操作 Wave 文件(4): 获取 Wave 文件主块与子块的信息

有两个相关的结构体: TMMIOInfo、TMMCKInfo.

TMMIOInfo 是多媒体文件打开后的状态信息, mmioOpen 函数的第二个参数就是这个结构的指针.
现在先用到了 TMMCKInfo, 这是文件内部 "块" 的信息, 构成如下:

TMMCKInfo = record
  ckid: FOURCC;        {块标识}
  cksize: DWORD;       {块大小}
  fccType: FOURCC;     {格式类型标识}
  dwDataOffset: DWORD; {偏移地址}
  dwFlags: DWORD;      {附加信息}
end;

查找 "块" 需要通过 mmioDescend、mmioAscend 两个函数.

mmioAscend 是从子块跳出;

mmioDescend 是进入到子块; 进入子块是需要指定子块的 ckid 和父块信息;
mmioDescend 也用来查找主块(RIFF), 此时需要很少的信息就可以找到主块.

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测试代码:

---

unit Unit1;

interface

uses
  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
  Dialogs, StdCtrls;

type
  TForm1 = class(TForm)
    Button1: TButton;
    Button2: TButton;
    procedure Button1Click(Sender: TObject);
    procedure Button2Click(Sender: TObject);
  end;

var
  Form1: TForm1;

implementation

{$R *.dfm}

uses MMSystem;

const FilePath = 'C:\WINDOWS\Media\Windows XP 启动.wav';

//获取 RIFF 块的信息
procedure TForm1.Button1Click(Sender: TObject);
var
  hFile: HMMIO;
  ckiRIFF: TMMCKInfo;
begin
  //清空 ckiRIFF 结构体; 有些函数使用前要求必须清空, 即使不要求也还是清空的好.
  FillChar(ckiRIFF, SizeOf(TMMCKInfo), 0); {局部变量在清空前有垃圾数据}

  //打开文件, 获取句柄
  hFile := mmioOpen(PChar(FilePath), nil, MMIO_READ);

  //获取 RIFF 块的信息
  mmioDescend(hFile,        {文件句柄}
              @ckiRIFF,     {块信息结构的指针, 用于获取块的信息}
              nil,          {这父块的结构信息, RIFF 没有父块, 无需指定}
              MMIO_FINDRIFF {如果是查询子块这里的标志是 MMIO_FINDCHUNK}
             );             {返回 0 表示查找成功, 这里忽略了验证}

  //以下是查证获取到的信息
  ShowMessageFmt('%d, %d, %d, %d, %d', [ckiRIFF.ckid, ckiRIFF.cksize, ckiRIFF.fccType,
  ckiRIFF.dwDataOffset, ckiRIFF.dwFlags ]); {1179011410, 424636, 1163280727, 8, 0}

  if ckiRIFF.ckid = FOURCC_RIFF then ShowMessage('是 RIFF');
  if ckiRIFF.fccType = mmioStringToFOURCC('WAVE',0) then ShowMessage('是 WAVE');

  //关闭
  mmioClose(hFile, 0);
end;


//获取子块的信息
procedure TForm1.Button2Click(Sender: TObject);
var
  hFile: HMMIO;
  ckiRIFF,ckiSub: TMMCKInfo;
  n: Integer;
begin
  //清空准备接受信息的结构
  FillChar(ckiRIFF, SizeOf(TMMCKInfo), 0);
  FillChar(ckiSub, SizeOf(TMMCKInfo), 0);

  hFile := mmioOpen(PChar(FilePath), nil, MMIO_READ);

  //先获取主块(RIFF)信息
  mmioDescend(hFile, @ckiRIFF, nil, MMIO_FINDRIFF);

  //获取 fmt 子块信息
  ckiSub.ckid := mmioStringToFOURCC('fmt', 0);
  if mmioDescend(hFile, @ckiSub, @ckiRIFF, MMIO_FINDCHUNK) = MMSYSERR_NOERROR then
  begin
    ShowMessageFmt('%d, %d, %d, %d, %d', [ckiSub.ckid, ckiSub.cksize, ckiSub.fccType,
      ckiSub.dwDataOffset, ckiSub.dwFlags]);
  end;

  //如果继续查找需要跳出子块; 下面将从偏移地址 20 跳到 36 处
  mmioAscend(hFile, @ckiSub, 0); {其第三个参数一直是 0, 是备用参数}

  //获取 data 子块信息
  ckiSub.ckid := mmioStringToFOURCC('data', 0);
  if mmioDescend(hFile, @ckiSub, @ckiRIFF, MMIO_FINDCHUNK) = MMSYSERR_NOERROR then
  begin
    ShowMessageFmt('%d, %d, %d, %d, %d', [ckiSub.ckid, ckiSub.cksize, ckiSub.fccType,
      ckiSub.dwDataOffset, ckiSub.dwFlags]);
  end;

  mmioClose(hFile, 0);
end;

end.