--- a/dom/media/TrackUnionStream.cpp
+++ b/dom/media/TrackUnionStream.cpp
@@ -306,28 +306,28 @@ TrackUnionStream::TrackUnionStream()
       interval.mEnd = std::min(interval.mEnd, aTo);
       StreamTime inputEnd = source->GraphTimeToStreamTimeWithBlocking(interval.mEnd);
       StreamTime inputTrackEndPoint = STREAM_TIME_MAX;
 
       if (aInputTrack->IsEnded() &&
           aInputTrack->GetEnd() <= inputEnd) {
         inputTrackEndPoint = aInputTrack->GetEnd();
         *aOutputTrackFinished = true;
+        break;
       }
 
       if (interval.mStart >= interval.mEnd) {
         break;
       }
       StreamTime ticks = interval.mEnd - interval.mStart;
       next = interval.mEnd;
 
       StreamTime outputStart = outputTrack->GetEnd();
 
       if (interval.mInputIsBlocked) {
-        // Maybe the input track ended?
         segment->AppendNullData(ticks);
         STREAM_LOG(LogLevel::Verbose, ("TrackUnionStream %p appending %lld ticks of null data to track %d",
                    this, (long long)ticks, outputTrack->GetID()));
       } else if (InMutedCycle()) {
         segment->AppendNullData(ticks);
       } else {
         if (source->IsSuspended()) {
           segment->AppendNullData(aTo - aFrom);