--- a/dom/media/MediaStreamGraph.cpp
+++ b/dom/media/MediaStreamGraph.cpp
@@ -261,16 +261,28 @@ MediaStreamGraphImpl::ExtractPendingInpu
 
         data->mEndOfFlushedData += segment->GetDuration();
         aStream->mTracks.AddTrack(data->mID, data->mStart, segment);
         // The track has taken ownership of data->mData, so let's replace
         // data->mData with an empty clone.
         data->mData = segment->CreateEmptyClone();
         data->mCommands &= ~SourceMediaStream::TRACK_CREATE;
         shouldNotifyTrackCreated = true;
+
+        for (int32_t i = aStream->mPendingDirectTrackListeners.Length() - 1;
+               i >= 0; i--) {
+          if (aStream->mPendingDirectTrackListeners[i].mTrackID != data->mID) {
+            continue;
+          }
+
+          RefPtr<DirectMediaStreamTrackListener> l =
+            aStream->mPendingDirectTrackListeners[i].mListener;
+          aStream->mPendingDirectTrackListeners.RemoveElementAt(i);
+          aStream->AddDirectTrackListenerImpl(l.forget(), data->mID);
+        }
       } else if (data->mData->GetDuration() > 0) {
         MediaSegment* dest = aStream->mTracks.FindTrack(data->mID)->GetSegment();
         STREAM_LOG(LogLevel::Verbose, ("SourceMediaStream %p track %d, advancing end from %lld to %lld",
                                     aStream, data->mID,
                                     int64_t(dest->GetDuration()),
                                     int64_t(dest->GetDuration() + data->mData->GetDuration())));
         data->mEndOfFlushedData += data->mData->GetDuration();
         dest->AppendFrom(data->mData);
@@ -2923,20 +2935,23 @@ SourceMediaStream::AddDirectTrackListene
 
       TrackBound<DirectMediaStreamTrackListener>* sourceListener =
         mDirectTrackListeners.AppendElement();
       sourceListener->mListener = listener;
       sourceListener->mTrackID = aTrackID;
     }
   }
   if (!found) {
-    STREAM_LOG(LogLevel::Warning, ("Couldn't find source track for direct track listener %p",
-                                   listener.get()));
-    listener->NotifyDirectListenerInstalled(
-      DirectMediaStreamTrackListener::InstallationResult::TRACK_NOT_FOUND_AT_SOURCE);
+    STREAM_LOG(LogLevel::Info, ("Couldn't find source track for direct track "
+                                "listener %p. Waiting for the track to appear.",
+                                listener.get()));
+    TrackBound<DirectMediaStreamTrackListener>* pendingListener =
+      mPendingDirectTrackListeners.AppendElement();
+    pendingListener->mListener = listener;
+    pendingListener->mTrackID = aTrackID;
     return;
   }
   if (!isAudio && !isVideo) {
     STREAM_LOG(LogLevel::Warning, ("Source track for direct track listener %p is unknown",
                                    listener.get()));
     // It is not a video or audio track.
     MOZ_ASSERT(true);
     return;

--- a/dom/media/MediaStreamGraph.h
+++ b/dom/media/MediaStreamGraph.h
@@ -921,16 +921,19 @@ protected:
   // This time stamp will be updated in adding and blocked SourceMediaStream,
   // |AddStreamGraphThread| and |AdvanceTimeVaryingValuesToCurrentTime| in
   // particularly.
   TimeStamp mStreamTracksStartTimeStamp;
   nsTArray<TrackData> mUpdateTracks;
   nsTArray<TrackData> mPendingTracks;
   nsTArray<RefPtr<DirectMediaStreamListener>> mDirectListeners;
   nsTArray<TrackBound<DirectMediaStreamTrackListener>> mDirectTrackListeners;
+  // Direct track listeners that we don't have a track for yet. We'll move them
+  // to mDirectTrackListeners when their corresponding track becomes available.
+  nsTArray<TrackBound<DirectMediaStreamTrackListener>> mPendingDirectTrackListeners;
   bool mPullEnabled;
   bool mUpdateFinished;
   bool mNeedsMixing;
 };
 
 /**
  * The blocking mode decides how a track should be blocked in a MediaInputPort.
  */

--- a/dom/media/MediaStreamListener.h
+++ b/dom/media/MediaStreamListener.h
@@ -234,32 +234,27 @@ public:
   virtual void NotifyRealtimeTrackData(MediaStreamGraph* aGraph,
                                        StreamTime aTrackOffset,
                                        const MediaSegment& aMedia) {}
 
   /**
    * When a direct listener is processed for installation by the
    * MediaStreamGraph it will be notified with whether the installation was
    * successful or not. The results of this installation are the following:
-   * TRACK_NOT_FOUND_AT_SOURCE
-   *    We found the source stream of media data for this track, but the track
-   *    didn't exist. This should only happen if you try to install the listener
-   *    directly to a SourceMediaStream that doesn't contain the given TrackID.
    * STREAM_NOT_SUPPORTED
    *    While looking for the data source of this track, we found a MediaStream
    *    that is not a SourceMediaStream or a TrackUnionStream.
    * ALREADY_EXIST
    *    This DirectMediaStreamTrackListener already exists in the
    *    SourceMediaStream.
    * SUCCESS
    *    Installation was successful and this listener will start receiving
    *    NotifyRealtimeData on the next AppendToTrack().
    */
   enum class InstallationResult {
-    TRACK_NOT_FOUND_AT_SOURCE,
     TRACK_TYPE_NOT_SUPPORTED,
     STREAM_NOT_SUPPORTED,
     ALREADY_EXISTS,
     SUCCESS
   };
   virtual void NotifyDirectListenerInstalled(InstallationResult aResult) {}
   virtual void NotifyDirectListenerUninstalled() {}