diff --git a/mkvmuxer.cpp b/mkvmuxer.cpp
index fb6c9c3..4cf97d5 100644
--- a/mkvmuxer.cpp
+++ b/mkvmuxer.cpp
@@ -131,7 +131,9 @@ Frame::Frame()
       length_(0),
       track_number_(0),
       timestamp_(0),
-      discard_padding_(0) {}
+      discard_padding_(0),
+      reference_block_timestamp_(0),
+      reference_block_timestamp_set_(false) {}
 
 Frame::~Frame() {
   delete[] frame_;
@@ -204,6 +206,9 @@ bool Frame::IsValid() const {
   if (track_number_ == 0 || track_number_ > kMaxTrackNumber) {
     return false;
   }
+  if (!CanBeSimpleBlock() && !is_key_ && !reference_block_timestamp_set_) {
+    return false;
+  }
   return true;
 }
 
@@ -211,6 +216,11 @@ bool Frame::CanBeSimpleBlock() const {
   return additional_ == NULL && discard_padding_ == 0 && duration_ == 0;
 }
 
+void Frame::set_reference_block_timestamp(int64 reference_block_timestamp) {
+  reference_block_timestamp_ = reference_block_timestamp;
+  reference_block_timestamp_set_ = true;
+}
+
 ///////////////////////////////////////////////////////////////
 //
 // CuePoint Class
@@ -2426,6 +2436,20 @@ bool Segment::AddGenericFrame(const Frame* frame) {
   if (!cluster)
     return false;
 
+  // If the Frame is not a SimpleBlock, then set the reference_block_timestamp
+  // if it is not set already.
+  bool frame_created = false;
+  if (!frame->CanBeSimpleBlock() && !frame->is_key() &&
+      !frame->reference_block_timestamp_set()) {
+    Frame* const new_frame = new (std::nothrow) Frame();
+    if (!new_frame->CopyFrom(*frame))
+      return false;
+    new_frame->set_reference_block_timestamp(
+        last_track_timestamp_[frame->track_number() - 1]);
+    frame = new_frame;
+    frame_created = true;
+  }
+
   if (!cluster->AddFrame(frame))
     return false;
 
@@ -2435,8 +2459,12 @@ bool Segment::AddGenericFrame(const Frame* frame) {
   }
 
   last_timestamp_ = frame->timestamp();
+  last_track_timestamp_[frame->track_number() - 1] = frame->timestamp();
   last_block_duration_ = frame->duration();
 
+  if (frame_created)
+    delete frame;
+
   return true;
 }
 
@@ -2947,8 +2975,10 @@ int Segment::WriteFramesAll() {
         return -1;
     }
 
-    if (frame_timestamp > last_timestamp_)
+    if (frame_timestamp > last_timestamp_) {
       last_timestamp_ = frame_timestamp;
+      last_track_timestamp_[frame->track_number() - 1] = frame_timestamp;
+    }
 
     delete frame;
     frame = NULL;
@@ -3010,8 +3040,10 @@ bool Segment::WriteFramesLessThan(uint64 timestamp) {
       }
 
       ++shift_left;
-      if (frame_timestamp > last_timestamp_)
+      if (frame_timestamp > last_timestamp_) {
         last_timestamp_ = frame_timestamp;
+        last_track_timestamp_[frame_prev->track_number() - 1] = frame_timestamp;
+      }
 
       delete frame_prev;
     }
diff --git a/mkvmuxer.hpp b/mkvmuxer.hpp
index cf93436..900b48b 100644
--- a/mkvmuxer.hpp
+++ b/mkvmuxer.hpp
@@ -23,6 +23,8 @@ namespace mkvmuxer {
 class MkvWriter;
 class Segment;
 
+const uint64 kMaxTrackNumber = 126;
+
 ///////////////////////////////////////////////////////////////
 // Interface used by the mkvmuxer to write out the Mkv data.
 class IMkvWriter {
@@ -108,6 +110,11 @@ class Frame {
     discard_padding_ = discard_padding;
   }
   int64 discard_padding() const { return discard_padding_; }
+  void set_reference_block_timestamp(int64 reference_block_timestamp);
+  int64 reference_block_timestamp() const { return reference_block_timestamp_; }
+  bool reference_block_timestamp_set() const {
+    return reference_block_timestamp_set_;
+  }
 
  private:
   // Id of the Additional data.
@@ -140,6 +147,12 @@ class Frame {
   // Discard padding for the frame.
   int64 discard_padding_;
 
+  // Reference block timestamp.
+  int64 reference_block_timestamp_;
+
+  // Flag indicating if |reference_block_timestamp_| has been set.
+  bool reference_block_timestamp_set_;
+
   LIBWEBM_DISALLOW_COPY_AND_ASSIGN(Frame);
 };
 
@@ -1312,6 +1325,9 @@ class Segment {
   // Last timestamp in nanoseconds added to a cluster.
   uint64 last_timestamp_;
 
+  // Last timestamp in nanoseconds by track number added to a cluster.
+  uint64 last_track_timestamp_[kMaxTrackNumber];
+
   // Maximum time in nanoseconds for a cluster duration. This variable is a
   // guideline and some clusters may have a longer duration. Default is 30
   // seconds.
diff --git a/mkvmuxerutil.cpp b/mkvmuxerutil.cpp
index 5d34db4..6d55ed8 100644
--- a/mkvmuxerutil.cpp
+++ b/mkvmuxerutil.cpp
@@ -36,7 +36,7 @@ namespace {
 const int kDateElementSize = 8;
 
 uint64 WriteBlock(IMkvWriter* writer, const Frame* const frame, int64 timecode,
-                  uint64 duration) {
+                  uint64 timecode_scale) {
   uint64 block_additional_elem_size = 0;
   uint64 block_addid_elem_size = 0;
   uint64 block_more_payload_size = 0;
@@ -66,6 +66,15 @@ uint64 WriteBlock(IMkvWriter* writer, const Frame* const frame, int64 timecode,
         EbmlElementSize(kMkvDiscardPadding, frame->discard_padding());
   }
 
+  const uint64 reference_block_timestamp =
+      frame->reference_block_timestamp() / timecode_scale;
+  uint64 reference_block_elem_size = 0;
+  if (!frame->is_key()) {
+    reference_block_elem_size =
+        EbmlElementSize(kMkvReferenceBlock, reference_block_timestamp);
+  }
+
+  const uint64 duration = frame->duration() / timecode_scale;
   uint64 block_duration_elem_size = 0;
   if (duration > 0)
     block_duration_elem_size = EbmlElementSize(kMkvBlockDuration, duration);
@@ -76,7 +85,7 @@ uint64 WriteBlock(IMkvWriter* writer, const Frame* const frame, int64 timecode,
 
   const uint64 block_group_payload_size =
       block_elem_size + block_additions_elem_size + block_duration_elem_size +
-      discard_padding_elem_size;
+      discard_padding_elem_size + reference_block_elem_size;
 
   if (!WriteEbmlMasterElement(writer, kMkvBlockGroup,
                               block_group_payload_size)) {
@@ -92,10 +101,8 @@ uint64 WriteBlock(IMkvWriter* writer, const Frame* const frame, int64 timecode,
   if (SerializeInt(writer, timecode, 2))
     return 0;
 
-  uint64 flags = 0;
-  if (frame->is_key())
-    flags |= 0x80;
-  if (SerializeInt(writer, flags, 1))
+  // For a Block, flags is always 0.
+  if (SerializeInt(writer, 0, 1))
     return 0;
 
   if (writer->Write(frame->frame(), static_cast<uint32>(frame->length())))
@@ -119,18 +126,15 @@ uint64 WriteBlock(IMkvWriter* writer, const Frame* const frame, int64 timecode,
     }
   }
 
-  if (frame->discard_padding() != 0) {
-    if (WriteID(writer, kMkvDiscardPadding))
-      return 0;
+  if (frame->discard_padding() != 0 &&
+      !WriteEbmlElement(writer, kMkvDiscardPadding, frame->discard_padding())) {
+    return false;
+  }
 
-    const uint64 size = GetIntSize(frame->discard_padding());
-    if (WriteUInt(writer, size))
-      return false;
-
-    if (SerializeInt(writer, frame->discard_padding(),
-                     static_cast<int32>(size))) {
-      return false;
-    }
+  if (!frame->is_key() &&
+      !WriteEbmlElement(writer, kMkvReferenceBlock,
+                        reference_block_timestamp)) {
+    return false;
   }
 
   if (duration > 0 && !WriteEbmlElement(writer, kMkvBlockDuration, duration)) {
@@ -440,6 +444,23 @@ bool WriteEbmlElement(IMkvWriter* writer, uint64 type, uint64 value) {
   return true;
 }
 
+bool WriteEbmlElement(IMkvWriter* writer, uint64 type, int64 value) {
+  if (!writer)
+    return false;
+
+  if (WriteID(writer, type))
+    return 0;
+
+  const uint64 size = GetIntSize(value);
+  if (WriteUInt(writer, size))
+    return false;
+
+  if (SerializeInt(writer, value, static_cast<int32>(size)))
+    return false;
+
+  return true;
+}
+
 bool WriteEbmlElement(IMkvWriter* writer, uint64 type, float value) {
   if (!writer)
     return false;
@@ -524,7 +545,7 @@ uint64 WriteFrame(IMkvWriter* writer, const Frame* const frame,
   return frame->CanBeSimpleBlock()
              ? WriteSimpleBlock(writer, frame, relative_timecode)
              : WriteBlock(writer, frame, relative_timecode,
-                          frame->duration() / cluster->timecode_scale());
+                          cluster->timecode_scale());
 }
 
 uint64 WriteVoidElement(IMkvWriter* writer, uint64 size) {
diff --git a/mkvmuxerutil.hpp b/mkvmuxerutil.hpp
index 865d42a..e318576 100644
--- a/mkvmuxerutil.hpp
+++ b/mkvmuxerutil.hpp
@@ -18,7 +18,6 @@ class IMkvWriter;
 
 const uint64 kEbmlUnknownValue = 0x01FFFFFFFFFFFFFFULL;
 const int64 kMaxBlockTimecode = 0x07FFFLL;
-const uint64 kMaxTrackNumber = 126;
 
 // Writes out |value| in Big Endian order. Returns 0 on success.
 int32 SerializeInt(IMkvWriter* writer, int64 value, int32 size);
@@ -54,6 +53,7 @@ int32 WriteID(IMkvWriter* writer, uint64 type);
 
 // Output an Mkv non-master element. Returns true if the element was written.
 bool WriteEbmlElement(IMkvWriter* writer, uint64 type, uint64 value);
+bool WriteEbmlElement(IMkvWriter* writer, uint64 type, int64 value);
 bool WriteEbmlElement(IMkvWriter* writer, uint64 type, float value);
 bool WriteEbmlElement(IMkvWriter* writer, uint64 type, const char* value);
 bool WriteEbmlElement(IMkvWriter* writer, uint64 type, const uint8* value,