--- a/dom/media/MediaSegment.h
+++ b/dom/media/MediaSegment.h
@@ -411,17 +411,17 @@ protected:
     }
     mChunks.AppendElements(Move(aSource->mChunks));
   }
 
   void AppendSliceInternal(const MediaSegmentBase<C, Chunk>& aSource,
                            StreamTime aStart, StreamTime aEnd)
   {
     MOZ_ASSERT(aStart <= aEnd, "Endpoints inverted");
-    NS_WARN_IF_FALSE(aStart >= 0 && aEnd <= aSource.mDuration, "Slice out of range");
+    NS_ASSERTION(aStart >= 0 && aEnd <= aSource.mDuration, "Slice out of range");
     mDuration += aEnd - aStart;
     StreamTime offset = 0;
     for (uint32_t i = 0; i < aSource.mChunks.Length() && offset < aEnd; ++i) {
       const Chunk& c = aSource.mChunks[i];
       StreamTime start = std::max(aStart, offset);
       StreamTime nextOffset = offset + c.GetDuration();
       StreamTime end = std::min(aEnd, nextOffset);
       if (start < end) {

--- a/dom/media/MediaStreamGraph.cpp
+++ b/dom/media/MediaStreamGraph.cpp
@@ -1434,19 +1434,19 @@ MediaStreamGraphImpl::Process()
 #endif
           // Since an AudioNodeStream is present, go ahead and
           // produce audio block by block for all the rest of the streams.
           ProduceDataForStreamsBlockByBlock(i, n->SampleRate());
           doneAllProducing = true;
         } else {
           ps->ProcessInput(mProcessedTime, mStateComputedTime,
                            ProcessedMediaStream::ALLOW_FINISH);
-          NS_WARN_IF_FALSE(stream->mTracks.GetEnd() >=
-                           GraphTimeToStreamTimeWithBlocking(stream, mStateComputedTime),
-                           "Stream did not produce enough data");
+          NS_ASSERTION(stream->mTracks.GetEnd() >=
+                       GraphTimeToStreamTimeWithBlocking(stream, mStateComputedTime),
+                       "Stream did not produce enough data");
         }
       }
     }
     NotifyHasCurrentData(stream);
     // Only playback audio and video in real-time mode
     if (mRealtime) {
       CreateOrDestroyAudioStreams(stream);
       if (CurrentDriver()->AsAudioCallbackDriver()) {

--- a/dom/media/StreamTracks.h
+++ b/dom/media/StreamTracks.h
@@ -26,17 +26,17 @@ inline bool IsTrackIDExplicit(const Trac
 }
 
 inline TrackTicks RateConvertTicksRoundDown(TrackRate aOutRate,
                                             TrackRate aInRate,
                                             TrackTicks aTicks)
 {
   NS_ASSERTION(0 < aOutRate && aOutRate <= TRACK_RATE_MAX, "Bad out rate");
   NS_ASSERTION(0 < aInRate && aInRate <= TRACK_RATE_MAX, "Bad in rate");
-  NS_WARN_IF_FALSE(0 <= aTicks && aTicks <= TRACK_TICKS_MAX, "Bad ticks"); // bug 957691
+  NS_ASSERTION(0 <= aTicks && aTicks <= TRACK_TICKS_MAX, "Bad ticks");
   return (aTicks * aOutRate) / aInRate;
 }
 inline TrackTicks RateConvertTicksRoundUp(TrackRate aOutRate,
                                           TrackRate aInRate, TrackTicks aTicks)
 {
   NS_ASSERTION(0 < aOutRate && aOutRate <= TRACK_RATE_MAX, "Bad out rate");
   NS_ASSERTION(0 < aInRate && aInRate <= TRACK_RATE_MAX, "Bad in rate");
   NS_ASSERTION(0 <= aTicks && aTicks <= TRACK_TICKS_MAX, "Bad ticks");