   TrackID aInputTrackID,
                    MediaStreamTrackSource* aSource);
 
   NS_DECL_ISUPPORTS_INHERITED
   NS_DECL_CYCLE_COLLECTION_CLASS_INHERITED(MediaStreamTrack,
                                            DOMEventTargetHelper)
 
   DOMMediaStream* GetParentObject() const { return mOwningStream; }
   virtual JSObject* WrapObject(JSContext* aCx, JS::Handle<JSObject*> aGivenProto) override = 0;
@@ -149,16 +150,22 @@ public:
    */
   DOMMediaStream* GetStream() const { return mOwningStream; }
 
   /**
    * Returns the TrackID this stream has in its owning DOMMediaStream's Owned
    * stream.
    */
   TrackID GetTrackID() const { return mTrackID; }
+
+  /**
+   * Returns the TrackID this MediaStreamTrack has in its input MSG-MediaStream.
+   */
+  TrackID GetInputTrackID() const { return mInputTrackID; }
+
   virtual AudioStreamTrack* AsAudioStreamTrack() { return nullptr; }
   virtual VideoStreamTrack* AsVideoStreamTrack() { return nullptr; }
 
   // WebIDL
   virtual void GetKind(nsAString& aKind) = 0;
   void GetId(nsAString& aID) const;
   void GetLabel(nsAString& aLabel) { aLabel.Truncate(); }
   bool Enabled() { return mEnabled; }
@@ -181,16 +188,17 @@ public:
   // need to surface this to content.
   void AssignId(const nsAString& aID) { mID = aID; }
 
 protected:
   virtual ~MediaStreamTrack();
 
   RefPtr<DOMMediaStream> mOwningStream;
   TrackID mTrackID;
+  TrackID mInputTrackID;
   const RefPtr<MediaStreamTrackSource> mSource;
   RefPtr<MediaStreamTrack> mOriginalTrack;
   nsString mID;
   bool mEnded;
   bool mEnabled;
   const bool mRemote;
   bool mStopped;
 };

--- a/dom/media/VideoStreamTrack.h
+++ b/dom/media/VideoStreamTrack.h
@@ -10,18 +10,19 @@
 #include "DOMMediaStream.h"
 
 namespace mozilla {
 namespace dom {
 
 class VideoStreamTrack : public MediaStreamTrack {
 public:
   VideoStreamTrack(DOMMediaStream* aStream, TrackID aTrackID,
+                   TrackID aInputTrackID,
                    MediaStreamTrackSource* aSource)
-    : MediaStreamTrack(aStream, aTrackID, aSource) {}
+    : MediaStreamTrack(aStream, aTrackID, aInputTrackID, aSource) {}
 
   virtual JSObject* WrapObject(JSContext* aCx, JS::Handle<JSObject*> aGivenProto) override;
 
   virtual VideoStreamTrack* AsVideoStreamTrack() override { return this; }
 
   // WebIDL
   virtual void GetKind(nsAString& aKind) override { aKind.AssignLiteral("video"); }
 };