Play Wave Backwards

uses ExtCtrls, MMSystem

const
  WM_FINISHED = WM_USER + $200;
  
public
    { Public declarations }
    fData: PChar;
    fWaveHdr: PWAVEHDR;
    fWaveOutHandle: HWAVEOUT;

    procedure ReversePlay(const szFileName: string);
    procedure WaveOutProc(hwo: HWAVEOUT; uMsg: UINT; dwParam1,
      dwParam2: DWORD);
    procedure WmFinished(var Msg: TMessage); message WM_FINISHED;
    
//

procedure Interchange(hpchPos1, hpchPos2: PChar; wLength: Word);
var
  wPlace: word;
  bTemp: char;
begin
  for wPlace := 0 to wLength - 1 do
  begin
    bTemp := hpchPos1[wPlace];
    hpchPos1[wPlace] := hpchPos2[wPlace];
    hpchPos2[wPlace] := bTemp
  end
end;

procedure waveOutPrc(hwo: HWAVEOUT; uMsg: UINT; dwInstance,
  dwParam1, dwParam2: DWORD); stdcall;
begin
  TForm1(dwInstance).WaveOutProc(hwo, uMsg, dwParam1, dwParam2)
end;

procedure TForm1.WaveOutProc(hwo: HWAVEOUT; uMsg: UINT; dwParam1,
  dwParam2: DWORD);
begin
  case uMsg of
    WOM_OPEN:;
    WOM_CLOSE:
      fWaveOutHandle := 0;
    WOM_DONE:
      PostMessage(Handle, WM_FINISHED, 0, 0);
  end
end;

procedure TForm1.ReversePlay(const szFileName: string);
var
  mmioHandle: HMMIO;
  mmckInfoParent: MMCKInfo;
  mmckInfoSubChunk: MMCKInfo;
  dwFmtSize, dwDataSize: DWORD;
  pFormat: PWAVEFORMATEX;
  wBlockSize: word;
  hpch1, hpch2: PChar;
begin
  { The mmioOpen function opens a file for unbuffered or buffered I/O }
  mmioHandle := mmioOpen(PChar(szFileName), nil, MMIO_READ or MMIO_ALLOCBUF);
  if mmioHandle = 0 then
    raise Exception.Create('Unable to open file ' + szFileName);

  try
    { mmioStringToFOURCC converts a null-terminated string to a four-character code }
    mmckInfoParent.fccType := mmioStringToFOURCC('WAVE', 0);
    { The mmioDescend function descends into a chunk of a RIFF file }
    if mmioDescend(mmioHandle, @mmckinfoParent, nil, MMIO_FINDRIFF) <>
      MMSYSERR_NOERROR then raise Exception.Create(szFileName + ' is not a valid wave file');

    mmckinfoSubchunk.ckid := mmioStringToFourCC('fmt ', 0);
    if mmioDescend(mmioHandle, @mmckinfoSubchunk, @mmckinfoParent,
      MMIO_FINDCHUNK) <> MMSYSERR_NOERROR then
      raise Exception.Create(szFileName + ' is not a valid wave file');

    dwFmtSize := mmckinfoSubchunk.cksize;
    GetMem(pFormat, dwFmtSize);

    try
      { The mmioRead function reads a specified number of bytes from a file }
      if DWORD(mmioRead(mmioHandle, PChar(pFormat), dwFmtSize)) <>
        dwFmtSize then
        raise Exception.Create('Error reading wave data');

      if pFormat^.wFormatTag <> WAVE_FORMAT_PCM then
        raise Exception.Create('Invalid wave file format');

      { he waveOutOpen function opens the given waveform-audio output device for playback }
      if waveOutOpen(@fWaveOutHandle, WAVE_MAPPER, pFormat, 0, 0,
        WAVE_FORMAT_QUERY) <> MMSYSERR_NOERROR then
        raise Exception.Create('Can''t play format');

      mmioAscend(mmioHandle, @mmckinfoSubchunk, 0);
      mmckinfoSubchunk.ckid := mmioStringToFourCC('data', 0);
      if mmioDescend(mmioHandle, @mmckinfoSubchunk, @mmckinfoParent,
        MMIO_FINDCHUNK) <> MMSYSERR_NOERROR then
        raise Exception.Create('No data chunk');

      dwDataSize := mmckinfoSubchunk.cksize;
      if dwDataSize = 0 then
        raise Exception.Create('Chunk has no data');

      if waveOutOpen(@fWaveOutHandle, WAVE_MAPPER, pFormat,
        DWORD(@WaveOutPrc), Integer(Self), CALLBACK_FUNCTION) <> MMSYSERR_NOERROR then
      begin
        fWaveOutHandle := 0;
        raise Exception.Create('Failed to open output device');
      end;

      wBlockSize := pFormat^.nBlockAlign;

      ReallocMem(pFormat, 0);
      ReallocMem(fData, dwDataSize);

      if DWORD(mmioRead(mmioHandle, fData, dwDataSize)) <> dwDataSize then
        raise Exception.Create('Unable to read data chunk');

      hpch1 := fData;
      hpch2 := fData + dwDataSize - 1;

      while hpch1 < hpch2 do
      begin
        Interchange(hpch1, hpch2, wBlockSize);
        Inc(hpch1, wBlockSize);
        Dec(hpch2, wBlockSize)
      end;

      GetMem(fWaveHdr, SizeOf(WAVEHDR));
      fWaveHdr^.lpData  := fData;
      fWaveHdr^.dwBufferLength := dwDataSize;
      fWaveHdr^.dwFlags := 0;
      fWaveHdr^.dwLoops := 0;
      fWaveHdr^.dwUser := 0;

      { The waveOutPrepareHeader function prepares a waveform-audio data block for playback. }
      if waveOutPrepareHeader(fWaveOutHandle, fWaveHdr,
        SizeOf(WAVEHDR)) <> MMSYSERR_NOERROR then
        raise Exception.Create('Unable to prepare header');

      { The waveOutWrite function sends a data block to the given waveform-audio output device.}
      if waveOutWrite(fWaveOutHandle, fWaveHdr, SizeOf(WAVEHDR)) <>
        MMSYSERR_NOERROR then
        raise Exception.Create('Failed to write to device');

    finally
      ReallocMem(pFormat, 0)
    end
  finally
    mmioClose(mmioHandle, 0)
  end
end;

procedure TForm1.WmFinished(var Msg: TMessage);
begin
  WaveOutUnprepareHeader(fWaveOutHandle, fWaveHdr, SizeOf(WAVEHDR));
  WaveOutClose(fWaveOutHandle);
  ReallocMem(fData, 0);
  ReallocMem(fWaveHdr, 0);
  Button1.Enabled := True;
end;

procedure TForm1.FormCloseQuery(Sender: TObject; var CanClose: Boolean);
begin
   WaveOutReset(fWaveOutHandle);
  while fWaveOutHandle <> 0 do
    Application.ProcessMessages
end;

procedure TForm1.Button1Click(Sender: TObject);
begin
  Button1.Enabled := False;
  try
    ReversePlay('C:\myWaveFile.wav')
  except
    Button1.Enabled := True;
    raise
  end
end;

procedure TForm1.Button2Click(Sender: TObject);
begin
  { The waveOutReset function stops playback on the given waveform-audio output device }
  WaveOutReset(fWaveOutHandle);
end;