diff --git a/src/LabelTrack.cpp b/src/LabelTrack.cpp
index f08eb48dd..78ad375e6 100644
--- a/src/LabelTrack.cpp
+++ b/src/LabelTrack.cpp
@@ -1133,7 +1133,7 @@ double LabelTrack::GetEndTime() const
    return end;
 }
 
-Track *LabelTrack::Duplicate()
+Track *LabelTrack::Duplicate() const
 {
    return new LabelTrack(*this);
 }
diff --git a/src/LabelTrack.h b/src/LabelTrack.h
index 23ecb4655..849e0d1fc 100644
--- a/src/LabelTrack.h
+++ b/src/LabelTrack.h
@@ -139,7 +139,7 @@ class AUDACITY_DLL_API LabelTrack : public Track
    virtual double GetStartTime() const;
    virtual double GetEndTime() const;
 
-   virtual Track *Duplicate();
+   virtual Track *Duplicate() const;
 
    virtual void SetSelected(bool s);
 
diff --git a/src/NoteTrack.cpp b/src/NoteTrack.cpp
index 44fcaec8f..be970063f 100644
--- a/src/NoteTrack.cpp
+++ b/src/NoteTrack.cpp
@@ -135,7 +135,7 @@ NoteTrack::~NoteTrack()
    }
 }
 
-Track *NoteTrack::Duplicate()
+Track *NoteTrack::Duplicate() const
 {
    NoteTrack *duplicate = new NoteTrack(mDirManager);
    duplicate->Init(*this);
diff --git a/src/NoteTrack.h b/src/NoteTrack.h
index d77c74d08..1e890ff78 100644
--- a/src/NoteTrack.h
+++ b/src/NoteTrack.h
@@ -57,7 +57,7 @@ class AUDACITY_DLL_API NoteTrack:public Track {
    NoteTrack(DirManager * projDirManager);
    virtual ~NoteTrack();
 
-   virtual Track *Duplicate();
+   virtual Track *Duplicate() const;
 
    virtual int GetKind() const { return Note; }
 
diff --git a/src/Tags.cpp b/src/Tags.cpp
index 4bd735f98..372c51769 100644
--- a/src/Tags.cpp
+++ b/src/Tags.cpp
@@ -371,27 +371,33 @@ int Tags::GetGenre(const wxString & name)
    return 255;
 }
 
-bool Tags::HasTag(const wxString & name)
+bool Tags::HasTag(const wxString & name) const
 {
    wxString key = name;
    key.UpperCase();
 
-   TagMap::iterator iter = mXref.find(key);
+   auto iter = mXref.find(key);
    return (iter != mXref.end());
 }
 
-wxString Tags::GetTag(const wxString & name)
+wxString Tags::GetTag(const wxString & name) const
 {
    wxString key = name;
    key.UpperCase();
 
-   TagMap::iterator iter = mXref.find(key);
+   auto iter = mXref.find(key);
 
    if (iter == mXref.end()) {
       return wxEmptyString;
    }
 
-   return mMap[iter->second];
+   auto iter2 = mMap.find(iter->second);
+   if (iter2 == mMap.end()) {
+      wxASSERT(false);
+      return wxEmptyString;
+   }
+   else
+      return iter2->second;
 }
 
 Tags::Iterators Tags::GetRange() const
diff --git a/src/Tags.h b/src/Tags.h
index 9373c54ec..bb7521702 100644
--- a/src/Tags.h
+++ b/src/Tags.h
@@ -97,8 +97,8 @@ class AUDACITY_DLL_API Tags: public XMLTagHandler {
    wxString GetGenre(int value);
    int GetGenre(const wxString & name);
 
-   bool HasTag(const wxString & name);
-   wxString GetTag(const wxString & name);
+   bool HasTag(const wxString & name) const;
+   wxString GetTag(const wxString & name) const;
 
    using IterPair = std::pair<TagMap::const_iterator, TagMap::const_iterator>;
    struct Iterators : public IterPair {
diff --git a/src/TimeTrack.cpp b/src/TimeTrack.cpp
index 6d20fe7b8..ab8bb1b8c 100644
--- a/src/TimeTrack.cpp
+++ b/src/TimeTrack.cpp
@@ -64,7 +64,7 @@ TimeTrack::TimeTrack(DirManager *projDirManager, const ZoomInfo *zoomInfo):
    blankPen.SetColour(214, 214, 214);
 }
 
-TimeTrack::TimeTrack(TimeTrack &orig):
+TimeTrack::TimeTrack(const TimeTrack &orig):
    Track(orig)
    , mZoomInfo(orig.mZoomInfo)
 {
@@ -109,7 +109,7 @@ TimeTrack::~TimeTrack()
    delete mRuler;
 }
 
-Track *TimeTrack::Duplicate()
+Track *TimeTrack::Duplicate() const
 {
    return new TimeTrack(*this);
 }
diff --git a/src/TimeTrack.h b/src/TimeTrack.h
index c148fb503..89747936b 100644
--- a/src/TimeTrack.h
+++ b/src/TimeTrack.h
@@ -35,7 +35,7 @@ class TimeTrack: public Track {
     * copy-constructor to encapsulate this.
     * @param orig The original track to copy from
     */
-   TimeTrack(TimeTrack &orig);
+   TimeTrack(const TimeTrack &orig);
 
    virtual ~TimeTrack();
 
@@ -131,7 +131,7 @@ class TimeTrack: public Track {
     * @param orig the TimeTrack to copy from
     */
    void Init(const TimeTrack &orig);
-   virtual Track *Duplicate();
+   virtual Track *Duplicate() const;
 
    friend class TrackFactory;
 
diff --git a/src/Track.h b/src/Track.h
index a2540da00..9950fbbad 100644
--- a/src/Track.h
+++ b/src/Track.h
@@ -145,7 +145,7 @@ class AUDACITY_DLL_API Track: public XMLTagHandler
    virtual ~ Track();
 
    void Init(const Track &orig);
-   virtual Track *Duplicate() = 0;
+   virtual Track *Duplicate() const = 0;
 
    // Called when this track is merged to stereo with another, and should
    // take on some paramaters of its partner.
@@ -239,6 +239,30 @@ class AUDACITY_DLL_API TrackListIterator
    TrackListNode *cur;
 };
 
+class AUDACITY_DLL_API TrackListConstIterator
+{
+public:
+   TrackListConstIterator(const TrackList * val = NULL)
+      : mIter(const_cast<TrackList*>(val))
+   {}
+   ~TrackListConstIterator() {}
+
+   // Iterate functions
+   const Track *First(const TrackList * val = NULL)
+   { return mIter.First(const_cast<TrackList*>(val)); }
+   const Track *StartWith(const Track * val)
+   { return mIter.StartWith(const_cast<Track*>(val)); }
+   const Track *Next(bool skiplinked = false)
+   { return mIter.Next(skiplinked); }
+   const Track *Prev(bool skiplinked = false)
+   { return mIter.Prev(skiplinked); }
+   const Track *Last(bool skiplinked = false)
+   { return mIter.Last(skiplinked); }
+
+private:
+   TrackListIterator mIter;
+};
+
 // TrackListCondIterator (base class for iterators that iterate over all tracks)
 // that meet a condition)
 class AUDACITY_DLL_API TrackListCondIterator: public TrackListIterator
diff --git a/src/UndoManager.cpp b/src/UndoManager.cpp
index 68c8726f1..2255949f7 100644
--- a/src/UndoManager.cpp
+++ b/src/UndoManager.cpp
@@ -182,7 +182,7 @@ bool UndoManager::RedoAvailable()
    return (current < (int)stack.size() - 1);
 }
 
-void UndoManager::ModifyState(TrackList * l,
+void UndoManager::ModifyState(const TrackList * l,
                               const SelectedRegion &selectedRegion)
 {
    if (current == wxNOT_FOUND) {
@@ -195,8 +195,8 @@ void UndoManager::ModifyState(TrackList * l,
 
    // Duplicate
    auto tracksCopy = std::make_unique<TrackList>(true);
-   TrackListIterator iter(l);
-   Track *t = iter.First();
+   TrackListConstIterator iter(l);
+   const Track *t = iter.First();
    while (t) {
       tracksCopy->Add(t->Duplicate());
       t = iter.Next();
@@ -208,7 +208,7 @@ void UndoManager::ModifyState(TrackList * l,
    SonifyEndModifyState();
 }
 
-void UndoManager::PushState(TrackList * l,
+void UndoManager::PushState(const TrackList * l,
                             const SelectedRegion &selectedRegion,
                             const wxString &longDescription,
                             const wxString &shortDescription,
@@ -237,8 +237,8 @@ void UndoManager::PushState(TrackList * l,
    }
 
    auto tracksCopy = std::make_unique<TrackList>(true);
-   TrackListIterator iter(l);
-   Track *t = iter.First();
+   TrackListConstIterator iter(l);
+   const Track *t = iter.First();
    while (t) {
       tracksCopy->Add(t->Duplicate());
       t = iter.Next();
diff --git a/src/UndoManager.h b/src/UndoManager.h
index 6cc6c1b8f..6073e1888 100644
--- a/src/UndoManager.h
+++ b/src/UndoManager.h
@@ -99,11 +99,11 @@ class AUDACITY_DLL_API UndoManager {
    UndoManager();
    ~UndoManager();
 
-   void PushState(TrackList * l,
+   void PushState(const TrackList * l,
                   const SelectedRegion &selectedRegion,
                   const wxString &longDescription, const wxString &shortDescription,
                   UndoPush flags = UndoPush::AUTOSAVE);
-   void ModifyState(TrackList * l,
+   void ModifyState(const TrackList * l,
                     const SelectedRegion &selectedRegion);
    void ClearStates();
    void RemoveStates(int num);  // removes the 'num' oldest states
diff --git a/src/WaveTrack.cpp b/src/WaveTrack.cpp
index 0a78fd175..bc07c2e94 100644
--- a/src/WaveTrack.cpp
+++ b/src/WaveTrack.cpp
@@ -116,7 +116,7 @@ WaveTrack::WaveTrack(DirManager *projDirManager, sampleFormat format, double rat
    mAutoSaveIdent = 0;
 }
 
-WaveTrack::WaveTrack(WaveTrack &orig):
+WaveTrack::WaveTrack(const WaveTrack &orig):
    Track(orig)
    , mpSpectrumSettings(orig.mpSpectrumSettings
         ? new SpectrogramSettings(*orig.mpSpectrumSettings) : 0
@@ -362,7 +362,7 @@ void WaveTrack::SetSpectrumBounds(float min, float max)
    mSpectrumMax = max;
 }
 
-Track *WaveTrack::Duplicate()
+Track *WaveTrack::Duplicate() const
 {
    return new WaveTrack(*this);
 }
diff --git a/src/WaveTrack.h b/src/WaveTrack.h
index 0c6476e30..957efd1aa 100644
--- a/src/WaveTrack.h
+++ b/src/WaveTrack.h
@@ -72,10 +72,10 @@ class AUDACITY_DLL_API WaveTrack : public Track {
    WaveTrack(DirManager * projDirManager,
              sampleFormat format = (sampleFormat)0,
              double rate = 0);
-   WaveTrack(WaveTrack &orig);
+   WaveTrack(const WaveTrack &orig);
 
    void Init(const WaveTrack &orig);
-   virtual Track *Duplicate();
+   virtual Track *Duplicate() const;
 #ifdef EXPERIMENTAL_OUTPUT_DISPLAY
    void VirtualStereoInit();
 #endif
diff --git a/src/export/Export.h b/src/export/Export.h
index c3b6e2a5f..eb5e98ca9 100644
--- a/src/export/Export.h
+++ b/src/export/Export.h
@@ -110,7 +110,7 @@ public:
                        double t0,
                        double t1,
                        MixerSpec *mixerSpec = NULL,
-                       Tags *metadata = NULL,
+                       const Tags *metadata = NULL,
                        int subformat = 0) = 0;
 
 protected:
diff --git a/src/export/ExportCL.cpp b/src/export/ExportCL.cpp
index fe85c6a3e..a8fec1bd0 100644
--- a/src/export/ExportCL.cpp
+++ b/src/export/ExportCL.cpp
@@ -291,7 +291,7 @@ public:
                double t0,
                double t1,
                MixerSpec *mixerSpec = NULL,
-               Tags *metadata = NULL,
+               const Tags *metadata = NULL,
                int subformat = 0) override;
 };
 
@@ -318,7 +318,7 @@ int ExportCL::Export(AudacityProject *project,
                       double t0,
                       double t1,
                       MixerSpec *mixerSpec,
-                      Tags *WXUNUSED(metadata),
+                      const Tags *WXUNUSED(metadata),
                       int WXUNUSED(subformat))
 {
    wxString output;
diff --git a/src/export/ExportFFmpeg.cpp b/src/export/ExportFFmpeg.cpp
index 886aeb62e..b74a77f13 100644
--- a/src/export/ExportFFmpeg.cpp
+++ b/src/export/ExportFFmpeg.cpp
@@ -101,16 +101,16 @@ public:
    bool CheckFileName(wxFileName &filename, int format = 0);
 
    /// Format intialization
-   bool Init(const char *shortname, AudacityProject *project, Tags *metadata, int subformat);
+   bool Init(const char *shortname, AudacityProject *project, const Tags *metadata, int subformat);
 
    /// Codec intialization
    bool InitCodecs(AudacityProject *project);
 
    /// Writes metadata
-   bool AddTags(Tags *metadata);
+   bool AddTags(const Tags *metadata);
 
    /// Sets individual metadata values
-   void SetMetadata(Tags *tags, const char *name, const wxChar *tag);
+   void SetMetadata(const Tags *tags, const char *name, const wxChar *tag);
 
    /// Encodes audio
    bool EncodeAudioFrame(int16_t *pFrame, int frameSize);
@@ -145,7 +145,7 @@ public:
       double t0,
       double t1,
       MixerSpec *mixerSpec = NULL,
-      Tags *metadata = NULL,
+      const Tags *metadata = NULL,
       int subformat = 0) override;
 
 private:
@@ -256,7 +256,7 @@ bool ExportFFmpeg::CheckFileName(wxFileName & WXUNUSED(filename), int WXUNUSED(f
    return result;
 }
 
-bool ExportFFmpeg::Init(const char *shortname, AudacityProject *project, Tags *metadata, int subformat)
+bool ExportFFmpeg::Init(const char *shortname, AudacityProject *project, const Tags *metadata, int subformat)
 {
    int err;
    //FFmpegLibsInst->LoadLibs(NULL,true); //Loaded at startup or from Prefs now
@@ -792,7 +792,7 @@ bool ExportFFmpeg::EncodeAudioFrame(int16_t *pFrame, int frameSize)
 
 int ExportFFmpeg::Export(AudacityProject *project,
                        int channels, const wxString &fName,
-                       bool selectionOnly, double t0, double t1, MixerSpec *mixerSpec, Tags *metadata, int subformat)
+                       bool selectionOnly, double t0, double t1, MixerSpec *mixerSpec, const Tags *metadata, int subformat)
 {
    if (!CheckFFmpegPresence())
       return false;
@@ -873,7 +873,7 @@ void AddStringTagANSI(char field[], int size, wxString value)
       memcpy(field,value.mb_str(),(int)strlen(value.mb_str()) > size -1 ? size -1 : strlen(value.mb_str()));
 }
 
-bool ExportFFmpeg::AddTags(Tags *tags)
+bool ExportFFmpeg::AddTags(const Tags *tags)
 {
    if (tags == NULL)
    {
@@ -891,7 +891,7 @@ bool ExportFFmpeg::AddTags(Tags *tags)
    return true;
 }
 
-void ExportFFmpeg::SetMetadata(Tags *tags, const char *name, const wxChar *tag)
+void ExportFFmpeg::SetMetadata(const Tags *tags, const char *name, const wxChar *tag)
 {
    if (tags->HasTag(tag))
    {
diff --git a/src/export/ExportFLAC.cpp b/src/export/ExportFLAC.cpp
index 3fa6a5a13..e25057443 100644
--- a/src/export/ExportFLAC.cpp
+++ b/src/export/ExportFLAC.cpp
@@ -190,12 +190,12 @@ public:
                double t0,
                double t1,
                MixerSpec *mixerSpec = NULL,
-               Tags *metadata = NULL,
+               const Tags *metadata = NULL,
                int subformat = 0) override;
 
 private:
 
-   bool GetMetadata(AudacityProject *project, Tags *tags);
+   bool GetMetadata(AudacityProject *project, const Tags *tags);
 
    FLAC__StreamMetadata *mMetadata;
 };
@@ -225,7 +225,7 @@ int ExportFLAC::Export(AudacityProject *project,
                         double t0,
                         double t1,
                         MixerSpec *mixerSpec,
-                        Tags *metadata,
+                        const Tags *metadata,
                         int WXUNUSED(subformat))
 {
    double    rate    = project->GetRate();
@@ -380,7 +380,7 @@ wxWindow *ExportFLAC::OptionsCreate(wxWindow *parent, int format)
 //      expects that array to be valid until the stream is initialized.
 //
 //      This has been fixed in 1.1.4.
-bool ExportFLAC::GetMetadata(AudacityProject *project, Tags *tags)
+bool ExportFLAC::GetMetadata(AudacityProject *project, const Tags *tags)
 {
    // Retrieve tags if needed
    if (tags == NULL)
diff --git a/src/export/ExportMP2.cpp b/src/export/ExportMP2.cpp
index b870225ae..345f14cc2 100644
--- a/src/export/ExportMP2.cpp
+++ b/src/export/ExportMP2.cpp
@@ -181,12 +181,12 @@ public:
                double t0,
                double t1,
                MixerSpec *mixerSpec = NULL,
-               Tags *metadata = NULL,
+               const Tags *metadata = NULL,
                int subformat = 0) override;
 
 private:
 
-   int AddTags(AudacityProject *project, char **buffer, bool *endOfFile, Tags *tags);
+   int AddTags(AudacityProject *project, char **buffer, bool *endOfFile, const Tags *tags);
 #ifdef USE_LIBID3TAG
    void AddFrame(struct id3_tag *tp, const wxString & n, const wxString & v, const char *name);
 #endif
@@ -211,7 +211,7 @@ void ExportMP2::Destroy()
 
 int ExportMP2::Export(AudacityProject *project,
                int channels, const wxString &fName,
-               bool selectionOnly, double t0, double t1, MixerSpec *mixerSpec, Tags *metadata,
+               bool selectionOnly, double t0, double t1, MixerSpec *mixerSpec, const Tags *metadata,
                int WXUNUSED(subformat))
 {
    bool stereo = (channels == 2);
@@ -339,7 +339,7 @@ wxWindow *ExportMP2::OptionsCreate(wxWindow *parent, int format)
 }
 
 // returns buffer len; caller frees
-int ExportMP2::AddTags(AudacityProject * WXUNUSED(project), char **buffer, bool *endOfFile, Tags *tags)
+int ExportMP2::AddTags(AudacityProject * WXUNUSED(project), char **buffer, bool *endOfFile, const Tags *tags)
 {
 #ifdef USE_LIBID3TAG
    struct id3_tag *tp = id3_tag_new();
diff --git a/src/export/ExportMP3.cpp b/src/export/ExportMP3.cpp
index b2ac3c32b..4aad85f83 100644
--- a/src/export/ExportMP3.cpp
+++ b/src/export/ExportMP3.cpp
@@ -1569,7 +1569,7 @@ public:
                double t0,
                double t1,
                MixerSpec *mixerSpec = NULL,
-               Tags *metadata = NULL,
+               const Tags *metadata = NULL,
                int subformat = 0) override;
 
 private:
@@ -1577,7 +1577,7 @@ private:
    int FindValue(CHOICES *choices, int cnt, int needle, int def);
    wxString FindName(CHOICES *choices, int cnt, int needle);
    int AskResample(int bitrate, int rate, int lowrate, int highrate);
-   int AddTags(AudacityProject *project, char **buffer, bool *endOfFile, Tags *tags);
+   int AddTags(AudacityProject *project, char **buffer, bool *endOfFile, const Tags *tags);
 #ifdef USE_LIBID3TAG
    void AddFrame(struct id3_tag *tp, const wxString & n, const wxString & v, const char *name);
 #endif
@@ -1624,7 +1624,7 @@ int ExportMP3::Export(AudacityProject *project,
                        double t0,
                        double t1,
                        MixerSpec *mixerSpec,
-                       Tags *metadata,
+                       const Tags *metadata,
                        int WXUNUSED(subformat))
 {
    int rate = lrint(project->GetRate());
@@ -1965,7 +1965,7 @@ int ExportMP3::AskResample(int bitrate, int rate, int lowrate, int highrate)
 }
 
 // returns buffer len; caller frees
-int ExportMP3::AddTags(AudacityProject *WXUNUSED(project), char **buffer, bool *endOfFile, Tags *tags)
+int ExportMP3::AddTags(AudacityProject *WXUNUSED(project), char **buffer, bool *endOfFile, const Tags *tags)
 {
 #ifdef USE_LIBID3TAG
    struct id3_tag *tp = id3_tag_new();
diff --git a/src/export/ExportMultiple.cpp b/src/export/ExportMultiple.cpp
index 5d0382eab..7bf7897d2 100644
--- a/src/export/ExportMultiple.cpp
+++ b/src/export/ExportMultiple.cpp
@@ -911,7 +911,7 @@ int ExportMultiple::DoExport(int channels,
                               bool selectedOnly,
                               double t0,
                               double t1,
-                              Tags tags)
+                              const Tags &tags)
 {
    wxLogDebug(wxT("Doing multiple Export: File name \"%s\""), (name.GetFullName()).c_str());
    wxLogDebug(wxT("Channels: %i, Start: %lf, End: %lf "), channels, t0, t1);
diff --git a/src/export/ExportMultiple.h b/src/export/ExportMultiple.h
index 6771a6922..3e3b8bd8b 100644
--- a/src/export/ExportMultiple.h
+++ b/src/export/ExportMultiple.h
@@ -79,7 +79,7 @@ private:
                  bool selectedOnly,
                  double t0,
                  double t1,
-                 Tags tags);
+                 const Tags &tags);
    /** \brief Takes an arbitrary text string and converts it to a form that can
     * be used as a file name, if necessary prompting the user to edit the file
     * name produced */
diff --git a/src/export/ExportOGG.cpp b/src/export/ExportOGG.cpp
index b7f3c885f..f4300b802 100644
--- a/src/export/ExportOGG.cpp
+++ b/src/export/ExportOGG.cpp
@@ -140,12 +140,12 @@ public:
                double t0,
                double t1,
                MixerSpec *mixerSpec = NULL,
-               Tags *metadata = NULL,
+               const Tags *metadata = NULL,
                int subformat = 0) override;
 
 private:
 
-   bool FillComment(AudacityProject *project, vorbis_comment *comment, Tags *metadata);
+   bool FillComment(AudacityProject *project, vorbis_comment *comment, const Tags *metadata);
 };
 
 ExportOGG::ExportOGG()
@@ -171,7 +171,7 @@ int ExportOGG::Export(AudacityProject *project,
                        double t0,
                        double t1,
                        MixerSpec *mixerSpec,
-                       Tags *metadata,
+                       const Tags *metadata,
                        int WXUNUSED(subformat))
 {
    double    rate    = project->GetRate();
@@ -341,7 +341,7 @@ wxWindow *ExportOGG::OptionsCreate(wxWindow *parent, int format)
    return safenew ExportOGGOptions(parent, format);
 }
 
-bool ExportOGG::FillComment(AudacityProject *project, vorbis_comment *comment, Tags *metadata)
+bool ExportOGG::FillComment(AudacityProject *project, vorbis_comment *comment, const Tags *metadata)
 {
    // Retrieve tags from project if not over-ridden
    if (metadata == NULL)
diff --git a/src/export/ExportPCM.cpp b/src/export/ExportPCM.cpp
index 4c57fdfe5..86c822c65 100644
--- a/src/export/ExportPCM.cpp
+++ b/src/export/ExportPCM.cpp
@@ -320,7 +320,7 @@ public:
                double t0,
                double t1,
                MixerSpec *mixerSpec = NULL,
-               Tags *metadata = NULL,
+               const Tags *metadata = NULL,
                int subformat = 0) override;
    // optional
    wxString GetExtension(int index);
@@ -329,8 +329,8 @@ public:
 private:
 
    char *AdjustString(const wxString & wxStr, int sf_format);
-   bool AddStrings(AudacityProject *project, SNDFILE *sf, Tags *tags, int sf_format);
-   void AddID3Chunk(wxString fName, Tags *tags, int sf_format);
+   bool AddStrings(AudacityProject *project, SNDFILE *sf, const Tags *tags, int sf_format);
+   void AddID3Chunk(wxString fName, const Tags *tags, int sf_format);
 
 };
 
@@ -395,7 +395,7 @@ int ExportPCM::Export(AudacityProject *project,
                        double t0,
                        double t1,
                        MixerSpec *mixerSpec,
-                       Tags *metadata,
+                       const Tags *metadata,
                        int subformat)
 {
    double       rate = project->GetRate();
@@ -664,7 +664,7 @@ char *ExportPCM::AdjustString(const wxString & wxStr, int sf_format)
    return pDest;
 }
 
-bool ExportPCM::AddStrings(AudacityProject * WXUNUSED(project), SNDFILE *sf, Tags *tags, int sf_format)
+bool ExportPCM::AddStrings(AudacityProject * WXUNUSED(project), SNDFILE *sf, const Tags *tags, int sf_format)
 {
    if (tags->HasTag(TAG_TITLE)) {
       char * ascii7Str = AdjustString(tags->GetTag(TAG_TITLE), sf_format);
@@ -741,7 +741,7 @@ bool ExportPCM::AddStrings(AudacityProject * WXUNUSED(project), SNDFILE *sf, Tag
    return true;
 }
 
-void ExportPCM::AddID3Chunk(wxString fName, Tags *tags, int sf_format)
+void ExportPCM::AddID3Chunk(wxString fName, const Tags *tags, int sf_format)
 {
 #ifdef USE_LIBID3TAG
    struct id3_tag *tp = id3_tag_new();