ExportCL.cpp

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/**********************************************************************
 
  Audacity: A Digital Audio Editor
 
  ExportCL.cpp
 
  Joshua Haberman
 
  This code allows Audacity to export data by piping it to an external
  program.
 
**********************************************************************/
 
#include "ProjectRate.h"
 
#include <thread>
 
#include <wx/app.h>
#include <wx/cmdline.h>
#include <wx/combobox.h>
#include <wx/button.h>
#include <wx/log.h>
#include <wx/process.h>
#include <wx/sizer.h>
#include <wx/textctrl.h>
#if defined(__WXMSW__)
#include <wx/msw/registry.h> // for wxRegKey
#endif
 
#include "FileNames.h"
#include "Export.h"
 
#include "Mix.h"
#include "Prefs.h"
#include "SelectFile.h"
#include "ShuttleGui.h"
#include "Tags.h"
#include "Track.h"
#include "float_cast.h"
#include "widgets/FileHistory.h"
#include "wxPanelWrapper.h"
#include "widgets/Warning.h"
#include "wxFileNameWrapper.h"
#include "BasicUI.h"
 
#include "ExportOptionsEditor.h"
#include "ExportOptionsUIServices.h"
#include "ExportPluginHelpers.h"
#include "ExportPluginRegistry.h"
 
#ifdef USE_LIBID3TAG
   #include <id3tag.h>
   extern "C" {
      struct id3_frame *id3_frame_new(char const *);
   }
#endif
 
namespace
{
 
void Drain(wxInputStream *s, wxString *o)
{
   while (s->CanRead()) {
      char buffer[4096];
 
      s->Read(buffer, WXSIZEOF(buffer) - 1);
      buffer[s->LastRead()] = wxT('\0');
      *o += LAT1CTOWX(buffer);
   }
}
 
struct ExtendPath
{
#if defined(__WXMSW__)
   wxString opath;
 
   ExtendPath()
   {
      // Give Windows a chance at finding lame command in the default location.
      wxString paths[] = {wxT("HKEY_LOCAL_MACHINE\\Software\\Lame for Audacity"),
                          wxT("HKEY_LOCAL_MACHINE\\Software\\FFmpeg for Audacity")};
      wxString npath;
      wxRegKey reg;
 
      wxGetEnv(wxT("PATH"), &opath);
      npath = opath;
 
      for (int i = 0; i < WXSIZEOF(paths); i++) {
         reg.SetName(paths[i]);
 
         if (reg.Exists()) {
            wxString ipath;
            reg.QueryValue(wxT("InstallPath"), ipath);
            if (!ipath.empty()) {
               npath += wxPATH_SEP + ipath;
            }
         }
      }
 
      wxSetEnv(wxT("PATH"),npath);
   };
 
   ~ExtendPath()
   {
      if (!opath.empty())
      {
         wxSetEnv(wxT("PATH"),opath);
      }
   }
#endif
};
 
//----------------------------------------------------------------------------
// ExportCLProcess
//----------------------------------------------------------------------------
 
class ExportCLProcess final : public wxProcess
{
public:
   ExportCLProcess(wxString *output)
   {
#if defined(__WXMAC__)
      // Don't want to crash on broken pipe
      signal(SIGPIPE, SIG_IGN);
#endif
 
      mOutput = output;
      mActive = true;
      mStatus = -555;
      Redirect();
   }
 
   bool IsActive() const
   {
      return mActive;
   }
 
   void OnTerminate(int WXUNUSED( pid ), int status) override
   {
      Drain(GetInputStream(), mOutput);
      Drain(GetErrorStream(), mOutput);
 
      mStatus = status;
      mActive = false;
   }
 
   int GetStatus() const
   {
      return mStatus;
   }
 
private:
   wxString *mOutput;
   bool mActive;
   int mStatus;
};
 
}
 
enum : int {
   CLOptionIDCommand = 0,
   CLOptionIDShowOutput
};
 
const std::vector<ExportOption> CLOptions {
   { CLOptionIDCommand, {}, std::string() },
   { CLOptionIDShowOutput, {}, false }
};
 
class ExportOptionsCLEditor final
   : public ExportOptionsEditor
   , public ExportOptionsUIServices
{
   wxString mCommand {wxT("lame - \"%f\"")};
   bool mShowOutput {false};
   bool mInitialized {false};
public:
 
   ExportOptionsCLEditor() = default;
 
   void PopulateUI(ShuttleGui& S) override
   {
      if(!mInitialized)
      {
         mHistory.Load(*gPrefs, wxT("/FileFormats/ExternalProgramHistory"));
 
         if (mHistory.empty()) {
            mHistory.Append(wxT("ffmpeg -i - \"%f.opus\""));
            mHistory.Append(wxT("ffmpeg -i - \"%f.wav\""));
            mHistory.Append(wxT("ffmpeg -i - \"%f\""));
            mHistory.Append(wxT("lame - \"%f\""));
         }
 
         if(!mCommand.empty())
            mHistory.Append(mCommand);
 
         mInitialized = true;
      }
 
      mParent = wxGetTopLevelParent(S.GetParent());
 
      wxArrayStringEx cmds( mHistory.begin(), mHistory.end() );
      auto cmd = cmds[0];
 
      S.StartVerticalLay();
      {
         S.StartHorizontalLay(wxEXPAND);
         {
            S.SetSizerProportion(1);
            S.StartMultiColumn(3, wxEXPAND);
            {
               S.SetStretchyCol(1);
               mCommandBox = S.AddCombo(XXO("Command:"),
                                 cmd,
                                 cmds);
               mCommandBox->Bind(wxEVT_TEXT, [this](wxCommandEvent& event) {
                  mLastCommand = event.GetString();
               });
               mLastCommand = mCommandBox->GetValue();
               mCommandBox->SetMaxSize(wxSize(50,400));
 
               S.AddButton(XXO("Browse..."), wxALIGN_CENTER_VERTICAL)
                  ->Bind(wxEVT_BUTTON, &ExportOptionsCLEditor::OnBrowse, this);
 
               S.AddFixedText( {} );
               S.TieCheckBox(XXO("Show output"), mShowOutput);
            }
            S.EndMultiColumn();
         }
         S.EndHorizontalLay();
 
         S.AddTitle(XO(
   /* i18n-hint: Some programmer-oriented terminology here:
      "Data" refers to the sound to be exported, "piped" means sent,
      and "standard in" means the default input stream that the external program,
      named by %f, will read.  And yes, it's %f, not %s -- this isn't actually used
      in the program as a format string.  Keep %f unchanged. */
   "Data will be piped to standard in. \"%f\" uses the file name in the export window."), 250);
      }
      S.EndVerticalLay();
   }
 
   static bool IsValidCommand(const wxString& command)
   {
      wxArrayString argv = wxCmdLineParser::ConvertStringToArgs(command,
#if defined(__WXMSW__)
         wxCMD_LINE_SPLIT_DOS
#else
         wxCMD_LINE_SPLIT_UNIX
#endif
      );
 
      if (argv.empty()) {
         ShowExportErrorDialog(
            XO("Warning"),
            XO("Program name appears to be missing."),//":745"
            true);
         return false;
      }
 
      // Normalize the path (makes absolute and resolves variables)
      wxFileName cmd(argv[0]);
      cmd.Normalize(wxPATH_NORM_ALL & ~wxPATH_NORM_ABSOLUTE);
 
      // Just verify the given path exists if it is absolute.
      if (cmd.IsAbsolute()) {
         if (!cmd.Exists()) {
            BasicUI::ShowMessageBox(XO("\"%s\" couldn't be found.").Format(cmd.GetFullPath()),
                                    BasicUI::MessageBoxOptions()
                                       .IconStyle(BasicUI::Icon::Warning)
                                       .Caption(XO("Warning")));
            return false;
         }
 
         return true;
      }
 
      // Search for the command in the PATH list
      wxPathList pathlist;
      pathlist.AddEnvList(wxT("PATH"));
      wxString path = pathlist.FindAbsoluteValidPath(argv[0]);
 
   #if defined(__WXMSW__)
      if (path.empty()) {
         path = pathlist.FindAbsoluteValidPath(argv[0] + wxT(".exe"));
      }
   #endif
 
      if (path.empty()) {
         BasicUI::ShowMessageBox(XO("Unable to locate \"%s\" in your path.").Format(cmd.GetFullPath()),
                                 BasicUI::MessageBoxOptions()
                                    .IconStyle(BasicUI::Icon::Warning)
                                    .Caption(XO("Warning")));
         return false;
      }
 
      return true;
   }
 
   bool TransferDataFromWindow() override
   {
      if(IsValidCommand(mLastCommand))
      {
         mCommand = mLastCommand;
         mHistory.Append(mCommand);
         mHistory.Save(*gPrefs);
         return true;
      }
      return false;
   }
 
   SampleRateList GetSampleRateList() const override
   {
      return {};
   }
 
   int GetOptionsCount() const override
   {
      return static_cast<int>(CLOptions.size());
   }
 
   bool GetOption(int index, ExportOption& option) const override
   {
      if(index >= 0 && index < static_cast<int>(CLOptions.size()))
      {
         option = CLOptions[index];
         return true;
      }
      return false;
   }
 
   bool GetValue(int id, ExportValue& value) const override
   {
      if(id == CLOptionIDCommand)
      {
         value = std::string(mCommand.ToUTF8());
         return true;
      }
      if(id == CLOptionIDShowOutput)
      {
         value = mShowOutput;
         return true;
      }
      return false;
   }
 
   bool SetValue(int id, const ExportValue& value) override
   {
      if(id == CLOptionIDCommand && std::holds_alternative<std::string>(value))
      {
         mCommand = wxString::FromUTF8(*std::get_if<std::string>(&value));
         return true;
      }
      if(id == CLOptionIDShowOutput && std::holds_alternative<bool>(value))
      {
         mShowOutput = *std::get_if<bool>(&value);
         return true;
      }
      return false;
   }
 
   void Load(const audacity::BasicSettings& config) override
   {
      mCommand = config.Read(wxT("/FileFormats/ExternalProgramExportCommand"), mCommand);
      mShowOutput = config.Read(wxT("/FileFormats/ExternalProgramShowOutput"), mShowOutput);
   }
 
   void Store(audacity::BasicSettings& config) const override
   {
      config.Write(wxT("/FileFormats/ExternalProgramExportCommand"), mCommand);
      config.Write(wxT("/FileFormats/ExternalProgramShowOutput"), mShowOutput);
   }
 
private:
 
   void OnBrowse(const wxCommandEvent&)
   {
      wxString path;
      FileExtension ext;
      FileNames::FileType type = FileNames::AllFiles;
 
   #if defined(__WXMSW__)
      ext = wxT("exe");
      /* i18n-hint files that can be run as programs */
      type = { XO("Executables"), { ext } };
   #endif
 
      path = SelectFile(FileNames::Operation::Open,
         XO("Find path to command"),
         wxEmptyString,
         wxEmptyString,
         ext,
         { type },
         wxFD_OPEN | wxRESIZE_BORDER,
         mParent);
      if (path.empty()) {
         return;
      }
 
      if (path.Find(wxT(' ')) != wxNOT_FOUND)
         path = wxT('"') + path + wxT('"');
 
      mCommandBox->SetValue(path);
      mCommandBox->SetInsertionPointEnd();
   }
 
   wxWindow* mParent{nullptr};
   wxComboBox* mCommandBox{nullptr};
 
   //Caches latest value in mCommandBox.
   //Currently mCommandBox isn't available from
   //`TransferDataFromWindow` since parent window is destroyed.
   wxString mLastCommand;
 
   FileHistory mHistory;
};
 
class CLExportProcessor : public ExportProcessor
{
   struct
   {
      TranslatableString status;
      double t0;
      double t1;
      unsigned channels;
      wxString cmd;
      bool showOutput;
      std::unique_ptr<Mixer> mixer;
      wxString output;
      std::unique_ptr<ExportCLProcess> process;
   } context;
public:
 
   bool Initialize(AudacityProject& project,
      const Parameters& parameters,
      const wxFileNameWrapper& filename,
      double t0, double t1, bool selectedOnly,
      double rate, unsigned channels,
      MixerOptions::Downmix* mixerSpec,
      const Tags* tags) override;
 
   ExportResult Process(ExportProcessorDelegate& delegate) override;
 
private:
 
   static std::vector<char> GetMetaChunk(const Tags *metadata);
};
 
class ExportCL final
   : public ExportPlugin
{
public:
 
   ExportCL() = default;
 
   int GetFormatCount() const override;
   FormatInfo GetFormatInfo(int) const override;
 
   // Required
 
   std::unique_ptr<ExportOptionsEditor>
   CreateOptionsEditor(int, ExportOptionsEditor::Listener*) const override;
 
   std::unique_ptr<ExportProcessor> CreateProcessor(int format) const override;
 
};
 
int ExportCL::GetFormatCount() const
{
   return 1;
}
 
FormatInfo ExportCL::GetFormatInfo(int) const
{
   return {
      wxT("CL"), XO("(external program)"), {""}, 255, false
   };
}
 
std::unique_ptr<ExportOptionsEditor>
ExportCL::CreateOptionsEditor(int, ExportOptionsEditor::Listener*) const
{
   return std::make_unique<ExportOptionsCLEditor>();
}
 
std::unique_ptr<ExportProcessor> ExportCL::CreateProcessor(int format) const
{
   return std::make_unique<CLExportProcessor>();
}
 
bool CLExportProcessor::Initialize(AudacityProject& project,
   const Parameters& parameters,
   const wxFileNameWrapper& fName,
   double t0, double t1, bool selectionOnly,
   double sampleRate, unsigned channels,
   MixerOptions::Downmix* mixerSpec,
   const Tags* metadata)
{
   context.t0 = t0;
   context.t1 = t1;
   context.channels = channels;
 
   ExtendPath ep;
   long rc;
 
   const auto path = fName.GetFullPath();
 
   context.cmd = wxString::FromUTF8(ExportPluginHelpers::GetParameterValue<std::string>(parameters, CLOptionIDCommand));
   context.showOutput = ExportPluginHelpers::GetParameterValue(parameters, CLOptionIDShowOutput, false);
 
   // Bug 2178 - users who don't know what they are doing will
   // now get a file extension of .wav appended to their ffmpeg filename
   // and therefore ffmpeg will be able to choose a file type.
   if( context.cmd == wxT("ffmpeg -i - \"%f\"") && !fName.HasExt())
      context.cmd.Replace( "%f", "%f.wav" );
   context.cmd.Replace(wxT("%f"), path);
 
   // Kick off the command
   context.process = std::make_unique<ExportCLProcess>(&context.output);
   auto& process = *context.process;
 
   rc = wxExecute(context.cmd, wxEXEC_ASYNC, &process);
   if (!rc) {
      process.Detach();
      process.CloseOutput();
      throw ExportException(XO("Cannot export audio to %s")
         .Format( path )
         .Translation());
   }
 
   // Turn off logging to prevent broken pipe messages
   wxLogNull nolog;
 
   // establish parameters
   int rate = lrint(sampleRate);
   const size_t maxBlockLen = 44100 * 5;
   unsigned long totalSamples = lrint((t1 - t0) * rate);
   unsigned long sampleBytes = totalSamples * channels * SAMPLE_SIZE(floatSample);
 
   wxOutputStream *os = process.GetOutputStream();
 
   // RIFF header
   struct {
      char riffID[4];            // "RIFF"
      wxUint32 riffLen;          // basically the file len - 8
      char riffType[4];          // "WAVE"
   } riff;
 
   // format chunk */
   struct {
      char fmtID[4];             // "fmt " */
      wxUint32 formatChunkLen;   // (format chunk len - first two fields) 16 in our case
      wxUint16 formatTag;        // 1 for PCM
      wxUint16 channels;
      wxUint32 sampleRate;
      wxUint32 avgBytesPerSec;   // sampleRate * blockAlign
      wxUint16 blockAlign;       // bitsPerSample * channels (assume bps % 8 = 0)
      wxUint16 bitsPerSample;
   } fmt;
 
   // id3 chunk header
   struct {
      char id3ID[4];             // "id3 "
      wxUint32 id3Len;           // length of metadata in bytes
   } id3;
 
   // data chunk header
   struct {
      char dataID[4];            // "data"
      wxUint32 dataLen;          // length of all samples in bytes
   } data;
 
   riff.riffID[0] = 'R';
   riff.riffID[1] = 'I';
   riff.riffID[2] = 'F';
   riff.riffID[3] = 'F';
   riff.riffLen   = wxUINT32_SWAP_ON_BE(sizeof(riff) +
                                        sizeof(fmt) +
                                        sizeof(data) +
                                        sampleBytes -
                                        8);
   riff.riffType[0]  = 'W';
   riff.riffType[1]  = 'A';
   riff.riffType[2]  = 'V';
   riff.riffType[3]  = 'E';
 
   fmt.fmtID[0]        = 'f';
   fmt.fmtID[1]        = 'm';
   fmt.fmtID[2]        = 't';
   fmt.fmtID[3]        = ' ';
   fmt.formatChunkLen  = wxUINT32_SWAP_ON_BE(16);
   fmt.formatTag       = wxUINT16_SWAP_ON_BE(3);
   fmt.channels        = wxUINT16_SWAP_ON_BE(channels);
   fmt.sampleRate      = wxUINT32_SWAP_ON_BE(rate);
   fmt.bitsPerSample   = wxUINT16_SWAP_ON_BE(SAMPLE_SIZE(floatSample) * 8);
   fmt.blockAlign      = wxUINT16_SWAP_ON_BE(fmt.bitsPerSample * fmt.channels / 8);
   fmt.avgBytesPerSec  = wxUINT32_SWAP_ON_BE(fmt.sampleRate * fmt.blockAlign);
 
   // Retrieve tags if not given a set
   if (metadata == nullptr) {
      metadata = &Tags::Get(project);
   }
   const auto metachunk = GetMetaChunk(metadata);
 
   if (!metachunk.empty()) {
 
      id3.id3ID[0] = 'i';
      id3.id3ID[1] = 'd';
      id3.id3ID[2] = '3';
      id3.id3ID[3] = ' ';
      id3.id3Len   = wxUINT32_SWAP_ON_BE(metachunk.size());
      riff.riffLen += sizeof(id3) + metachunk.size();
   }
 
   data.dataID[0] = 'd';
   data.dataID[1] = 'a';
   data.dataID[2] = 't';
   data.dataID[3] = 'a';
   data.dataLen   = wxUINT32_SWAP_ON_BE(sampleBytes);
 
   // write the headers and metadata
   os->Write(&riff, sizeof(riff));
   os->Write(&fmt, sizeof(fmt));
   if (!metachunk.empty()) {
      os->Write(&id3, sizeof(id3));
      os->Write(metachunk.data(), metachunk.size());
   }
   os->Write(&data, sizeof(data));
 
   // Mix 'em up
   context.mixer = ExportPluginHelpers::CreateMixer(
      project, selectionOnly, t0, t1, channels, maxBlockLen, true, rate,
      floatSample, mixerSpec);
 
   context.status = selectionOnly
         ? XO("Exporting the selected audio using command-line encoder")
         : XO("Exporting the audio using command-line encoder");
 
   return true;
}
 
ExportResult CLExportProcessor::Process(ExportProcessorDelegate& delegate)
{
   delegate.SetStatusString(context.status);
   auto& process = *context.process;
   auto exportResult = ExportResult::Success;
   {
      size_t numBytes = 0;
      constSamplePtr mixed = nullptr;
 
      wxOutputStream *os = process.GetOutputStream();
      auto closeIt = finally ( [&] {
         // Should make the process die, before propagating any exception
         process.CloseOutput();
      } );
 
      // Start piping the mixed data to the command
      while (exportResult == ExportResult::Success && process.IsActive() && os->IsOk()) {
         // Capture any stdout and stderr from the command
         Drain(process.GetInputStream(), &context.output);
         Drain(process.GetErrorStream(), &context.output);
 
         // Need to mix another block
         if (numBytes == 0) {
            auto numSamples = context.mixer->Process();
            if (numSamples == 0)
               break;
 
            mixed = context.mixer->GetBuffer();
            numBytes = numSamples * context.channels;
 
            // Byte-swapping is necessary on big-endian machines, since
            // WAV files are little-endian
#if wxBYTE_ORDER == wxBIG_ENDIAN
            auto buffer = (const float *) mixed;
            for (int i = 0; i < numBytes; i++) {
               buffer[i] = wxUINT32_SWAP_ON_BE(buffer[i]);
            }
#endif
            numBytes *= SAMPLE_SIZE(floatSample);
         }
 
         // Don't write too much at once...pipes may not be able to handle it
         size_t bytes = wxMin(numBytes, 4096);
         numBytes -= bytes;
 
         while (bytes > 0) {
            os->Write(mixed, bytes);
            if (!os->IsOk()) {
               exportResult = ExportResult::Error;
               break;
            }
            bytes -= os->LastWrite();
            mixed += os->LastWrite();
         }
 
         if(exportResult == ExportResult::Success)
            exportResult = ExportPluginHelpers::UpdateProgress(
               delegate, *context.mixer, context.t0, context.t1);
      }
      // Done with the progress display
   }
 
   // Wait for process to terminate
   while (process.IsActive()) {
      using namespace std::chrono;
      std::this_thread::sleep_for(10ms);
      BasicUI::Yield();
   }
 
   // Display output on error or if the user wants to see it
   if (process.GetStatus() != 0 || context.showOutput) {
      // TODO use ShowInfoDialog() instead.
      BasicUI::CallAfter([cmd = context.cmd, output = std::move(context.output)]
      {
         wxDialogWrapper dlg(nullptr,
                   wxID_ANY,
                   XO("Command Output"),
                   wxDefaultPosition,
                   wxSize(600, 400),
                   wxDEFAULT_DIALOG_STYLE | wxRESIZE_BORDER);
         dlg.SetName();
 
         ShuttleGui S(&dlg, eIsCreating);
         S
            .Style( wxTE_MULTILINE | wxTE_READONLY | wxTE_RICH )
            .AddTextWindow(cmd + wxT("\n\n") + output);
         S.StartHorizontalLay(wxALIGN_CENTER, false);
         {
            S.Id(wxID_OK).AddButton(XXO("&OK"), wxALIGN_CENTER, true);
         }
         dlg.GetSizer()->AddSpacer(5);
         dlg.Layout();
         dlg.SetMinSize(dlg.GetSize());
         dlg.Center();
 
         dlg.ShowModal();
      });
 
      if (process.GetStatus() != 0)
         exportResult = ExportResult::Error;
   }
 
   return exportResult;
}
 
 
std::vector<char> CLExportProcessor::GetMetaChunk(const Tags *tags)
{
   std::vector<char> buffer;
 
#ifdef USE_LIBID3TAG
   struct id3_tag_deleter {
      void operator () (id3_tag *p) const { if (p) id3_tag_delete(p); }
   };
 
   std::unique_ptr<id3_tag, id3_tag_deleter> tp { id3_tag_new() };
 
   for (const auto &pair : tags->GetRange()) {
      const auto &n = pair.first;
      const auto &v = pair.second;
      const char *name = "TXXX";
 
      if (n.CmpNoCase(TAG_TITLE) == 0) {
         name = ID3_FRAME_TITLE;
      }
      else if (n.CmpNoCase(TAG_ARTIST) == 0) {
         name = ID3_FRAME_ARTIST;
      }
      else if (n.CmpNoCase(TAG_ALBUM) == 0) {
         name = ID3_FRAME_ALBUM;
      }
      else if (n.CmpNoCase(TAG_YEAR) == 0) {
         name = ID3_FRAME_YEAR;
      }
      else if (n.CmpNoCase(TAG_GENRE) == 0) {
         name = ID3_FRAME_GENRE;
      }
      else if (n.CmpNoCase(TAG_COMMENTS) == 0) {
         name = ID3_FRAME_COMMENT;
      }
      else if (n.CmpNoCase(TAG_TRACK) == 0) {
         name = ID3_FRAME_TRACK;
      }
      else if (n.CmpNoCase(wxT("composer")) == 0) {
         name = "TCOM";
      }
 
      struct id3_frame *frame = id3_frame_new(name);
 
      if (!n.IsAscii() || !v.IsAscii()) {
         id3_field_settextencoding(id3_frame_field(frame, 0), ID3_FIELD_TEXTENCODING_UTF_16);
      }
      else {
         id3_field_settextencoding(id3_frame_field(frame, 0), ID3_FIELD_TEXTENCODING_ISO_8859_1);
      }
 
      MallocString<id3_ucs4_t> ucs4{
         id3_utf8_ucs4duplicate((id3_utf8_t *) (const char *) v.mb_str(wxConvUTF8)) };
 
      if (strcmp(name, ID3_FRAME_COMMENT) == 0) {
         // A hack to get around iTunes not recognizing the comment.  The
         // language defaults to XXX and, since it's not a valid language,
         // iTunes just ignores the tag.  So, either set it to a valid language
         // (which one???) or just clear it.  Unfortunately, there's no supported
         // way of clearing the field, so do it directly.
         id3_field *f = id3_frame_field(frame, 1);
         memset(f->immediate.value, 0, sizeof(f->immediate.value));
         id3_field_setfullstring(id3_frame_field(frame, 3), ucs4.get());
      }
      else if (strcmp(name, "TXXX") == 0) {
         id3_field_setstring(id3_frame_field(frame, 2), ucs4.get());
 
         ucs4.reset(id3_utf8_ucs4duplicate((id3_utf8_t *) (const char *) n.mb_str(wxConvUTF8)));
 
         id3_field_setstring(id3_frame_field(frame, 1), ucs4.get());
      }
      else {
         auto addr = ucs4.get();
         id3_field_setstrings(id3_frame_field(frame, 1), 1, &addr);
      }
 
      id3_tag_attachframe(tp.get(), frame);
   }
 
   tp->options &= (~ID3_TAG_OPTION_COMPRESSION); // No compression
 
   // If this version of libid3tag supports it, use v2.3 ID3
   // tags instead of the newer, but less well supported, v2.4
   // that libid3tag uses by default.
#ifdef ID3_TAG_HAS_TAG_OPTION_ID3V2_3
   tp->options |= ID3_TAG_OPTION_ID3V2_3;
#endif
 
   id3_length_t len;
 
   len = id3_tag_render(tp.get(), 0);
   if ((len % 2) != 0) {
      len++;   // Length must be even.
   }
 
   if (len > 0) {
      buffer.resize(len);
      id3_tag_render(tp.get(), (id3_byte_t *) buffer.data());
   }
#endif
 
   return buffer;
}
 
static ExportPluginRegistry::RegisteredPlugin sRegisteredPlugin{ "CommandLine",
   []{ return std::make_unique< ExportCL >(); }
};