diff --git a/content/media/MediaDecoderReader.h b/content/media/MediaDecoderReader.h
index d2bea4387a4a..713c275ef464 100644
--- a/content/media/MediaDecoderReader.h
+++ b/content/media/MediaDecoderReader.h
@@ -159,7 +159,6 @@ public:
   // Only used by WebMReader and MediaOmxReader for now, so stub here rather
   // than in every reader than inherits from MediaDecoderReader.
   virtual void NotifyDataArrived(const char* aBuffer, uint32_t aLength, int64_t aOffset) {}
-  virtual int64_t GetEvictionOffset(double aTime) { return -1; }
 
   virtual MediaQueue<AudioData>& AudioQueue() { return mAudioQueue; }
   virtual MediaQueue<VideoData>& VideoQueue() { return mVideoQueue; }
diff --git a/content/media/fmp4/MP4Reader.cpp b/content/media/fmp4/MP4Reader.cpp
index 541e3e9c0004..5f2f536ffa45 100644
--- a/content/media/fmp4/MP4Reader.cpp
+++ b/content/media/fmp4/MP4Reader.cpp
@@ -109,6 +109,7 @@ MP4Reader::MP4Reader(AbstractMediaDecoder* aDecoder)
   , mVideo("MP4 video decoder data", Preferences::GetUint("media.mp4-video-decode-ahead", 2))
   , mLastReportedNumDecodedFrames(0)
   , mLayersBackendType(layers::LayersBackend::LAYERS_NONE)
+  , mTimeRangesMonitor("MP4Reader::TimeRanges")
   , mDemuxerInitialized(false)
   , mIsEncrypted(false)
 {
@@ -768,36 +769,29 @@ MP4Reader::NotifyDataArrived(const char* aBuffer, uint32_t aLength,
 void
 MP4Reader::UpdateIndex()
 {
+  nsTArray<MediaByteRange> ranges;
+  nsTArray<Interval<Microseconds>> timeRanges;
+
   MediaResource* resource = mDecoder->GetResource();
   resource->Pin();
-  nsTArray<MediaByteRange> ranges;
   if (NS_SUCCEEDED(resource->GetCachedRanges(ranges))) {
-    mDemuxer->UpdateIndex(ranges);
+    mDemuxer->ConvertByteRangesToTime(ranges, &timeRanges);
   }
   resource->Unpin();
+
+  MonitorAutoLock mon(mTimeRangesMonitor);
+  mTimeRanges = timeRanges;
 }
 
-int64_t
-MP4Reader::GetEvictionOffset(double aTime)
-{
-  return mDemuxer->GetEvictionOffset(aTime * 1000000.0);
-}
 
 nsresult
 MP4Reader::GetBuffered(dom::TimeRanges* aBuffered, int64_t aStartTime)
 {
-  MediaResource* resource = mDecoder->GetResource();
-  resource->Pin();
-  nsTArray<MediaByteRange> ranges;
-  if (NS_SUCCEEDED(resource->GetCachedRanges(ranges))) {
-    nsTArray<Interval<Microseconds>> timeRanges;
-    mDemuxer->ConvertByteRangesToTime(ranges, &timeRanges);
-    for (size_t i = 0; i < timeRanges.Length(); i++) {
-      aBuffered->Add((timeRanges[i].start - aStartTime) / 1000000.0,
-                     (timeRanges[i].end - aStartTime) / 1000000.0);
-    }
+  MonitorAutoLock mon(mTimeRangesMonitor);
+  for (size_t i = 0; i < mTimeRanges.Length(); i++) {
+    aBuffered->Add((mTimeRanges[i].start - aStartTime) / 1000000.0,
+                   (mTimeRanges[i].end - aStartTime) / 1000000.0);
   }
-  resource->Unpin();
 
   return NS_OK;
 }
diff --git a/content/media/fmp4/MP4Reader.h b/content/media/fmp4/MP4Reader.h
index a073d3fbb4cf..6bc00ad18b31 100644
--- a/content/media/fmp4/MP4Reader.h
+++ b/content/media/fmp4/MP4Reader.h
@@ -55,8 +55,6 @@ public:
   virtual void NotifyDataArrived(const char* aBuffer, uint32_t aLength,
                                  int64_t aOffset) MOZ_OVERRIDE;
 
-  virtual int64_t GetEvictionOffset(double aTime) MOZ_OVERRIDE;
-
   virtual nsresult GetBuffered(dom::TimeRanges* aBuffered,
                                int64_t aStartTime) MOZ_OVERRIDE;
 
@@ -182,6 +180,8 @@ private:
   layers::LayersBackend mLayersBackendType;
 
   nsTArray<nsTArray<uint8_t>> mInitDataEncountered;
+  Monitor mTimeRangesMonitor;
+  nsTArray<mp4_demuxer::Interval<Microseconds>> mTimeRanges;
 
   // True if we've read the streams' metadata.
   bool mDemuxerInitialized;
diff --git a/content/media/mediasource/SubBufferDecoder.cpp b/content/media/mediasource/SubBufferDecoder.cpp
index 195997451cf9..9456dc40ae15 100644
--- a/content/media/mediasource/SubBufferDecoder.cpp
+++ b/content/media/mediasource/SubBufferDecoder.cpp
@@ -112,16 +112,11 @@ SubBufferDecoder::GetBuffered(dom::TimeRanges* aBuffered)
 int64_t
 SubBufferDecoder::ConvertToByteOffset(double aTime)
 {
-  int64_t readerOffset = mReader->GetEvictionOffset(aTime);
-  if (readerOffset >= 0) {
-    return readerOffset;
-  }
-
   // Uses a conversion based on (aTime/duration) * length.  For the
   // purposes of eviction this should be adequate since we have the
   // byte threshold as well to ensure data actually gets evicted and
   // we ensure we don't evict before the current playable point.
-  if (mMediaDuration <= 0) {
+  if (mMediaDuration == -1) {
     return -1;
   }
   int64_t length = GetResource()->GetLength();
diff --git a/media/libstagefright/binding/Index.cpp b/media/libstagefright/binding/Index.cpp
index e11f00985fef..eaed3b2c16f0 100644
--- a/media/libstagefright/binding/Index.cpp
+++ b/media/libstagefright/binding/Index.cpp
@@ -85,101 +85,67 @@ Index::Index(const stagefright::Vector<MediaSource::Indice>& aIndex,
 
 Index::~Index() {}
 
-void
-Index::UpdateMoofIndex(const nsTArray<MediaByteRange>& aByteRanges)
-{
-  if (!mMoofParser) {
-    return;
-  }
-
-  MonitorAutoLock mon(mMonitor);
-  mMoofParser->RebuildFragmentedIndex(aByteRanges);
-}
-
 void
 Index::ConvertByteRangesToTimeRanges(
   const nsTArray<MediaByteRange>& aByteRanges,
   nsTArray<Interval<Microseconds>>* aTimeRanges)
 {
-  MonitorAutoLock mon(mMonitor);
-
   RangeFinder rangeFinder(aByteRanges);
   nsTArray<Interval<Microseconds>> timeRanges;
 
-  nsTArray<nsTArray<stagefright::MediaSource::Indice>*> indexes;
+  nsTArray<stagefright::MediaSource::Indice> moofIndex;
+  nsTArray<stagefright::MediaSource::Indice>* index;
   if (mMoofParser) {
-    // We take the index out of the moof parser and move it into a local
-    // variable so we don't get concurrency issues. It gets freed when we
-    // exit this function.
-    for (int i = 0; i < mMoofParser->mMoofs.Length(); i++) {
-      Moof& moof = mMoofParser->mMoofs[i];
+    {
+      MonitorAutoLock mon(mMonitor);
+      mMoofParser->RebuildFragmentedIndex(aByteRanges);
 
-      // We need the entire moof in order to play anything
-      if (rangeFinder.Contains(moof.mRange)) {
-        if (rangeFinder.Contains(moof.mMdatRange)) {
+      // We take the index out of the moof parser and move it into a local
+      // variable so we don't get concurrency issues. It gets freed when we
+      // exit this function.
+      for (int i = 0; i < mMoofParser->mMoofs.Length(); i++) {
+        Moof& moof = mMoofParser->mMoofs[i];
+        if (rangeFinder.Contains(moof.mRange) &&
+            rangeFinder.Contains(moof.mMdatRange)) {
           timeRanges.AppendElements(moof.mTimeRanges);
         } else {
-          indexes.AppendElement(&moof.mIndex);
+          moofIndex.AppendElements(mMoofParser->mMoofs[i].mIndex);
         }
       }
     }
+    index = &moofIndex;
   } else {
-    indexes.AppendElement(&mIndex);
+    index = &mIndex;
   }
 
   bool hasSync = false;
-  for (size_t i = 0; i < indexes.Length(); i++) {
-    nsTArray<stagefright::MediaSource::Indice>* index = indexes[i];
-    for (size_t j = 0; j < index->Length(); j++) {
-      const MediaSource::Indice& indice = (*index)[j];
-      if (!rangeFinder.Contains(
-             MediaByteRange(indice.start_offset, indice.end_offset))) {
-        // We process the index in decode order so we clear hasSync when we hit
-        // a range that isn't buffered.
-        hasSync = false;
-        continue;
-      }
+  for (size_t i = 0; i < index->Length(); i++) {
+    const MediaSource::Indice& indice = (*index)[i];
+    if (!rangeFinder.Contains(MediaByteRange(indice.start_offset,
+                                             indice.end_offset))) {
+      // We process the index in decode order so we clear hasSync when we hit
+      // a range that isn't buffered.
+      hasSync = false;
+      continue;
+    }
 
-      hasSync |= indice.sync;
-      if (!hasSync) {
-        continue;
-      }
+    hasSync |= indice.sync;
+    if (!hasSync) {
+      continue;
+    }
 
-      Interval<Microseconds>::SemiNormalAppend(
-        timeRanges, Interval<Microseconds>(indice.start_composition,
-                                           indice.end_composition));
+    // This is an optimisation for when the file is decoded in composition
+    // order. It means that Normalise() below doesn't need to do a sort.
+    size_t s = timeRanges.Length();
+    if (s && timeRanges[s - 1].end == indice.start_composition) {
+      timeRanges[s - 1].end = indice.end_composition;
+    } else {
+      timeRanges.AppendElement(Interval<Microseconds>(indice.start_composition,
+                                                      indice.end_composition));
     }
   }
 
   // This fixes up when the compositon order differs from the byte range order
   Interval<Microseconds>::Normalize(timeRanges, aTimeRanges);
 }
-
-uint64_t
-Index::GetEvictionOffset(Microseconds aTime)
-{
-  uint64_t offset = std::numeric_limits<uint64_t>::max();
-  if (mMoofParser) {
-    // We need to keep the whole moof if we're keeping any of it because the
-    // parser doesn't keep parsed moofs.
-    for (int i = 0; i < mMoofParser->mMoofs.Length(); i++) {
-      Moof& moof = mMoofParser->mMoofs[i];
-
-      if (!moof.mTimeRanges.IsEmpty() && moof.mTimeRanges[0].end > aTime) {
-        offset = std::min(offset, uint64_t(std::min(moof.mRange.mStart,
-                                                    moof.mMdatRange.mStart)));
-      }
-    }
-  } else {
-    // We've already parsed and stored the moov so we don't need to keep it.
-    // All we need to keep is the sample data itself.
-    for (size_t i = 0; i < mIndex.Length(); i++) {
-      const MediaSource::Indice& indice = mIndex[i];
-      if (aTime >= indice.start_composition) {
-        offset = std::min(offset, indice.start_offset);
-      }
-    }
-  }
-  return offset;
-}
 }
diff --git a/media/libstagefright/binding/include/mp4_demuxer/Index.h b/media/libstagefright/binding/include/mp4_demuxer/Index.h
index eaeccfbba2be..618a905d4c75 100644
--- a/media/libstagefright/binding/include/mp4_demuxer/Index.h
+++ b/media/libstagefright/binding/include/mp4_demuxer/Index.h
@@ -22,11 +22,9 @@ public:
         Stream* aSource, uint32_t aTrackId);
   ~Index();
 
-  void UpdateMoofIndex(const nsTArray<mozilla::MediaByteRange>& aByteRanges);
   void ConvertByteRangesToTimeRanges(
     const nsTArray<mozilla::MediaByteRange>& aByteRanges,
     nsTArray<Interval<Microseconds>>* aTimeRanges);
-  uint64_t GetEvictionOffset(Microseconds aTime);
 
 private:
   mozilla::Monitor mMonitor;
diff --git a/media/libstagefright/binding/include/mp4_demuxer/Interval.h b/media/libstagefright/binding/include/mp4_demuxer/Interval.h
index 77f5f01fd025..61268acdb8a4 100644
--- a/media/libstagefright/binding/include/mp4_demuxer/Interval.h
+++ b/media/libstagefright/binding/include/mp4_demuxer/Interval.h
@@ -61,7 +61,7 @@ struct Interval
     }
     MOZ_ASSERT(aNormalized->IsEmpty());
 
-    nsTArray<Interval<T>> sorted;
+    nsTArray<Interval<T> > sorted;
     sorted = aIntervals;
     sorted.Sort(Compare());
 
@@ -81,9 +81,9 @@ struct Interval
     aNormalized->AppendElement(current);
   }
 
-  static void Intersection(const nsTArray<Interval<T>>& a0,
-                           const nsTArray<Interval<T>>& a1,
-                           nsTArray<Interval<T>>* aIntersection)
+  static void Intersection(const nsTArray<Interval<T> >& a0,
+                           const nsTArray<Interval<T> >& a1,
+                           nsTArray<Interval<T> >* aIntersection)
   {
     MOZ_ASSERT(IsNormalized(a0));
     MOZ_ASSERT(IsNormalized(a1));
@@ -106,7 +106,7 @@ struct Interval
     }
   }
 
-  static bool IsNormalized(const nsTArray<Interval<T>>& aIntervals)
+  static bool IsNormalized(const nsTArray<Interval<T> >& aIntervals)
   {
     for (size_t i = 1; i < aIntervals.Length(); i++) {
       if (aIntervals[i - 1].end >= aIntervals[i].start) {
diff --git a/media/libstagefright/binding/include/mp4_demuxer/mp4_demuxer.h b/media/libstagefright/binding/include/mp4_demuxer/mp4_demuxer.h
index 0105b9c97b32..72fa4c6690c8 100644
--- a/media/libstagefright/binding/include/mp4_demuxer/mp4_demuxer.h
+++ b/media/libstagefright/binding/include/mp4_demuxer/mp4_demuxer.h
@@ -59,13 +59,9 @@ public:
   const AudioDecoderConfig& AudioConfig() { return mAudioConfig; }
   const VideoDecoderConfig& VideoConfig() { return mVideoConfig; }
 
-  void UpdateIndex(const nsTArray<mozilla::MediaByteRange>& aByteRanges);
-
   void ConvertByteRangesToTime(
     const nsTArray<mozilla::MediaByteRange>& aByteRanges,
-    nsTArray<Interval<Microseconds>>* aIntervals);
-
-  int64_t GetEvictionOffset(Microseconds aTime);
+    nsTArray<Interval<Microseconds> >* aIntervals);
 
 private:
   AudioDecoderConfig mAudioConfig;
diff --git a/media/libstagefright/binding/mp4_demuxer.cpp b/media/libstagefright/binding/mp4_demuxer.cpp
index 105ede19b356..5daf7dd75bf9 100644
--- a/media/libstagefright/binding/mp4_demuxer.cpp
+++ b/media/libstagefright/binding/mp4_demuxer.cpp
@@ -12,7 +12,6 @@
 
 #include <stdint.h>
 #include <algorithm>
-#include <limits>
 
 using namespace stagefright;
 
@@ -195,14 +194,6 @@ MP4Demuxer::DemuxVideoSample()
   return sample.forget();
 }
 
-void
-MP4Demuxer::UpdateIndex(const nsTArray<mozilla::MediaByteRange>& aByteRanges)
-{
-  for (int i = 0; i < mPrivate->mIndexes.Length(); i++) {
-    mPrivate->mIndexes[i]->UpdateMoofIndex(aByteRanges);
-  }
-}
-
 void
 MP4Demuxer::ConvertByteRangesToTime(
   const nsTArray<mozilla::MediaByteRange>& aByteRanges,
@@ -224,18 +215,4 @@ MP4Demuxer::ConvertByteRangesToTime(
   }
 }
 
-int64_t
-MP4Demuxer::GetEvictionOffset(Microseconds aTime)
-{
-  if (mPrivate->mIndexes.IsEmpty()) {
-    return 0;
-  }
-
-  uint64_t offset = std::numeric_limits<uint64_t>::max();
-  for (int i = 0; i < mPrivate->mIndexes.Length(); i++) {
-    offset = std::min(offset, mPrivate->mIndexes[i]->GetEvictionOffset(aTime));
-  }
-  return offset;
-}
-
 } // namespace mp4_demuxer