diff --git a/src/BlockFile.cpp b/src/BlockFile.cpp
index ebe99870f..cd17b73b4 100644
--- a/src/BlockFile.cpp
+++ b/src/BlockFile.cpp
@@ -101,7 +101,6 @@ ArrayOf<char> BlockFile::fullSummary;
 /// @param samples  The number of samples this BlockFile contains.
 BlockFile::BlockFile(wxFileNameWrapper &&fileName, sampleCount samples):
    mLockCount(0),
-   mRefCount(1),
    mFileName(std::move(fileName)),
    mLen(samples),
    mSummaryInfo(samples)
@@ -165,28 +164,6 @@ bool BlockFile::IsLocked()
    return mLockCount > 0;
 }
 
-/// Increases the reference count of this block by one.  Only
-/// DirManager should call this method.
-void BlockFile::Ref() const
-{
-   mRefCount++;
-   BLOCKFILE_DEBUG_OUTPUT("Ref", mRefCount);
-}
-
-/// Decreases the reference count of this block by one.  If this
-/// causes the count to become zero, deletes the associated disk
-/// file and deletes this object
-bool BlockFile::Deref() const
-{
-   mRefCount--;
-   BLOCKFILE_DEBUG_OUTPUT("Deref", mRefCount);
-   if (mRefCount <= 0) {
-      delete this;
-      return true;
-   } else
-      return false;
-}
-
 /// Get a buffer containing a summary block describing this sample
 /// data.  This must be called by derived classes when they
 /// are constructed, to allow them to construct their summary data,
diff --git a/src/BlockFile.h b/src/BlockFile.h
index 9b08d6cb5..9086790e7 100644
--- a/src/BlockFile.h
+++ b/src/BlockFile.h
@@ -44,15 +44,12 @@ class SummaryInfo {
 
 
 class BlockFile;
+using BlockFilePtr = std::shared_ptr<BlockFile>;
 
-// to do: use shared_ptr instead
-using BlockFilePtr = BlockFile *;
-
-// to do: make this a synonym for make_shared
 template< typename Result, typename... Args >
-inline Result *make_blockfile (Args && ... args)
+inline std::shared_ptr< Result > make_blockfile (Args && ... args)
 {
-   return new Result( std::forward< Args > ( args )... );
+   return std::make_shared< Result > ( std::forward< Args > ( args )... );
 }
 
 class PROFILE_DLL_API BlockFile /* not final, abstract */ {
@@ -168,17 +165,6 @@ class PROFILE_DLL_API BlockFile /* not final, abstract */ {
 
  private:
 
-   friend class DirManager;
-   friend class AudacityApp;
-   //needed for Ref/Deref access.
-   friend class ODComputeSummaryTask;
-   friend class ODDecodeTask;
-   friend class ODPCMAliasBlockFile;
-
-   virtual void Ref() const;
-   virtual bool Deref() const;
-   virtual int RefCount(){return mRefCount;}
-
  protected:
    /// Calculate summary data for the given sample data
    /// Overrides have differing details of memory management
@@ -199,7 +185,6 @@ class PROFILE_DLL_API BlockFile /* not final, abstract */ {
 
  private:
    int mLockCount;
-   mutable int mRefCount;
 
    static ArrayOf<char> fullSummary;
 
diff --git a/src/Dependencies.cpp b/src/Dependencies.cpp
index 81b975261..5331d9b2c 100644
--- a/src/Dependencies.cpp
+++ b/src/Dependencies.cpp
@@ -94,10 +94,6 @@ static void ReplaceBlockFiles(AudacityProject *project,
       const auto src = &*f;
       if (hash.count( src ) > 0) {
          const auto &dst = hash[src];
-
-         dirManager->Deref(src);
-         dirManager->Ref(dst);
-
          f = dst;
       }
    }
@@ -223,11 +219,6 @@ static void RemoveDependencies(AudacityProject *project,
    // However, that didn't actually change any references to these
    // blockfiles in the Sequences, so we do that next...
    ReplaceBlockFiles(project, blockFileHash);
-
-   // Subtract one from reference count of NEW block files; they're
-   // now all referenced the proper number of times by the Sequences
-   for (const auto &pair : blockFileHash)
-      dirManager->Deref(pair.second);
 }
 
 //
diff --git a/src/DirManager.cpp b/src/DirManager.cpp
index 187431a3b..a95b8eae0 100644
--- a/src/DirManager.cpp
+++ b/src/DirManager.cpp
@@ -454,7 +454,7 @@ bool DirManager::SetProject(wxString& newProjPath, wxString& newProjName, const
       int count = 0;
       while ((iter != mBlockFileHash.end()) && success)
       {
-         BlockFilePtr b = iter->second;
+         BlockFilePtr b = iter->second.lock();
 
          if (!b)
             continue;
@@ -486,7 +486,7 @@ bool DirManager::SetProject(wxString& newProjPath, wxString& newProjName, const
          BlockHash::iterator iter = mBlockFileHash.begin();
          while (iter != mBlockFileHash.end())
          {
-            BlockFilePtr b = iter->second;
+            BlockFilePtr b = iter->second.lock();
 
             if (!b)
                continue;
@@ -726,7 +726,7 @@ auto DirManager::GetBalanceInfo() -> BalanceInfo &
       auto it = mBlockFileHash.begin(), end = mBlockFileHash.end();
       while (it != end)
       {
-         BlockFilePtr ptr { it->second };
+         BlockFilePtr ptr { it->second.lock() };
          if (!ptr) {
             auto name = it->first;
             mBlockFileHash.erase( it++ );
@@ -1006,7 +1006,7 @@ bool DirManager::ContainsBlockFile(const BlockFile *b) const
    BlockHash::const_iterator it = mBlockFileHash.find(result.name.GetName());
    if (it == mBlockFileHash.end())
       return false;
-   BlockFilePtr ptr = it->second;
+   BlockFilePtr ptr = it->second.lock();
    return ptr && (b == &*ptr);
 }
 
@@ -1015,7 +1015,7 @@ bool DirManager::ContainsBlockFile(const wxString &filepath) const
    // check what the hash returns in case the blockfile is from a different project
    BlockHash::const_iterator it = mBlockFileHash.find(filepath);
    return it != mBlockFileHash.end() &&
-      BlockFilePtr{ it->second };
+      BlockFilePtr{ it->second.lock() };
 }
 
 // Adds one to the reference count of the block file,
@@ -1027,7 +1027,6 @@ BlockFilePtr DirManager::CopyBlockFile(const BlockFilePtr &b)
    const auto &fn = result.name;
 
    if (!b->IsLocked()) {
-      b->Ref();
       //mchinen:July 13 2009 - not sure about this, but it needs to be added to the hash to be able to save if not locked.
       //note that this shouldn't hurt mBlockFileHash's that already contain the filename, since it should just overwrite.
       //but it's something to watch out for.
@@ -1148,7 +1147,6 @@ bool DirManager::HandleXMLTag(const wxChar *tag, const wxChar **attrs)
       // See http://bugzilla.audacityteam.org/show_bug.cgi?id=451#c13.
       // Lock pBlockFile so that the ~BlockFile() will not DELETE the file on disk.
       pBlockFile->Lock();
-      delete pBlockFile;
       return false;
    }
    else
@@ -1162,7 +1160,7 @@ bool DirManager::HandleXMLTag(const wxChar *tag, const wxChar **attrs)
 
    wxString name = target->GetFileName().name.GetName();
    auto &wRetrieved = mBlockFileHash[name];
-   BlockFilePtr retrieved = wRetrieved;
+   BlockFilePtr retrieved = wRetrieved.lock();
    if (retrieved) {
       // Lock it in order to DELETE it safely, i.e. without having
       // it DELETE the file, too...
@@ -1260,38 +1258,6 @@ bool DirManager::CopyToNewProjectDirectory(BlockFile *f)
    return MoveOrCopyToNewProjectDirectory(f, true);
 }
 
-void DirManager::Ref(BlockFile * f)
-{
-   f->Ref();
-   //printf("Ref(%d): %s\n",
-   //       f->mRefCount,
-   //       (const char *)f->mFileName.GetFullPath().mb_str());
-}
-
-int DirManager::GetRefCount(BlockFile * f)
-{
-   return f->mRefCount;
-}
-
-void DirManager::Deref(BlockFile * f)
-{
-   const wxString theFileName = f->GetFileName().name.GetName();
-
-   //printf("Deref(%d): %s\n",
-   //       f->mRefCount-1,
-   //       (const char *)f->mFileName.GetFullPath().mb_str());
-
-   if (f->Deref()) {
-      // If Deref() returned true, the reference count reached zero
-      // and this block is no longer needed.  Remove it from the hash
-      // table.
-
-      mBlockFileHash.erase(theFileName);
-      BalanceInfoDel(theFileName);
-
-   }
-}
-
 bool DirManager::EnsureSafeFilename(const wxFileName &fName)
 {
    // Quick check: If it's not even in our alias list,
@@ -1352,7 +1318,7 @@ bool DirManager::EnsureSafeFilename(const wxFileName &fName)
    BlockHash::iterator iter = mBlockFileHash.begin();
    while (iter != mBlockFileHash.end())
    {
-      BlockFilePtr b = iter->second;
+      BlockFilePtr b = iter->second.lock();
 
       if (!b)
          continue;
@@ -1395,7 +1361,7 @@ bool DirManager::EnsureSafeFilename(const wxFileName &fName)
          BlockHash::iterator iter = mBlockFileHash.begin();
          while (iter != mBlockFileHash.end())
          {
-            BlockFilePtr b = iter->second;
+            BlockFilePtr b = iter->second.lock();
 
             if (!b)
                continue;
@@ -1423,7 +1389,7 @@ bool DirManager::EnsureSafeFilename(const wxFileName &fName)
          BlockHash::iterator iter = mBlockFileHash.begin();
          while (iter != mBlockFileHash.end())
          {
-            BlockFilePtr b = iter->second;
+            BlockFilePtr b = iter->second.lock();
 
             if (!b)
                continue;
@@ -1558,7 +1524,7 @@ _("Project check of \"%s\" folder \
          while (iter != missingAliasedFileAUFHash.end())
          {
             // This type cast is safe. We checked that it's an alias block file earlier.
-            BlockFilePtr b = iter->second;
+            BlockFilePtr b = iter->second.lock();
 
             wxASSERT(b);
             if (!b)
@@ -1625,7 +1591,7 @@ _("Project check of \"%s\" folder \
          BlockHash::iterator iter = missingAUFHash.begin();
          while (iter != missingAUFHash.end())
          {
-            BlockFilePtr b = iter->second;
+            BlockFilePtr b = iter->second.lock();
 
             wxASSERT(b);
             if (!b)
@@ -1689,7 +1655,7 @@ _("Project check of \"%s\" folder \
          BlockHash::iterator iter = missingAUHash.begin();
          while (iter != missingAUHash.end())
          {
-            BlockFilePtr b = iter->second;
+            BlockFilePtr b = iter->second.lock();
 
             wxASSERT(b);
             if (!b)
@@ -1801,7 +1767,7 @@ void DirManager::FindMissingAliasedFiles(
    while (iter != mBlockFileHash.end())
    {
       wxString key = iter->first;   // file name and extension
-      BlockFilePtr b = iter->second;
+      BlockFilePtr b = iter->second.lock();
 
       if (!b)
          continue;
@@ -1841,7 +1807,7 @@ void DirManager::FindMissingAUFs(
    while (iter != mBlockFileHash.end())
    {
       const wxString &key = iter->first;
-      BlockFilePtr b = iter->second;
+      BlockFilePtr b = iter->second.lock();
 
       if (!b)
          continue;
@@ -1871,7 +1837,7 @@ void DirManager::FindMissingAUs(
    while (iter != mBlockFileHash.end())
    {
       const wxString &key = iter->first;
-      BlockFilePtr b = iter->second;
+      BlockFilePtr b = iter->second.lock();
 
       if (!b)
          continue;
@@ -1975,7 +1941,7 @@ void DirManager::FillBlockfilesCache()
    iter = mBlockFileHash.begin();
    while (iter != mBlockFileHash.end())
    {
-      BlockFilePtr b = iter->second;
+      BlockFilePtr b = iter->second.lock();
 
       if (!b)
          continue;
@@ -1995,7 +1961,7 @@ void DirManager::FillBlockfilesCache()
    int current = 0;
    while (iter != mBlockFileHash.end())
    {
-      BlockFilePtr b = iter->second;
+      BlockFilePtr b = iter->second.lock();
 
       if (!b)
          continue;
@@ -2020,7 +1986,7 @@ void DirManager::WriteCacheToDisk()
    iter = mBlockFileHash.begin();
    while (iter != mBlockFileHash.end())
    {
-      BlockFilePtr b = iter->second;
+      BlockFilePtr b = iter->second.lock();
 
       if (!b)
          continue;
@@ -2040,7 +2006,7 @@ void DirManager::WriteCacheToDisk()
    int current = 0;
    while (iter != mBlockFileHash.end())
    {
-      BlockFilePtr b = iter->second;
+      BlockFilePtr b = iter->second.lock();
 
       if (!b)
          continue;
diff --git a/src/DirManager.h b/src/DirManager.h
index ed1e46d95..4833870a8 100644
--- a/src/DirManager.h
+++ b/src/DirManager.h
@@ -34,9 +34,10 @@ class SequenceTest;
 WX_DECLARE_HASH_MAP(int, int, wxIntegerHash, wxIntegerEqual, DirHash);
 
 class BlockFile;
-using BlockFilePtr = BlockFile *;
+using BlockFilePtr = std::shared_ptr<BlockFile>;
 
-WX_DECLARE_HASH_MAP(wxString, BlockFilePtr, wxStringHash, wxStringEqual, BlockHash);
+WX_DECLARE_HASH_MAP(wxString, std::weak_ptr<BlockFile>, wxStringHash,
+                    wxStringEqual, BlockHash);
 
 wxMemorySize GetFreeMemory();
 
@@ -101,12 +102,6 @@ class PROFILE_DLL_API DirManager final : public XMLTagHandler {
 
    bool EnsureSafeFilename(const wxFileName &fName);
 
-   void Ref(BlockFile * f);
-   void Deref(BlockFile * f);
-
-   // For debugging only
-   int GetRefCount(BlockFile * f);
-
    void SetLoadingTarget(BlockArray *pArray, unsigned idx)
    {
       mLoadingTarget = pArray;
diff --git a/src/MemoryX.h b/src/MemoryX.h
index 6cb6f89d4..2d053e6e9 100644
--- a/src/MemoryX.h
+++ b/src/MemoryX.h
@@ -34,6 +34,7 @@ using std::isinf;
 namespace std {
    using std::tr1::shared_ptr;
    using std::tr1::weak_ptr;
+   using std::tr1::static_pointer_cast;
    using std::tr1::remove_reference;
 
    template<typename X> struct default_delete
diff --git a/src/Sequence.cpp b/src/Sequence.cpp
index 16b2cdfa8..ebb5b9621 100644
--- a/src/Sequence.cpp
+++ b/src/Sequence.cpp
@@ -75,19 +75,6 @@ Sequence::Sequence(const Sequence &orig, const std::shared_ptr<DirManager> &proj
 
 Sequence::~Sequence()
 {
-   DerefAllFiles();
-}
-
-void Sequence::DerefAllFiles()
-{
-   for (size_t i = 0, nn = mBlock.size(); i < nn; i++)
-   {
-      BlockFile *& pOldFile = mBlock[i].f;
-      if (pOldFile) {
-         mDirManager->Deref(pOldFile);
-         pOldFile = NULL;
-      }
-   }
 }
 
 sampleCount Sequence::GetMaxBlockSize() const
@@ -210,8 +197,6 @@ bool Sequence::ConvertToSampleFormat(sampleFormat format, bool* pbChanged)
       // Invalidate all the old, non-aliased block files.
       // Aliased files will be converted at save, per comment above.
 
-      DerefAllFiles();
-
       // Replace with NEW blocks.
       mBlock.swap(newBlockArray);
    }
@@ -550,7 +535,6 @@ bool Sequence::Paste(sampleCount s, const Sequence *src)
       auto file =
          mDirManager->NewSimpleBlockFile(buffer.ptr(), largerBlockLen, mSampleFormat);
 
-      mDirManager->Deref(block.f);
       block.f = file;
 
       for (unsigned int i = b + 1; i < numBlocks; i++)
@@ -635,8 +619,6 @@ bool Sequence::Paste(sampleCount s, const Sequence *src)
       Blockify(newBlock, s + lastStart, sampleBuffer.ptr(), rightLen);
    }
 
-   mDirManager->Deref(splitBlock.f);
-
    // Copy remaining blocks to NEW block array and
    // swap the NEW block array in for the old
    for (i = b + 1; i < numBlocks; i++)
@@ -681,13 +663,10 @@ bool Sequence::InsertSilence(sampleCount s0, sampleCount len)
       silentFile = make_blockfile<SilentBlockFile>(idealSamples);
    while (len >= idealSamples) {
       sTrack.mBlock.push_back(SeqBlock(silentFile, pos));
-      mDirManager->Ref(silentFile);
 
       pos += idealSamples;
       len -= idealSamples;
    }
-   if (silentFile)
-      mDirManager->Deref(silentFile);
    if (len) {
       sTrack.mBlock.push_back(SeqBlock(
          make_blockfile<SilentBlockFile>(len), pos));
@@ -1151,11 +1130,8 @@ bool Sequence::CopyWrite(SampleBuffer &scratch,
    Read(scratch.ptr(), mSampleFormat, b, 0, length);
    memcpy(scratch.ptr() + start*sampleSize, buffer, len*sampleSize);
 
-   BlockFile *const oldBlockFile = b.f;
    b.f = mDirManager->NewSimpleBlockFile(scratch.ptr(), length, mSampleFormat);
 
-   mDirManager->Deref(oldBlockFile);
-
    return true;
 }
 
@@ -1233,7 +1209,6 @@ bool Sequence::Set(samplePtr buffer, sampleFormat format,
          if (start == block.start &&
              blen == fileLength) {
 
-            mDirManager->Deref(block.f);
             block.f = make_blockfile<SilentBlockFile>(blen);
          }
          else {
@@ -1545,7 +1520,6 @@ bool Sequence::Append(samplePtr buffer, sampleFormat format,
          static_cast< SimpleBlockFile * >( &*newLastBlock.f )
             ->SaveXML( *blockFileLog );
 
-      mDirManager->Deref(lastBlock.f);
       lastBlock = newLastBlock;
 
       len -= addLen;
@@ -1651,12 +1625,10 @@ bool Sequence::Delete(sampleCount start, sampleCount len)
       Read(scratch.ptr() + (pos * sampleSize), mSampleFormat,
            b, pos + len, newLen - pos);
 
-      BlockFile *const oldFile = b.f;
       b = SeqBlock(
          mDirManager->NewSimpleBlockFile(scratch.ptr(), newLen, mSampleFormat),
          b.start
       );
-      mDirManager->Deref(oldFile);
 
       for (unsigned int j = b0 + 1; j < numBlocks; j++)
          mBlock[j].start -= len;
@@ -1705,8 +1677,6 @@ bool Sequence::Delete(sampleCount start, sampleCount len)
 
          newBlock.erase(newBlock.end() - 1);
          Blockify(newBlock, prepreBlock.start, scratch.ptr(), sum);
-
-         mDirManager->Deref(prepreBlock.f);
       }
    }
    else {
@@ -1714,15 +1684,6 @@ bool Sequence::Delete(sampleCount start, sampleCount len)
       // right on the beginning of a block.
    }
 
-   if (b0 != b1) {
-      mDirManager->Deref(preBlock.f);
-   }
-
-   // Next, DELETE blocks strictly between b0 and b1
-   for (i = b0 + 1; i < b1; i++) {
-      mDirManager->Deref(mBlock[i].f);
-   }
-
    // Now, symmetrically, grab the samples in block b1 after the
    // deletion point into postBuffer.  If this is enough samples
    // for its own block, or if this would be the last block in
@@ -1757,15 +1718,12 @@ bool Sequence::Delete(sampleCount start, sampleCount len)
 
          Blockify(newBlock, start, scratch.ptr(), sum);
          b1++;
-
-         mDirManager->Deref(postpostBlock.f);
       }
    }
    else {
       // The sample where we begin deletion happens to fall
       // right on the end of a block.
    }
-   mDirManager->Deref(postBlock.f);
 
    // Copy the remaining blocks over from the old array
    for (i = b1 + 1; i < numBlocks; i++)
@@ -1822,11 +1780,11 @@ void Sequence::DebugPrintf(wxString *dest) const
    for (i = 0; i < mBlock.size(); i++) {
       const SeqBlock &seqBlock = mBlock[i];
       *dest += wxString::Format
-         (wxT("   Block %3u: start %8lld, len %8lld, refs %d, "),
+         (wxT("   Block %3u: start %8lld, len %8lld, refs %ld, "),
           i,
           (long long) seqBlock.start,
           seqBlock.f ? (long long) seqBlock.f->GetLength() : 0,
-          seqBlock.f ? mDirManager->GetRefCount(seqBlock.f) : 0);
+          seqBlock.f ? seqBlock.f.use_count() : 0);
 
       if (seqBlock.f)
          *dest += seqBlock.f->GetFileName().name.GetFullName();
diff --git a/src/Sequence.h b/src/Sequence.h
index a7630b527..fa051e8a6 100644
--- a/src/Sequence.h
+++ b/src/Sequence.h
@@ -30,7 +30,7 @@ typedef wxLongLong_t sampleCount; /** < A native 64-bit integer type, because
 #endif
 
 class BlockFile;
-using BlockFilePtr = BlockFile *;
+using BlockFilePtr = std::shared_ptr<BlockFile>;
 
 class DirManager;
 
@@ -238,8 +238,6 @@ class PROFILE_DLL_API Sequence final : public XMLTagHandler{
    // Private methods
    //
 
-   void DerefAllFiles();
-
    int FindBlock(sampleCount pos) const;
 
    bool AppendBlock(const SeqBlock &b);
diff --git a/src/blockfile/ODPCMAliasBlockFile.cpp b/src/blockfile/ODPCMAliasBlockFile.cpp
index f56e400e4..87cdb705d 100644
--- a/src/blockfile/ODPCMAliasBlockFile.cpp
+++ b/src/blockfile/ODPCMAliasBlockFile.cpp
@@ -74,33 +74,6 @@ ODPCMAliasBlockFile::~ODPCMAliasBlockFile()
 {
 }
 
-/// Increases the reference count of this block by one.  Only
-/// DirManager should call this method.
-/// This method has been overidden to be threadsafe.  It is important especially
-/// if two blockfiles deref at the same time resulting in a double deletion of the file
-void ODPCMAliasBlockFile::Ref() const
-{
-   mRefMutex.Lock();
-   BlockFile::Ref();
-   mRefMutex.Unlock();
-}
-
-/// Decreases the reference count of this block by one.  If this
-/// causes the count to become zero, deletes the associated disk
-/// file and deletes this object
-bool ODPCMAliasBlockFile::Deref() const
-{
-   bool ret;
-   mDerefMutex.Lock();
-   ret = BlockFile::Deref();
-   if(!ret)
-   {
-      //Deref returns true when deleted, in which case we should not be touching instance variables, or ever calling this function again.
-      mDerefMutex.Unlock();
-   }
-   return ret;
-}
-
 
 
 //Check to see if we have the file for these calls.
diff --git a/src/blockfile/ODPCMAliasBlockFile.h b/src/blockfile/ODPCMAliasBlockFile.h
index 8d8e3e7f7..adb9b88bd 100644
--- a/src/blockfile/ODPCMAliasBlockFile.h
+++ b/src/blockfile/ODPCMAliasBlockFile.h
@@ -143,13 +143,6 @@ protected:
       sampleFormat format, ArrayOf<char> &cleanup) override;
 
   private:
-   //Thread-safe versions
-   void Ref() const override;
-   bool Deref() const override;
-   //needed for Ref/Deref access.
-   friend class DirManager;
-   friend class ODComputeSummaryTask;
-   friend class ODDecodeTask;
 
    ODLock mWriteSummaryMutex;
 
@@ -162,11 +155,6 @@ protected:
    //lock the read data - libsndfile can't handle two reads at once?
    mutable ODLock mReadDataMutex;
 
-
-   //lock the Ref counting
-   mutable ODLock mDerefMutex;
-   mutable ODLock mRefMutex;
-
    mutable ODLock    mSummaryAvailableMutex;
    bool mSummaryAvailable;
    bool mSummaryBeingComputed;
diff --git a/src/ondemand/ODComputeSummaryTask.cpp b/src/ondemand/ODComputeSummaryTask.cpp
index 81c5533f0..f82e18b2e 100644
--- a/src/ondemand/ODComputeSummaryTask.cpp
+++ b/src/ondemand/ODComputeSummaryTask.cpp
@@ -49,8 +49,6 @@ void ODComputeSummaryTask::Terminate()
    //The terminate block won't allow DoSomeInternal and this method to be run async, so this is thread-safe.
    //Deref the block files since they are ref'ed when put into the array.
    mBlockFilesMutex.Lock();
-   for(unsigned int i=0;i<mBlockFiles.size();i++)
-      mBlockFiles[i]->Deref();
    mBlockFiles.clear();
    mBlockFilesMutex.Unlock();
 }
@@ -78,7 +76,7 @@ void ODComputeSummaryTask::DoSomeInternal()
       //first check to see if the ref count is at least 2.  It should have one
       //from when we added it to this instance's mBlockFiles array, and one from
       //the Wavetrack/sequence.  If it doesn't it has been deleted and we should forget it.
-      if(bf->RefCount()>=2)
+      if(bf.use_count() >= 2)
       {
          bf->DoWriteSummary();
          success = true;
@@ -93,8 +91,6 @@ void ODComputeSummaryTask::DoSomeInternal()
          mMaxBlockFiles--;
       }
 
-      //Release the refcount we placed on it.
-      bf->Deref();
       //take it out of the array - we are done with it.
       mBlockFiles.erase(mBlockFiles.begin());
 
@@ -169,7 +165,7 @@ void ODComputeSummaryTask::CalculatePercentComplete()
 ///by default left to right, or frome the point the user has clicked.
 void ODComputeSummaryTask::Update()
 {
-   std::vector<ODPCMAliasBlockFile*> tempBlocks;
+   std::vector< std::shared_ptr< ODPCMAliasBlockFile > > tempBlocks;
 
    mWaveTrackMutex.Lock();
 
@@ -204,8 +200,8 @@ void ODComputeSummaryTask::Update()
                const auto &file = block.f;
                if(file->IsDataAvailable() && !file->IsSummaryAvailable())
                {
-                  file->Ref();
-                  ODPCMAliasBlockFile *const odpcmaFile = static_cast<ODPCMAliasBlockFile*>(file);
+                  const auto odpcmaFile =
+                     std::static_pointer_cast<ODPCMAliasBlockFile>(file);
                   odpcmaFile->SetStart(block.start);
                   odpcmaFile->SetClipOffset((sampleCount)(clip->GetStartTime()*clip->GetRate()));
 
@@ -234,11 +230,9 @@ void ODComputeSummaryTask::Update()
 
 
 ///Computes the summary calculation queue order of the blockfiles
-void ODComputeSummaryTask::OrderBlockFiles(std::vector<ODPCMAliasBlockFile*> &unorderedBlocks)
+void ODComputeSummaryTask::OrderBlockFiles
+   (std::vector< std::shared_ptr< ODPCMAliasBlockFile > > &unorderedBlocks)
 {
-   //we are going to take things out of the array.  But first deref them since we ref them when we put them in.
-   for(unsigned int i=0;i<mBlockFiles.size();i++)
-      mBlockFiles[i]->Deref();
    mBlockFiles.clear();
    //Order the blockfiles into our queue in a fancy convenient way.  (this could be user-prefs)
    //for now just put them in linear.  We start the order from the first block that includes the ondemand sample
@@ -252,7 +246,7 @@ void ODComputeSummaryTask::OrderBlockFiles(std::vector<ODPCMAliasBlockFile*> &un
       //check to see if the refcount is at least two before we add it to the list.
       //There should be one Ref() from the one added by this ODTask, and one from the track.
       //If there isn't, then the block was deleted for some reason and we should ignore it.
-      if(unorderedBlocks[i]->RefCount()>=2)
+      if(unorderedBlocks[i].use_count() >= 2)
       {
          //test if the blockfiles are near the task cursor.  we use the last mBlockFiles[0] as our point of reference
          //and add ones that are closer.
@@ -276,7 +270,6 @@ void ODComputeSummaryTask::OrderBlockFiles(std::vector<ODPCMAliasBlockFile*> &un
       else
       {
          //Otherwise, let it be deleted and forget about it.
-         unorderedBlocks[i]->Deref();
       }
    }
 }
diff --git a/src/ondemand/ODComputeSummaryTask.h b/src/ondemand/ODComputeSummaryTask.h
index 374122d47..2863e4214 100644
--- a/src/ondemand/ODComputeSummaryTask.h
+++ b/src/ondemand/ODComputeSummaryTask.h
@@ -64,7 +64,8 @@ protected:
    void Update() override;
 
    ///Orders the input as either On-Demand or default layered order.
-   void OrderBlockFiles(std::vector<ODPCMAliasBlockFile*> &unorderedBlocks);
+   void OrderBlockFiles
+      (std::vector< std::shared_ptr< ODPCMAliasBlockFile > > &unorderedBlocks);
 
    ///tells us whether or not Update has been run at least once.
    void MarkUpdateRan();
@@ -72,7 +73,7 @@ protected:
 
    //mBlockFiles is touched on several threads- the OD terminate thread, and the task thread, so we need to mutex it.
    ODLock  mBlockFilesMutex;
-   std::vector<ODPCMAliasBlockFile*> mBlockFiles;
+   std::vector< std::shared_ptr< ODPCMAliasBlockFile > > mBlockFiles;
    int mMaxBlockFiles;
    int mComputedBlockFiles;
    ODLock  mHasUpdateRanMutex;
diff --git a/src/ondemand/ODDecodeTask.cpp b/src/ondemand/ODDecodeTask.cpp
index 30c0c27e2..cffd84a36 100644
--- a/src/ondemand/ODDecodeTask.cpp
+++ b/src/ondemand/ODDecodeTask.cpp
@@ -56,7 +56,7 @@ void ODDecodeTask::DoSomeInternal()
       //first check to see if the ref count is at least 2.  It should have one
       //from when we added it to this instance's mBlockFiles array, and one from
       //the Wavetrack/sequence.  If it doesn't it has been deleted and we should forget it.
-      if(bf->RefCount()>=2)
+      if(bf.use_count()>=2)
       {
          //OD TODO: somehow pass the bf a reference to the decoder that manages it's file.
          //we need to ensure that the filename won't change or be moved.  We do this by calling LockRead(),
@@ -86,7 +86,6 @@ void ODDecodeTask::DoSomeInternal()
 
       //Release the refcount we placed on it if we are successful
       if(ret >= 0 ) {
-         bf->Deref();
          //take it out of the array - we are done with it.
          mBlockFiles.erase(mBlockFiles.begin());
 
@@ -126,8 +125,7 @@ bool ODDecodeTask::SeekingAllowed()
 ///by default creates the order of the wavetrack to load.
 void ODDecodeTask::Update()
 {
-
-   std::vector<ODDecodeBlockFile*> tempBlocks;
+   std::vector< std::shared_ptr< ODDecodeBlockFile > > tempBlocks;
 
    mWaveTrackMutex.Lock();
 
@@ -154,12 +152,12 @@ void ODDecodeTask::Update()
             {
                //since we have more than one ODBlockFile, we will need type flags to cast.
                SeqBlock &block = (*blocks)[i];
-               BlockFile *const file = block.f;
-               ODDecodeBlockFile *oddbFile;
+               const auto &file = block.f;
+               std::shared_ptr<ODDecodeBlockFile> oddbFile;
                if (!file->IsDataAvailable() &&
-                   (oddbFile = static_cast<ODDecodeBlockFile*>(file))->GetDecodeType() == this->GetODType())
+                   (oddbFile =
+                       std::static_pointer_cast<ODDecodeBlockFile>(file))->GetDecodeType() == this->GetODType())
                {
-                  file->Ref();
                   oddbFile->SetStart(block.start);
                   oddbFile->SetClipOffset((sampleCount)(clip->GetStartTime()*clip->GetRate()));
 
@@ -186,11 +184,9 @@ void ODDecodeTask::Update()
 
 
 ///Orders the input as either On-Demand or default layered order.
-void ODDecodeTask::OrderBlockFiles(std::vector<ODDecodeBlockFile*> &unorderedBlocks)
+void ODDecodeTask::OrderBlockFiles
+   (std::vector< std::shared_ptr< ODDecodeBlockFile > > &unorderedBlocks)
 {
-   //we are going to take things out of the array.  But first deref them since we ref them when we put them in.
-   for(unsigned int i=0;i<mBlockFiles.size();i++)
-      mBlockFiles[i]->Deref();
    mBlockFiles.clear();
    //TODO:order the blockfiles into our queue in a fancy convenient way.  (this could be user-prefs)
    //for now just put them in linear.  We start the order from the first block that includes the ondemand sample
@@ -203,7 +199,7 @@ void ODDecodeTask::OrderBlockFiles(std::vector<ODDecodeBlockFile*> &unorderedBlo
       //check to see if the refcount is at least two before we add it to the list.
       //There should be one Ref() from the one added by this ODTask, and one from the track.
       //If there isn't, then the block was deleted for some reason and we should ignore it.
-      if(unorderedBlocks[i]->RefCount()>=2)
+      if(unorderedBlocks[i].use_count() >= 2)
       {
          //test if the blockfiles are near the task cursor.  we use the last mBlockFiles[0] as our point of reference
          //and add ones that are closer.
@@ -227,8 +223,6 @@ void ODDecodeTask::OrderBlockFiles(std::vector<ODDecodeBlockFile*> &unorderedBlo
       }
       else
       {
-         //Otherwise, let it be deleted and forget about it.
-         unorderedBlocks[i]->Deref();
       }
    }
 
diff --git a/src/ondemand/ODDecodeTask.h b/src/ondemand/ODDecodeTask.h
index 85fe4deaf..59eb27ec6 100644
--- a/src/ondemand/ODDecodeTask.h
+++ b/src/ondemand/ODDecodeTask.h
@@ -85,10 +85,11 @@ protected:
    void Update() override;
 
    ///Orders the input as either On-Demand or default layered order.
-   void OrderBlockFiles(std::vector<ODDecodeBlockFile*> &unorderedBlocks);
+   void OrderBlockFiles
+      (std::vector< std::shared_ptr< ODDecodeBlockFile > > &unorderedBlocks);
 
 
-   std::vector<ODDecodeBlockFile*> mBlockFiles;
+   std::vector<std::shared_ptr<ODDecodeBlockFile>> mBlockFiles;
    std::vector<movable_ptr<ODFileDecoder>> mDecoders;
 
    int mMaxBlockFiles;